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Oil Temperature Reduction

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dnickerson46

Member
This topic has been discussed many times. I have an Lycoming o-360 A1A in an RV-9A. The oil temperature runs a little hotter than I would like at 204 degrees, 9500 feet and 70% power, ROP. Is there a way to remove a section of the oil cooler inlet baffle to allow more airflow? If so, what would be the recommendation for how much to remove to lower the temp by 10 degrees?

I live in the Southeastern United States and the aircraft was built in the Northwest. I suspect the oil temps were fine in that part of the world.

I don't know if it makes a difference but I'm using 20W-50 weight oil which I'm going to replace with 100W at the next oil change.

The oil cooler has 7 cores and slanted so the left side is further out than the right side when looking at the engine.

Also, don't know if this is related but number cylinders #1 and #3 runs about 26 degrees hotter than the #2 and #4.
 
You should be fine running 20W-50, so that's probably not where the bang for the buck is. I'm not clear on what baffle is restricting air flow to the cooler. Assuming that the cooler is mounted on the baffle itself behind #4, are you saying that the finned surface area of the oil cooler is partially obstructed by baffling? Unless you're running in the wintertime and trying to get the oil temps a little higher, the entire surface area of the cooler should be unobstructed.

And of course, the standard questions just to clear the air... Are all of the flexible baffle seals facing the right way and showing proper wear on the top of the cowling? Are all of the inter-cylinder baffles sealed up all the way so that all the air is being directed properly (i.e. no leaks or bypassing)? Are the hoses to the oil cooler properly sized?
 
I've always wondered about this. According to Lycoming, they don't want more than 210F.
In the automotive world generally you want at least 100C (212F) so that you vaporize any water / moisture in the oil.

Thoughts... aka Hypothesis
a) Lycoming came up with this when oils weren't as good, and would breakdown at 220F or so. Oils have gotten better (at least auto oils) and they never updated their recommendations. Possibly because a raft of certified a/c engines would suddenly have the 'wrong' limits on the oil temp gauge.
b) Lycoming measures the oil temp in some relatively cold spot. Could be, I don't know.
c) Autos are running the oil hotter to reduce viscosity and boost mpg. Could be. Also synthetics appear to have higher temp tolerance than conventional oils.

So, should 205 even be concerning?
Would 195 be concerning as it would be too cool to evaporate moisture?

Regarding the "obstruction" question, I've seen people mount the oil cooler too low on the back of #4, so that the cylinder itself is partly blocking the oil cooler. Pic worth 1000 guesses.
 
I test flew in SoCAL during the hottest part of the year (September 1997). With the oil cooler mounted on the firewall, I ran redline oil temp most of the time. The bottom of the cowl exit was vertical with the firewall. I measured 2" forward from the aft end and cut off sloping up to the firewall creating a slightly larger exit area. This helped but still was not enough. Oil cooler relocated to behind #4 cylinder like most RV aircraft and saw a reduction in oil temp. Summary: 3" SCAT ducting is not large enough for good airflow to cool oil. Changing to a 3" X 5" opening in the baffle with oil cooler mounted on the engine mount fixed my issue. (Left side more forward than right side of cooler)

I typically run cylinder #1 and #2 hottest during full power climb and cylinder #3 and #4 hottest after stabling in cruise. On the LEFT coast, I would typically cruse with highest CHT at 390F. In the east, I am more like hottest now 375F.

Make sure that you calibrate your oil temp sensor. I boiled mine in water to make sure that the engine instrument read 212F. Spark advance also has had a large effect on operating temperatures on my airplane.
 
dnickerson46 said:
This topic has been discussed many times. I have an Lycoming o-360 A1A in an RV-9A. The oil temperature runs a little hotter than I would like at 204 degrees, 9500 feet and 70% power, ROP. Is there a way to remove a section of the oil cooler inlet baffle to allow more airflow? If so, what would be the recommendation for how much to remove to lower the temp by 10 degrees?

I live in the Southeastern United States and the aircraft was built in the Northwest. I suspect the oil temps were fine in that part of the world.

I don't know if it makes a difference but I'm using 20W-50 weight oil which I'm going to replace with 100W at the next oil change.

The oil cooler has 7 cores and slanted so the left side is further out than the right side when looking at the engine.

Also, don't know if this is related but number cylinders #1 and #3 runs about 26 degrees hotter than the #2 and #4.
Click to expand...
Aeroshell oil W100 is recommended to be used when surrounding air temperature is 60 to 89 F.

Good luck
 
Cooler cylinders mean less heat for oil cooler to disperse.

Consider removing some of the air dam in front of #1 and putting a washer spacer behind #3 (look for thread on baffle mods) which should help those cylinders.
 
blaplante said:
\Would 195 be concerning as it would be too cool to evaporate moisture?
Click to expand...

This point is frequently repeated but I think it is misunderstood. There are a several considerations:

1. Consider that the boiling point of water drops as pressure decreases - in other words, it drops as altitude increases.
2. More practically speaking, water doesn't need to boil to evaporate. Put some water in a pan on a stove at 150º F and see how long the water remains - it won't take long to evaporate even though it never reached a boiling point.
3. Consider that the point where most of us have the oil temperature probe is not at the point of highest oil temperature within the engine. It's essentially measuring the temperature of the oil entering the lubrication path, and it only gets hotter once it does. I've read that it warms up anywhere from 20 to 40 degrees depending on operating conditions etc.; others may have better data.

