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High Oil Temp Solutions?

Robb

Well Known Member
My new to me RV 7 has a 210 HP IO 360 and the oil temps seem high. It has a plenum on it with a Niagra Thermal oil cooler model 20002A mounted on the firewall with large scat tubing feeding it. The plenum cowling is sealed well and my CHT's are fine. It has been hot here lately in the high 80's to low 90's ambient. I saw 235 plus today running 23 squared at 8500 ft MSL with 80 degrees OAT. It was getting to 240 yesterday doing touch and go's and had to land as I was afraid to keep flying it. I have an Aviat Husky that never gets this hot and it looks like it has the same size cooler. It appears to have a scoop on the lower cowling that looks fairly restricted to be but I am not familiar with these planes. I was wondering if enlarging the opening a little will help? It does not look like there is much I can do and it may be that it will have oil issues in warm weather. I am sure it will be better when it cools off. It also looks like the way the plenum air goes over the engine it is already hot when it gets to the cooler. I have checked the sensor and it appears to be correct. Any ideas?
 
Get Some Assistance!

Hi Robb,
I'm another "new to me" kinda guy. I bought my RV-4 a few months back. It's my first ever airplane, the first taildragger I've ever flown, and the first experimental airplane I've ever flown. Since I bought my awesome airplane, I've learned an amazing amount about my airplane and the support community that's available here on VAF.

I respectfully recommend that you get some assistance with your airplane from your local EAA Chapter, other local RV owners, etc. In fact, I'm posting this in the forum (instead of PM'ing you) in hopes some of those folks will jump in and help.

The temps you're seeing aren't acceptable and they aren't normal. You've got a high performance engine in your -7 (good thing) but it doesn't appear the cooling design is working properly. You'll need to closely examine your baffling, cooler plumbing, and your engine operation technique to determine how to keep the temps in check. I suspect you have an airflow system design issue. Perhaps your oil cooler is mounted such that it simply doesn't get adequate airflow. I'm certainly no expert. I simply suggesting that you consult a few.

Best of luck,
Randy
 
Ran a second hose.

Hi Robb, I have a fiberglass plenum affixed to my large FW mounted oil cooler and as big as it is I could still use a little more cooling.

What I did was put another smaller 3" scat tubing in addition to the existing 4" to the fiberglass plenum (I made provisions for that when I built the plenum, just in case). Also I put a butterfly valve in the 4" tube so in cold weather I can cut off the larger hose. In the cold of the winter I was getting as low an oil temp as 140*. Now even in hot weather I rarely see 200* oil temp and in cold weather I am getting 155*+

Steve
 
Loose the plenum

Get rid of the plenum and use baffle seals instead. It will allow for a lot more airflow and air volume in the top area of the engine where it is especially needed for pattern work.

Vic
 
I have no experience with more than 180 HP in an RV but do know the larger engines create more heat. The challenge is getting rid of it. The oil cooler uses air already heated by the engine so when OAT is high, cht is up and oil temp is up more yet.

The last thing you are interested in is modifying an airplane you just bought and did not build. But you may have to in order to fly with OAT's in the 90's.

The cowl exit area is standard with the RV-7. It is the same with an angle valve engine as with a parallel valve engine. That area, about 56 inches square, restricts air flow through the engine compartment. It is a compromise attempting to achieve adequate cooling with minimum drag. Depending on the exhaust pipe system it is less than 56 inches, mine is about 49.2 with a 4 pipe system.

You can increase exit area easily by removing a section of the exit ramp going forward, lots of guys have done it, about 3 or 4 inches makes a difference and you can not see it except looking at the cowl from the bottom.

Another option is increasing oil cooler size and/or make. The old Stewart Warner coolers are the best and the cost a lot more too. Some guys have installed a larger cooler on the firewall and duct air to it through a 3 or 4 inch tube. I've done that although it really was not necessary with the 180HP parallel valve engine.

The bottom line with your engine is no mystery - the engine is producing more heat than the system can remove. More air flow across the cooler will help and so would a larger, better unit.

Welcome the the world of experimental aviation. :)
 
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Get rid of the plenum and use baffle seals instead. It will allow for a lot more airflow and air volume in the top area of the engine where it is especially needed for pattern work.

Vic
Quite a lot of assumptions here - If it is the stock Sam James, it is probably restricted, but not necessarily the problem - lets look at his cooler. It is the stock cooler for a parallel valve w/o piston cooling jets. By way of plenums, DanH's plenum configuration cools jut fine, but we all know it is well designed and implemented.

