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Winter CHT and Oil Temperatures

SX-ALY

SX-ALY

Active Member
Hi

I'm posting that for a guy that i met at work place and owns (bought) an RV-7A. He is not member of any forums (i guess not an internet guy) and not a builder.
We talk a little about RVs and I told him that i 'm searching a lot in forums and builders sites and he ask me to post few questions here about his problem.
He experienced cold CHT (~250) and Oil temperatures (~165)now in that cold weather and he was thinking to reduce the cowl air inlets by placing an aluminum plate with smaller hole on it, so to reduce air coming into the cowl thus less cooling.

I didn't like the idea screwing aluminum plates in front of the cowl but he said he already tried that and he reduced the inlet size (by trying and error) by 50%!!
Results were good. He raises CHT to about 350 and oil to about 185+ in cruise which is pretty good for what i red here.
The problem he faces was that he lost Cabin Heat !! Obviously he got the cabin heat air input in the cowl air inlet so by reducing air flow there he reduces-eliminates cabin heat.
So to summarize the questions:

1. Are CHT temps at 200 -250F normal or too cold? Few posts i found the say over 200 is OK.

2. Blocking oil cooler only by Aluminum tape , shutter, etc or there is an oil temperature thermostat that he can use to raise the oil temps like that http://www.perma-cool.com/Catalog/Cat_page14.html
Anybody had success use that or something similar?

3. I found few post that builders block the cowl outlet like in this thread
http://www.vansairforce.com/community/showthread.php?t=12382&highlight=winter+inlet
What the advantage/disadvantage to do that at cowl inlet (i 'm guessing increase drag as one, besides reducing cabin heat in his configuration)
Also many uses Duct tape to reduces cowl inlet. How you apply it? How many layers, is it safe? Any pics, description?
Any other ways of doing that?

Thanks in advance

If there is any questions like type of oil cooler, etc i will pass them to him so i can have the answer.
I haven't seen the plane by myself.
 
You have had no answers so I will share my experience, but I am no expert.

I have an O-320 in a -4. You can get a bit more info if you go to my blog and look at the section on flight testing, including some engine parameter graphs.

1. 200-250 is lower than most. Is it a problem? I dont know. I am cruising well leaned, with a spread of temps plus/minus 20F around 300. Thats also cool. #1 and #2 are hotter in the cruise than #3 and #4. That reverses in the climb, though the spread tightens right up.

2. I have about a .5 sq inch hole left in the rear baffle wall (the rest is blanked off) at the entry to the scat that leads to the cooler. That puts the oil temp in the cruise in the 150/160 range. It only goes hotter climbing, or most of all at quite low power low speed in the circuit. Then it can just about get to 180. (With a high angle of attack I suspect the pressure rises around the cowl exit and the air flow reduces.) I am in the UK so a cold day is 32F.

3. If I had needed to reduce the air flow further I would have resorted to gaffer tape over the entries. I dont like the idea of further pressurising the engine cowls. I feel they are better suited to compression than inflation! However, having seen 180F, if briefly, I have decided to live like this for a while.

Hope that helps and stimulates more responses.

PS RV4 are known for over cooling.
 
oil cooler

if the 7 has 4" scat tube for cooling the cooler, there is slick 'valve' that you can use and it works great for the oil, which should also help the CHT. lbb
 
Steve Sampson said:
You have had no answers so I will share my experience, but I am no expert.

I have an O-320 in a -4. You can get a bit more info if you go to my blog and look at the section on flight testing, including some engine parameter graphs.

1. 200-250 is lower than most. Is it a problem? I dont know. I am cruising well leaned, with a spread of temps plus/minus 20F around 300. Thats also cool. #1 and #2 are hotter in the cruise than #3 and #4. That reverses in the climb, though the spread tightens right up.

2. I have about a .5 sq inch hole left in the rear baffle wall (the rest is blanked off) at the entry to the scat that leads to the cooler. That puts the oil temp in the cruise in the 150/160 range. It only goes hotter climbing, or most of all at quite low power low speed in the circuit. Then it can just about get to 180. (With a high angle of attack I suspect the pressure rises around the cowl exit and the air flow reduces.) I am in the UK so a cold day is 32F.

3. If I had needed to reduce the air flow further I would have resorted to gaffer tape over the entries. I dont like the idea of further pressurising the engine cowls. I feel they are better suited to compression than inflation! However, having seen 180F, if briefly, I have decided to live like this for a while.