All in all, oil at 195º wouldn't make be concerned about it being too cold - I'd start wondering why it wasn't the usual 180º or less in cruise it usually is.
 
dnickerson46 said:
This topic has been discussed many times. I have an Lycoming o-360 A1A in an RV-9A. The oil temperature runs a little hotter than I would like at 204 degrees, 9500 feet and 70% power, ROP. Is there a way to remove a section of the oil cooler inlet baffle to allow more airflow? If so, what would be the recommendation for how much to remove to lower the temp by 10 degrees?

I live in the Southeastern United States and the aircraft was built in the Northwest. I suspect the oil temps were fine in that part of the world.

I don't know if it makes a difference but I'm using 20W-50 weight oil which I'm going to replace with 100W at the next oil change.

The oil cooler has 7 cores and slanted so the left side is further out than the right side when looking at the engine.

Also, don't know if this is related but number cylinders #1 and #3 runs about 26 degrees hotter than the #2 and #4.
Click to expand...
A few thoughts.

26* hotter on 1 and 3 isn’t bad at all. Not sure that is really worth chasing, IMHO.

I believe 20-50 is pretty much the same as 100w once it is to temp. Both are 50 weight at that point. The 20-50 will lower your oil pressure at start/cold engine.

Easy test, check your temp sender in oil you warm in the microwave. Put a kitchen thermometer in there and confirm at 180 or so.

What are you CHTs at 70% 9k’?
 
dnickerson46 said:
This topic has been discussed many times. I have an Lycoming o-360 A1A in an RV-9A. The oil temperature runs a little hotter than I would like at 204 degrees, 9500 feet and 70% power, ROP. Is there a way to remove a section of the oil cooler inlet baffle to allow more airflow? If so, what would be the recommendation for how much to remove to lower the temp by 10 degrees?

I live in the Southeastern United States and the aircraft was built in the Northwest. I suspect the oil temps were fine in that part of the world.

I don't know if it makes a difference but I'm using 20W-50 weight oil which I'm going to replace with 100W at the next oil change.

The oil cooler has 7 cores and slanted so the left side is further out than the right side when looking at the engine.

Also, don't know if this is related but number cylinders #1 and #3 runs about 26 degrees hotter than the #2 and #4.
Click to expand...
Have you checked the Vernatherm?
 
Cth6 said:
A few thoughts.

26* hotter on 1 and 3 isn’t bad at all. Not sure that is really worth chasing, IMHO.

I believe 20-50 is pretty much the same as 100w once it is to temp. Both are 50 weight at that point. The 20-50 will lower your oil pressure at start/cold engine.

Easy test, check your temp sender in oil you warm in the microwave. Put a kitchen thermometer in there and confirm at 180 or so.

What are you CHTs at 70% 9k’?
Click to expand...
Here is a snapshot from my EDM captured at 1 second intervals. At this point, CHT 1 is running a little high but it always does in this engine installation.

1718200035530.png
 
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RV6_flyer said:
I test flew in SoCAL during the hottest part of the year (September 1997). With the oil cooler mounted on the firewall, I ran redline oil temp most of the time. The bottom of the cowl exit was vertical with the firewall. I measured 2" forward from the aft end and cut off sloping up to the firewall creating a slightly larger exit area. This helped but still was not enough. Oil cooler relocated to behind #4 cylinder like most RV aircraft and saw a reduction in oil temp. Summary: 3" SCAT ducting is not large enough for good airflow to cool oil. Changing to a 3" X 5" opening in the baffle with oil cooler mounted on the engine mount fixed my issue. (Left side more forward than right side of cooler)

I typically run cylinder #1 and #2 hottest during full power climb and cylinder #3 and #4 hottest after stabling in cruise. On the LEFT coast, I would typically cruse with highest CHT at 390F. In the east, I am more like hottest now 375F.

Make sure that you calibrate your oil temp sensor. I boiled mine in water to make sure that the engine instrument read 212F. Spark advance also has had a large effect on operating temperatures on my airplane.
Click to expand...
I have also heard that spark advance can have an impact on operating temperatures. I have a SureFly mag on the right side and it is connected to cylinder #3 to sense MP. The folks at SureFly told me that the auto advance starts at a MP of 24 inches and the lower the MP goes, the more advance is added. To my knowledge, this is not adjustable. The auto advance can be shutoff but not adjusted.
 
dnickerson46 said:
I have not checked the Vernatherm but thanks for asking the question. To be honest, I didn't know what a Vernatherm was, did a search and came up with this useful article in Avweb https://www.avweb.com/ownership/oil-temperature-control-systems/
Click to expand...
I asked because a couple years ago my temps were running about the same or worse than your‘s. I pulled the Vernatherm and tested it in hot water, it didn’t move. I replaced it with a new unit, which I tested first, and temps came back to 180-190.
Good luck!
 
Skid said:
Have you checked the Vernatherm?
Click to expand...
My engine has a viscosity valve on the accessory case and should not have a Vernatherm but I'll check. Sometimes when a oil filter is added to an engine with a Vernatherm, the viscosity valve is not removed as it should be.
 
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