My new to me RV 7 has a 210 HP IO 360 and the oil temps seem high. It has a plenum on it with a Niagra Thermal oil cooler model 20002A mounted on the firewall with large scat tubing feeding it. The plenum cowling is sealed well and my CHT's are fine. It has been hot here lately in the high 80's to low 90's ambient. I saw 235 plus today running 23 squared at 8500 ft MSL with 80 degrees OAT. It was getting to 240 yesterday doing touch and go's and had to land as I was afraid to keep flying it. I have an Aviat Husky that never gets this hot and it looks like it has the same size cooler. It appears to have a scoop on the lower cowling that looks fairly restricted to be but I am not familiar with these planes. I was wondering if enlarging the opening a little will help? It does not look like there is much I can do and it may be that it will have oil issues in warm weather. I am sure it will be better when it cools off. It also looks like the way the plenum air goes over the engine it is already hot when it gets to the cooler. I have checked the sensor and it appears to be correct. Any ideas?

Some pictures of the cooler inlet would be helpful as would a general picture of the cooler installation. Do you have the Sam James plenum or something else? That cooler is the standard issue Vans cooler for non-cooling jetted parallel valve engines. It is likely part of the problem. Additional air might help, as you can get it up high off the baffle and reduce the reheated air issue, but I would first look at a larger capacity oil cooler. A bit of searching should reveal a good single pass cooler. DanH's work in his would be a good place to start. Much cooler oil will also help reduce CHT's a bit too, as the piston and barrel temps are linked to CHT.

My Lycoming manual says 435F is the CHT "limit" for 75% at cruise, and 245F oil temps at any time. Going to full throttle on TO with high oil temps would bother me the most due to rod bearing film thickness.

This is not to trash your comments , Vic, as you have a lot of experience and certainly chased more overtemp issues than I have, but hopefully would agree with my notes above.
 
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Other Threads

Hi Robb,

There are a good number of other threads that are worth reading. I know because I'm currently chasing a similar issue with my o-320. In my case, I believe I may have narrowed it down to loss of pressure differential between the upper and lower cowl chambers, caused by some cracks in the baffling material in the snout on the bottom. Haven't had a chance to test fly the fix yet, though. I've read of others who have found leaks on the cowl seam line, also. The lower cowl should be significantly lower pressure than the upper cowl to move the correct amount of air through the cylinders and oil cooler.

Here is a sampling of other threads you may find useful:

http://www.vansairforce.com/community/showthread.php?t=102094
http://www.vansairforce.com/community/showthread.php?t=17396
http://www.vansairforce.com/community/showthread.php?t=33416
http://www.vansairforce.com/community/showthread.php?t=20633
http://www.vansairforce.com/community/showthread.php?t=126414
http://www.vansairforce.com/community/showthread.php?t=123860
http://www.vansairforce.com/community/showthread.php?t=104139
http://www.vansairforce.com/community/showthread.php?t=52883
http://www.vansairforce.com/community/showthread.php?t=77317
http://www.vansairforce.com/community/showthread.php?t=73780
http://www.vansairforce.com/community/showthread.php?t=60168

There are more, too, if you play with your search terms. Good luck!

-jon
 
Thanks for all the help. I did speak with pacific oil coolers yesterday and they sent me some specs on a larger cooler. According to them the cooler is the standard vans cooler and is not adequate for the hp. I also have oil squirters on the bottom of the Pistons which add heat to the oil as well. The chts are low it's just the oil temp that concerns me. We have several great rv builders at kgoo and I will speak with them. One guy added an additional cooler that cured his problem.
 
Robb, you simply have a cooler that's too small. I'm up in Redding where it gets very hot. I've done two "high horsepower RV-7's. I used a 13 row cooler on both and neither has,a high oil temp issue. Every RV I build has a cooler larger than the one recommended by Van's. Even my own personal RV-8 has an oversized cooler. I've NEVER had high oil temps.
You can always block off part of the cooler during the winter months, but if your cooler is too small for your engine you have a problem.
 
Rob, your engine has oil squirters internally. This is why your oil is hot and your cylinders are OK. Your cooler is way to small. Use the cooler that is sold for the Rv10 with a 4 in. scat hose. It is a pain to install, but it is the only answer. Terry
 
The cooler model they sent me is an Aeroclassic 8001689. It looks like it will fit fine. I just need to make sure it is the correct one. It does remove a lot more heat than the one I have.
 