Hope that helps and stimulates more responses.

PS RV4 are known for over cooling.
Click to expand...

Thanks Steve for your response. Seems like oil temperature is more important than CHTs. I red that you need to have 185 F at least once in any flight in order to eliminate any water condensation in engine. Gaffer (Duct tape) over the entries is something i red here in other posts, but i think aluminum plates to reduce inlets opening seems more safe idea. Comments?

lbgjb said:
if the 7 has 4" scat tube for cooling the cooler, there is slick 'valve' that you can use and it works great for the oil, which should also help the CHT. lbb
Click to expand...

Thanks Larry, can you provide a link of that product?
 
Oil cooler partially blocked

SX-ALY I am not flying yet but a friend of my has a 9 in Russia and he is blocking partially his oil cooler from the back. Very easy application. Flying in cold weather without any problem.My insert pic function has a glitch please provide me with your email address I will mail picture for your friend.
 
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Vladyspassky said:
SX-ALY I am not flying yet but a friend of my has a 9 in Russia and he is blocking partially his oil cooler from the back. Very easy application. Flying in cold weather without any problem.My insert pic function has a glitch please provide me with your email address I will mail picture for your friend.
Click to expand...

Thanks Vlad
thanosroger (at) yahoo (dot) com
 
I am trying a plate at the back

As the temps are dropping here in Ottawa, Canada I am trying something new. I installed a plate at the back of the baffle mounted oil cooler. There are unused holes there and it was easy to fab a rectangular plate and just bolt it to the cooler. I installed it yesterday but have not tried it yet. In warm weather my plane had consistent 180 degree oil but on my last cold flight I could only get 160 in a long climb. I will report back after my next flight. If it turns out not to be enough I will try a full coverage plate.
 
Jim Percy said:
Do you have a reference for these numbers? 210F sounds unnecessarily high to me.
Click to expand...

Lyco op manual, oil temp 180-245F
oiltemps.jpg
 
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The idea of running the oil at high temperatures is to "boil' off the moisture that condenses in the oil. The higher you can run oil temp, the better. (Up to a point)
I personally like to see my oil temps around 200-210F.
 
The chart look like...

Kahuna said:
Lyco op manual, oil temp 180-245F
oiltemps.jpg
Click to expand...

If it is cold outside the you can run at down to 160 degrees. Is this really OK?

I thought that you needed at least 180 degrees and when it is cold I start blocking off my oil air inlet.

Kent
 
plate works

I went out today with my new oil cooler plate installed. It was less than 5 degrees f outside and I was able to get 185 degree f oil temps when I leaned the engine during cruise at 25 squared.
 
Jim Percy said:
Do you have a reference for these numbers? 210F sounds unnecessarily high to me.
Click to expand...

Shell and Phillips lubrication engineers. 240F is pushing the max for oil temps. Running between 180 & 210F is no problem at all.

For every gallon of gas burned the engine produces over a gallon of water, most goes out the exhaust, some stays in the crankcase and is absorbed in the oil. Getting the oil hot (180-210F) every flight is a good thing to "flash off" the water out of the oil.

Another good tip is to remove the dip stick for 10-15 mins while you put the plane away. The amount of moisture (steam) coming out will amaze you! Also, if you check your oil when the engine is cold and see water beaded up on the dip stick (underside of threaded part), you have all the indications you need that you need hotter oil and vent the crank case after each flight.
 
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Geico266 said:
Shell and Phillips lubrication engineers. 240F is pushing the max for oil temps. Running between 180 & 210F is no problem at all.

For every gallon of gas burned the engine produces over a gallon of water, most goes out the exhaust, some stays in the crankcase and is absorbed in the oil. Getting the oil hot (180-210F) every flight is a good thing to "flash off" the water out of the oil.

Another good tip is to remove the dip stick for 10-15 mins while you put the plane away. The amount of moisture (steam) coming out will amaze you! Also, if you check your oil when the engine is cold and see water beaded up on the dip stick (underside of threaded part), you have all the indications you need that you need hotter oil and vent the crank case after each flight.
Click to expand...

Very nice advice and info Larry!

