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High oil temps

vgb

Well Known Member
Hello rvers
I have a question. I have always fought high oil temps on my 7A, 0-360 carbed, with magnetos. Oil cooler behind the cylinder. Installed a steward warner oil cooler. Made sure the cowl was sealed, fiberglassed the tunnel on the top front cowl. New vernatherm
With the van,s supplied cooler in cruise it would climb to 240 degrees so would back off power to cool it down. New oil cooler helped a lot but still would like to run at least 200 degrees in cruise. Now with new cooler its about 215-220. If I do very much slow flight it will go to 240 degrees.pretty fast
Looking at the inlets and outlets with the exhaust pipes in the outlet it seems to me that I need to cut the opening up more.
Has anybody done this and does it help.
:( Vern
 
OAT & temps

That's pretty high for cruise temps. Needless to say, the other HUGE factor is OAT. You have to dissipate X BTU's which requires Y Temp change to get rid of the heat. Since oil temp is a direct heat exhanger, when the inlet air temp is high, the oil temp will be proportionally higher.

The high CHT's could also be directly caused by advanced timing... which causes more heat in the engine, which will raise oil temps also. I'd make sure your timing is correct, at least rule it out!!

Your top cowl inlet ramps are blocked off on at least one side so air can't escape behind them?
 
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I blocked off inlet ramps at one end and have checked timing several times.
Has anyone trimmed the outlet. I didn't really want to trim it but if it would solve the cooling it would be worth it.
Vern
 
Fuel Consumption?

What is your precise fuel consumption on take off and at what altitude is your
home field?
 
Vern, the questions asked are all good and important ones. I have a few more questions: - are you using the stock cowl and have you verified the oil temp probe's accuracy with boiling water? Also, fuel flow, MAP. and rpm at the cruise settings would be extremely helpful. CHT (and oil) temps are very sensitive to mixture on RV's.
 
Home field is 2725'. Take off is 14-gph at 8000' cruise 8.5 gph
Stock van's cowl with blocked air ramps.
I did not check probe with boiling water but landed and took cowl off and check with a heat gun at the probe. and it was within a couple of degrees.
2300 rpm at cruise.
vern
 
Vern,
I have the same setup as you and I flow about 15.5 gph after takeoff, but my field elevation is only 900' or so. I've been told this is a little low but my temps are good. Your carb may need to be modified to run richer. Check these threads: http://www.vansairforce.com/community/showthread.php?p=225706#post225706
http://www.vansairforce.com/community/showthread.php?t=86179&highlight=fuel+flow+takeoff
Post #29 in the first thread gives some figures about how much EGT rise should be attainable with a carb that is rich enough. If you do that test and have that much "room" for EGT rise your problem is elsewhere.
 
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Your Fuel flow seems to be in the neighborhood at that altitude where your engine is able to produce about 155 HP. (.55#of fuel/hp)
rv9av8tor pointed to ignition timing and ruling out too lean a mixture you are left with magneto timing. Your engine ID tag will tell you what the timing should be. 25 degrees BTDC for a low compression engine I am pretty sure.
It is highly unlikely that other factors contribute to such high oil and CH temperatures.
Since you posted that the plenum is well sealed and your oil cooler is obviously
working especially after you replaced it with a new one.
I am assuming that your probes are reading correctly.

Made sure the cowl was sealed, fiberglassed the tunnel on the top front cowl
Not sure what you mean by fiberglassed the tunnel?
 
Thanks for the help. I will ream the jet a little at a time. What number of ream can I expect to go to? I'm going to fly and watch the instruments closely.
I checked timing several times, so can't be that.
When someone solves a problem like this it would be good if they posted what solved the it.
I will post when I get this figured out.
Vern
 
Don't get too hasty boring out your carb jet.
Considering the fact that you are also running hot in cruise, where you are able to run full rich without affecting your temps, a lean mixture is not likely where you'll find the blame for your hot temps.
What is your compression ratio and where do you have your magneto set?
Do you have some pictures for us to look at, engine installation,upper and lower cooling and baffling installation, anything unusual?
If it's not fuel or ignition related it has to be something pretty unusual to generate temperatures like the ones you have.
 
Don't get too hasty boring out your carb jet.

Agree. Big picture:

Sometimes it "cures" the problem, but consider engine fundamentals. A very rich mixture is just an expensive way to reduce power. Rated power, the horsepower you paid good money to buy, is found at best power mixture, 100 to 150 ROP for an NA Lycoming. That mixture also results in the highest CHT and oil temp, hardly a surprise.

Assume reasonable OAT, correct ignition timing, and normal combustion (no detonation or preignition). Cylinder or oil temperature outside limits at full power indicates a cooling design problem, or a cooling installation problem, or both. A power reduction, however accomplished, is just a crutch.
 
All good information. I'm going to check everything all over again.
When I changed oil coolers it made a lot of difference. If I get cht down I think oil temps would drop to.

Vern
 
All good information. I'm going to check everything all over again.
When I changed oil coolers it made a lot of difference. If I get cht down I think oil temps would drop to.

Vern
 
Mr. Horton is absolutely correct about the carb mod. The only reason I even mentioned it was because the takeoff fuel flow seemed a little low. I had the richer profile kit put in my carb only after it was firmly established I was at or lean of peak at full rich and not even able to richen to "best power". As I remember my temps were not the biggest problem. Check all the other items mentioned in this thread first then only give the carb a look if you can't get that 100-150 degree rich-of-peak in flight.
 
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