Should work well - and with an air supply valve it is adjustable for preventing oil cooler than 180F.

You might read the DanH's comparison of this two pass and the single pass (1001640) the same outside dimensions. It does have 6% less heat rejection, but the oil resistance is much lower.

http://www.vansairforce.com/community/showthread.php?t=44225

Either of these coolers should solve your oil temps. Keep us posted on your progress.
 
Thanks for all the help my new rv7 is a fantastic airplane and with my Husky I have the best of both worlds.
 
I have just the opposite problem. My oil cooler has the forward side completely covered and the oil barely gets warm enough o get into the normal range. Even on days 90 degree and up, it hardly gets to normal range. Defnately have an issue with the cooling of the oil.
 
Are you running Pmags? After lots of testing and documenting I am convinced Pmags increase your cylinder and oil temps.
 
My Dear RV pilots and builders
High Oil temp on RV7s is a recurrent subject. I don?t know why some engines run very hot on RV7s. My RV7A was built in 2011, South Carolina, has a 180HP inject Lycoming clone from mattituck and runs always hot. On summer with OAT about 26 C I early seen 115-118 C (end of yellow zone and even red)
I talk with mattituck and Vans, no solutions. I think the airplane is not correctly designed. My previous cessna with 210HP and 2750 RPM on take off never got hot even climbing with full throttle. Something is wrong on Vans RV7.
First I had the cooler mounted on FW, with a Vans wrong designed accessory called firewall mounted oil cooler. This accessory not spread the air over all cooler elements but only for the elements placed on cooler center.
I changed the cooler for Baffle?no improvement, still hot engine oil. The cylinder hide part of the cooler and is not a good space for cooler definitively.
Turned back the cooler to FW now with a 4`scat and a new designed like Funnel metallic accessory connecting scat to oil cooler. Slightly better better but far to solve the problem, still not OK. I fly on yellow (110-118 C) and 55 to 60% of power, no more
My aircraft spend the summers inside hangar because is intolerant to hot weather.
I asked Vans people about to install a 11 elements cooler instead the standard 7. They say no need, 7 is enough (((((. I can not fly in summer!!!!
Some people write about to open the outflow of cowling. Is the solution?
Why Vans not study a definitive solution? there are engineers there. They must solve so many issues with oil temp on RV7?

If a larger cooler is the solution what model and brand? fit on place? the scat can be conneted with baffle?

Any suggestion is welcome
Thanks:(:(:(
 
My Dear RV pilots and builders
High Oil temp on RV7s is a recurrent subject. I don?t know why some engines run very hot on RV7s. My RV7A was built in 2011, South Carolina, has a 180HP inject Lycoming clone from mattituck and runs always hot. On summer with OAT about 26 C I early seen 115-118 C (end of yellow zone and even red)
I talk with mattituck and Vans, no solutions. I think the airplane is not correctly designed. My previous cessna with 210HP and 2750 RPM on take off never got hot even climbing with full throttle. Something is wrong on Vans RV7.
First I had the cooler mounted on FW, with a Vans wrong designed accessory called firewall mounted oil cooler. This accessory not spread the air over all cooler elements but only for the elements placed on cooler center.
I changed the cooler for Baffle?no improvement, still hot engine oil. The cylinder hide part of the cooler and is not a good space for cooler definitively.
Turned back the cooler to FW now with a 4`scat and a new designed like Funnel metallic accessory connecting scat to oil cooler. Slightly better better but far to solve the problem, still not OK. I fly on yellow (110-118 C) and 55 to 60% of power, no more
My aircraft spend the summers inside hangar because is intolerant to hot weather.
I asked Vans people about to install a 11 elements cooler instead the standard 7. They say no need, 7 is enough (((((. I can not fly in summer!!!!
Some people write about to open the outflow of cowling. Is the solution?
Why Vans not study a definitive solution? there are engineers there. They must solve so many issues with oil temp on RV7?

If a larger cooler is the solution what model and brand? fit on place? the scat can be connected with baffle?

Any suggestion is welcome
Thanks:(:(:(
 
I think Daniels is correct. People from Vans not believe that 7 elements cooler is not enough for IO360 engines or with more power.
Daniels can we see photos of a large cooler mounted on FW? How you negotiate with engine mounting bars? easy to mount the Scat 4" or above?
Did you use the metallic funnel or built another ?Did you install the hat shape from vans?