So, in cold weather you have, at least, to worry about oil temperatures and blocking part or all of the oil cooler you maintain a nice 180-210F.
What about CHTs?
My friend (RV-7A) went a trip from Cincinnati to Florida last Monday and we talked on the phone yesterday. He actually block part of the oil cooler and has no restriction(s) on cowl inlets. Oil temps were up to 180+ during cruise, cabin heat was good, but thinking reroute the inlet and may put a second heat muffler, CHTs were at 250F and he told me he was aware of shock cooling the engine during decent.
He decide to restrict the cowl inlets someway during winter and to be cabin controllable. I'm not sure if something like that exist out there, an adjustable cowl inlet diffuser maybe??
Any ideas?

Thanks everyone for posting so far.
 
SX-ALY said:
Very nice advice and info Larry!

What about CHTs?
Click to expand...

If his oil temps are 180F and his CHT's are 250F I think he just needs to fly more! Sounds like a great set up to me. I don't think he has to be too worried about shock cooling. There is a lot of vudo out there and shock cooling is on the "Top 10 list". Just tell him to fly it like he stole it. ;) Obviously, within reason.

JMHO
 
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kentb said:
If it is cold outside the you can run at down to 160 degrees. Is this really OK?

I thought that you needed at least 180 degrees and when it is cold I start blocking off my oil air inlet.

Kent
Click to expand...

Kent, I have looked at that several times and wondered also. My assumption is the logic is like this.

If the air is below 10F it will be very dry, so water in the sump will evaporate very easily, and therefore the oil will dry out this way. At 160F the oil will do its lubrication just fine, so the spec is accepting the reality of the situation.
 
Cruising in the current UK cold weather, hard to get CHTs above 150C (300F) and often lower - say 130C (265F). A climb, or aerobatics / tailchasing might see them approaching 180C (355F) so from the above seems great. Not a lot higher in summer (not that we had one!).

Oil T was far too low... 50C-60C (120F -140F). Last winter we taped up the Oil Cooler to raise them. Now we are cowlings off only every ~50hrs we have fitted the Van's variable Oil cooler and try to get the Oil T up to ~80C+ (180F) once per flight / day. Proving hard right now even closed.

From the above posts, I'd rather be in the "too cold" area than too hot, and hopefully good for engine life. Interesting that the "ideal" Oil T does drop with OAT... and we can achieve those numbers.

Ellie is more experienced at little aeroplane flying, and says serious "water in oil" / condensation can be seen on the dipstick? Also whilst opening the dipstick after flight is a good idea... it does run the risk of :(

Andy & Ellie Hill
RV-8 G-HILZ
 
There was also the question of shock cooling mentioned/queried in this thread, which is a summer and winter issue. Discard it if you will, but I would suggest the experience of Lasham Gliding Club (to 18000 tows a year) might be worth reviewing before you do. I wrote this before, and provided a link to a related paper . The post is here.
 
Thanks Larry,Mike, Andy (or Ellie) and Steve for your posts. I 'll pass all info to my friend.


Steve this a nice article about shock cooling, thanks for sharing.
I also review your web site and i have a question for you. Sent PM


I also have another question about how you route your cabin heat system.
I see that many use the aft engine baffle and connect a scat as inlet to muff exhaust heater and few others have an inlet with scat in front of Cylinder #1.
Are any advantages/disadvantage to go either way? Depends on engine, space available, Exhaust in use etc?

Thanks
 
What about the Vernatherm?

It has always been my practice in Minnesota flying to leave the oil cooler alone because when it is cold the vernatherm does not allow any oil to flow through the cooler any how.

I have always closed off the inlets to bring the CHT's in line and let the oil take care of itself.

My old brain can't quite figure out what good a butterfly valve on the oil cooler SCAT line does if there is no or very little oil going through the cooler. Can someone enlighten me?

Gary Specketer
 
Don't forget the breather!

As for blocking off cooling air going into the cowl, most every aircraft that I have provided a factory cooling plate for the crew has been left unused. The crews prefer duct tape. (Cessnas) I use an aluminum plate with a 1/4" flange that the air "goes around" to cover about 1/3 of the cheek holes taped in place. Aluminum tape over 1/2 the oil cooler.
The crankcase breather has a small slit right after it leaves the engine. It's called a whistler, and its purpose is to keep crankcase pressures from building up and BLOWING OUT THE FRONT OIL SEAL when the steam from the breather condenses and freezes plugging the line as it exits the cowling. This line is also insulated. We typically launch down to 10 below, although 20 or 30 below is O.K. if we know that there is a temperature inversion.
 
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