Thanks

Antonio Costa
 
Costa,

I feel your pain brother!

I measured and checked all the items related to high oil and CHTs and still had the problem. In the end I went against all the advice I had gotten and installed a second oil cooler in series with the first one, (a SW8432R dual pass cooler).

The first cooler is on the firewall with Van's RV10 mount fed with 4" scat tube. The second one is a small Positech 6 row cooler plumbed in series with the first one.

The results are better than I hoped for, I actually close the 4" butterfly on the feed to the first cooler at times to keep the oil temps up above 180F. I may have to close off more in the winter or even put the second cooler on the shelf, but now I finally have adequate oil cooling and can run my engine at best power rich of peak settings when I want to and CHTs and Oil T stays within MY Limits.

One other point: Be aware that the factory recommended continuous running oil temperatures for Lycoming engines is 180F to 220F, and the factory recommended CHTs are much higher than we normally read about people running on these forums. Research the Lycoming manuals and make your own decisions.

Most people will tell you that you do not need and should not add a second cooler. I am just giving you one data point of an RV7A flyer that did so and likes the results. FYI, my engine is IO-375, low compression with oil squirters that add about 20F to normal oil temperatures. I run dual Pmags and have adjusted timing all over with no appreciable results. The second cooler worked for me.

Randall In Sedona
 
I posted a fix a few years back.
Same problem.
Opened the exhaust ramp by 2" and all was
Running cooler.

Hope it helps.
 
If anyone really wants to know what your real oil temps are monitor your sump oil temps. The oil temp probe that's usually mounted at the oil filter adaptor can very your temp reading from probe to probe. The oil is mixed, hot pump oil and cooled oil, right at the point where the probe is inserted. Long probes and short probes will likely give a different reading at this same point. (Shared data with Dan H.)

I monitor three points on my oil temps; The filter housing, the sump and the cooler output. I'm using a short Westach oil temp probe on the filter housing. My temps are typically at 85F OAT; 203F oil temp, 230F oil sump temp and 175F oil cooler out temp. SW 10599 cooler. A shorter probe will be more in the hot pump flow than the cooler oil flow.

This data is with an IO-360 180, 10:1, cold ind, dual Pmags, EIC set with no advance (25 degs). Adding advance to the Pmags dramatically increases oil temps another 15+ degs, adding more heat from higher CHT's. 20F to 40F degs increase on cruise settings. (A side note: When I used an ElectroAir I never got this heat increase).

There are more reasons for high oil temps than the cooler size or placement. You must consider what creates the heat that the oil is carrying away to the cooler. The cooler system must be efficient but if you're creating more heat than a typical cooling system can remove you will obviously have a net heat gain which will eventually top out at a given temp.

Before making assumptions that your oil temps are too high or too low you must know what you are actually monitoring. In the event your temps are actually too high then look for the cause of the heat, oil doesn't get hot all by itself, as well as the effectiveness of the cooling system.

In my case I can monitor my crappy Pmags with my EIC and monitor all my temps with an MGL iEFIS. I can easily follow the data and see the crappy Pmags are causing excessive engine heat which transfers to higher oil temp heat.
 
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I installed the larger oil cooler yesterday and while doing so I have a sheet metal shop so I had one of my guys fabricate a nice plenum on the inlet to the cooler and at the same time I routed the scat tube so there is minimal no ends in it. It did help a little but I did see 230 degrees on the electronic temp gauge. I am going to get an infrared meter and check it and see if the gauge us correct. I still have issues and I am thinking of opening the lower cowling a bit but that's a last resort as I doubt that's the issue. I have the Sam James plenum and oil squirters as well. I just don't see why my 7 runs hit when all my friends have 6's and they don't have issues. Starting to run out of options and getting ready to park it for a while and just fly my Husky until I figure it out. I know the plenum is efficient and maybe the inlet air is just too hot for the cooler to reject heat
 
I installed the larger oil cooler yesterday and while doing so I have a sheet metal shop so I had one of my guys fabricate a nice plenum on the inlet to the cooler and at the same time I routed the scat tube so there is minimal no ends in it. It did help a little but I did see 230 degrees on the electronic temp gauge. I am going to get an infrared meter and check it and see if the gauge us correct. I still have issues and I am thinking of opening the lower cowling a bit but that's a last resort as I doubt that's the issue. I have the Sam James plenum and oil squirters as well. I just don't see why my 7 runs hit when all my friends have 6's and they don't have issues. Starting to run out of options and getting ready to park it for a while and just fly my Husky until I figure it out. I know the plenum is efficient and maybe the inlet air is just too hot for the cooler to reject heat

You might get some thermocouples and measure air temps across the cooler, and the oil temp drop too, that will give you definitive information as to whether the air flow is low, inlet temps too high, or oil flow is low or temps too high or, the cooler is just still too small (just covering all the possible results of the data). All against a known ambient, and airspeed. A $100 meter from Omega (plus thermocouples) will have two channels and can measure this. DanH posted how to measure air pressures in upper and lower cowls too, that will help tell if there is an issue there. With the above, it should be easier to identify a more solid course of action for a solution.
 
To find out if your plenum and oil cooler is flowing air properly you'd need a manometer and get your differential readings. There's posted information on this subject. They show you how to make the piccolo tubes and placement. The meters are readily available online, fleebay of course, for not much $. You can read your pressures and see what you're pushing over the cylinders and thru the oil cooler. You just might be surprised.
 
Oil temps

Interesting find on temp prop length . I see Cirrus had a similar issue and issued a service bulitain.
 
Here's something interesting. I wanted a table of temperature vs ohms for a VDO oil temp sender...

http://www.aircraftspruce.com/catalog/inpages/vdosender323057.php?clickkey=134149

...which led me to a data sheet...

http://www.vdo-instruments.com/medi...5104620 Temperature Sensors_short_version.pdf

Spruce likes to assign its own part numbers, but cruise the VDO document and you'll find only one 150C sender with 1/8 NPT threads and a type C terminal, a #323-801-009-001D, about halfway down the third page of the document.

Here's the thing; see the "2" in the third column? That identifies the "Characteristic Curve Table", here found on page 11.

Read down the table to 85 C (aka a highly desirable 185F), then across to tolerance....which is plus or minus 10%.

Think about that. Two VDO senders can have outputs with as much as 20% variance between them. When stuck in the same hot oil, one could read 185F, and the next one may read 222F.

I admit to being amazed at how inaccurate this sender is, right from the box, brand new. Is this very sloppy tolerance an industry norm? If so, the very first thing to do about an oil temperature problem is check the sensor calibration....water pot and a candy thermometer, or similar.
 
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Here's something interesting. I wanted a table of temperature vs ohms for a VDO oil temp sender...

http://www.aircraftspruce.com/catalog/inpages/vdosender323057.php?clickkey=134149

...which led me to a data sheet...

http://www.vdo-instruments.com/medi...5104620 Temperature Sensors_short_version.pdf

Spruce likes to assign its own part numbers, but cruise the VDO document and you'll find only one 150C sender with 1/8 NPT threads and a type C terminal, a #323-801-009-001D, about halfway down the third page of the document.

Here's the thing; see the "2" in the third column? That identifies the "Characteristic Curve Table", here found on page 11.

Read down the table to 85 C (aka a highly desirable 185F), then across to tolerance....which is plus or minus 10%.

Think about that. Two VDO senders can have outputs with as much as 20% variance between them. When stuck in the same hot oil, one could read 185F, and the next one may read 222F.

I admit to being amazed at how inaccurate this sender is, right from the box, brand new. Is this very sloppy tolerance an industry norm? If so, the very first thing to do about an oil temperature problem is check the sensor calibration....water pot and a candy thermometer, or similar.

Dusting off the cobwebs, IIRC, the automotive industry uses some very sloppy tolerances for sensors, but requires that the offset and slope be known so electronic compensation can be applied. Otherwise a very cost effective sensor use is not possible. I don't remember how they determined the actual deviation, but I do remember that each sensor on an Isuzu Trooper on the engine had a 3D bar code calibration tag and as the engine was assembled, each part was scanned. At the end of the engine assembly line, an ECM was "built" with that calibration table for that specific engine. Nasty words came to bear when discussing what service parts had to be delivered, as (again IIRC) it was not possible for a dealer to change the calibration table, so a " nominal" component had to be "selected" for service use from production batches.

Having said all that, Dynon, and G3X guys should tell us how they manage to deliver an accurate number with such a wide variation in sensors. Anyone know who makes the oil temp RTD for Garmin? #494-70004-00?

This might just clue us in to why some RV's can not be cooled?!?!?!
 
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Cooler shroud

My "new to me" RV-6A has a firewall mounted cooler. The temperatures were always a little hot for me. I noticed during this year's condition inspection that the Van's supplied cooler shroud was longer in width than the oil cooler. A large amount of air was spilling out the sides. A little aluminum tape to close up the gaps resulted in the oil temperature dropping more than 20 degrees. I'm a happy camper!
 
Here's something interesting.

<big snip>

... the very first thing to do about an oil temperature problem is check the sensor calibration....water pot and a candy thermometer, or similar.

The question at that point is "Which one is correct?" The $8 candy thermometer or the $50 sensor? Same question for pressure sensors. Unfortunately, I don't have access to calibrated temperature or pressure gauges, so the calibration/verification process remains a challenge...
 
The question at that point is "Which one is correct?" The $8 candy thermometer or the $50 sensor? Same question for pressure sensors. Unfortunately, I don't have access to calibrated temperature or pressure gauges, so the calibration/verification process remains a challenge...

A $12.75 thermometer at +1F up to 158F should be better than +10%. Available from cole parmer
 
A $12.75 thermometer at +1F up to 158F should be better than +10%. Available from cole parmer

Heck, even Harbor Freight clams +/- 1.8 F for this $6 digital one

http://www.harborfreight.com/hand-tools/thermometers/instant-read-digital-thermometer-95384.html

And the same accuracy for this non-contact one -

http://www.harborfreight.com/hand-tools/thermometers/infrared-thermometer-93984.html

10% tolerance on temperature measurement is pretty lousy.
How many healthy folks would be diagnosed with a fever (or being almost dead) if household thermometers were that bad? Hypothermia starts at 104F, 10% error is 108F :)
 
Thank you! Got a pointer to a pressure gauge with good accuracy in the 60-90 PSI range?

picardfacepalm.jpg


Sorry, one per customer, you're gonna give engineers a bad name. Besides, you don't need oil pressure that accurate, it just needs to remain consistent with conditions.
 
Sorry, one per customer, you're gonna give engineers a bad name. Besides, you don't need oil pressure that accurate, it just needs to remain consistent with conditions.

I'm curious as to why my OP "dropped" 10+ psi when I switched from analog to digital gauges. Still in the green, but not as "green" as it was before.
 
I'm curious as to why my OP "dropped" 10+ psi when I switched from analog to digital gauges. Still in the green, but not as "green" as it was before.

Any oil pressure in excess of the "requirement" is only costing you engine power. Your loss of oil pressure probably gave you back .0002 GPH on your fuel burn. Feel better?
 
G3X guys should tell us how they manage to deliver an accurate number with such a wide variation in sensors. Anyone know who makes the oil temp RTD for Garmin? #494-70004-00?

Hello Bill,

Sorry I didn't see this sooner - we are also homebuilders and we read VAF all day the same as you, but sometimes we have to get some work done!

As is shown in the G3X installation manual, Garmin part number 494-70004-00 is a UMA 1B3-2.5R RTD sensor. The manufacturer of this sensor specifies a typical error of less than 2?C at 100?C.

As you can imagine, we prefer to use RTD or thermocouple sensors over thermistors whenever possible, because of their greater accuracy compared to the most commonly available automotive-style thermistors.

- Matt
 
I think I may have found the reason my oil temp is high. I started to look at increasing the scat tube size to 4 inch and when I removed the 3 inch tube from the rear Sam James plenum the tube is about 50 % restricted by the cylinder head and restricting the amount of free air the cooler receives. I am going to fabricate a square to round fitting out of aluminum and I bet that fixes it. No matter how large a cooler I install it won't help without air flow. I bet I am not the only one with this issue especially with high horsepower.
 
This may have been buried in the thread somewhere, but the standard procedure for calibrating temperature devices in the lab is as follows:

1) using clean water, distilled if possible, mix up a styrofoam glass full of ice water. As long as plenty of ice is present, the liquid water temp is exactly 0C (or 32F). Stir your temp probe around and note the reading. That is data point #1 (Note: pressure has a relatively insignificant effect on the freezing point for our purposes.)

2) heating the same clean water, distilled if possible, to boiling will give you exactly 100C (or 212F) at sea level. Correct for your altitude with the table below.

altitude correction table

Effect of pressure on freezing or boiling Note that the pressure axis isn't linear, i.e. anything near 1 atmosphere has little effect on the freezing point.

Using the 2 points you've just measured, you should be able to construct a useful calibration curve for your water or oil temp gauge! Easy, peasy!!
 
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