What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

High CHT, low oil temps

S

SwimmingDragonfly96

Well Known Member
My new to me RV7a seems to have a cooling issue during climb. O-360-A1A With a CS prop both 280TTSN Hobbs. After takeoff, I rapidly hit 400+ and have to nose down to keep it right around 425 degrees, which is quite consistent across all cylinders and persists until backing off the MP. This is immediately after takeoff, on the first take off of the day, hot or cold out. Weirdly enough, I notice that if I go into the pattern for touch and goes, my temps will stay in the 390s even with a much steeper climb? It is immensely annoying doing a 500-800 fpm climb in my performance loaded airplane. Once I’m in cruise everything settles down to around 350-380 across all cylinders even at high performance cruise.

On a separate note, my oil temps are always quite cool, rarely over 170 and usually 150-160 lately in the cooler temps we’ve been seeing in California the past couple of months. I am more or less not burning any oil and the oil looks like a nice amber color on the dipstick even after 30 hours flying time.

Any ideas? Mag timing was checked about 10 hours ago but everything else is fair game.
 
Lots of possible causes.
More info could help diagnose.

Was your mixture cable/control checked to ensure proper Air/Fuel ratio?
Maybe you're running too lean A/F ratio even with the red knob full in?
What does your EGTs show (if installed) This can be subjective due to probe placement.
At what IAS are you typically climbing?

As for oil temps, what size cooler do you have?
I presume you have the proper oil weight/grade for the air temperatures?

You could try to partially block the airflow through the cooler?
 
Last edited:
Seems odd that you get pretty different CHTs for the same routine on the 1st flight vs others. That kind of points to something that is different on the 1st flight. Normally I would say something is moving as it warms up, but you said first flight with a heat soaked engine is the same problem as first flight with a cold engine. At a loss on explaining that.

First place to look is timing. Might be worth double checking as more advance=higher CHTs. What did you time them at? Too low of a fuel flow at 100% power is also a possibility. Worth spending time understanding your peak EGT and seeing how far ROP you are during those take off/initial climbs. 200-250 ROP @ 100% power is a good range. Some carbs tend to run a bit lean when WOT in an RV. Verify that the mixture arm on the carb is moving fully to the rich stop. Several builders do this wrong and should have been caught in a pre buy.

Last is baffling issues. The fact that you get up to 380 in cruise in cooler wx points to a problem with cooling air flow. That said, I have no experience with AV engines and suppose that could be normal. I barely see 350 in summer time cruise on the 540, but that is a PV. Winter cruise is closer to 310. Then again I cruise LOP and best power will produce more heat. You didn't post details about cruise. Lots of posts here to help tidy that up and increase cooling performance. IMHO, this is the most likely place to find a solution. Some builders go the extra mile to seal things up and others don't.

I see similar oil temps in the winter. Lots of opinions on this, but it falls in to Lycoming's acceptable range, so it doesn't bother me at all. Others go rushing for tape or shutters. Need to do some research and form your own opinion.

Larry
 
Last edited:
riseric said:
Lots of possible causes.
More info could help diagnose.

Was your mixture cable/control checked to ensure proper Air/Fuel ratio?
Maybe you're running too lean A/F ratio even with the red knob full in?
What does your EGTs show (if installed) This can be subjective due to probe placement.
At what IAS are you typically climbing?

As for oil temps, what size cooler do you have?
I presume you have the proper oil weight/grade for the air temperatures?

You could try to partially block the airflow through the cooler?
Click to expand...


Thanks for all these suggestions. I had a pre buy done by an A&P/DAR and RV builder so I'm hoping he looked at the mixture adjustment. I haven't closely monitored CHT on climbout, but 1300s rings a bell. I am having to get my speeds up to past 120 before I can get any real climbs in, sometimes it's still struggling in the 420s at 130-140, until I back off the RPM to 2500 with the prop control.

Not sure about my oil cooler, but it's in the green range usually so I'm not too worried. I just don't see many threads indicating these two issues concurrently, and was curious if they could be related. I'm using aeroshell 15w50 and that's what the plane has gotten since its birth.

It'll be going to team light aviation in the bay in a couple of weeks, I'm hoping the guys over there can figure it out.
 
lr172 said:
Seems odd that you get pretty different CHTs for the same routine on the 1st flight vs others. That kind of points to something that is different on the 1st flight. Normally I would say something is moving as it warms up, but you said first flight with a heat soaked engine is the same problem as first flight with a cold engine. At a loss on explaining that.

First place to look is timing. Might be worth double checking as more advance=higher CHTs. What did you time them at? Too low of a fuel flow at 100% power is also a possibility. Worth spending time understanding your peak EGT and seeing how far ROP you are during those take off/initial climbs. 200-250 ROP @ 100% power is a good range. Some carbs tend to run a bit lean when WOT in an RV. Verify that the mixture arm on the carb is moving fully to the rich stop. Several builders do this wrong and should have been caught in a pre buy.

Last is baffling issues. The fact that you get up to 380 in cruise in cooler wx points to a problem with cooling air flow. That said, I have no experience with AV engines and suppose that could be normal. I barely see 350 in summer time cruise on the 540, but that is a PV. Winter cruise is closer to 310. Then again I cruise LOP and best power will produce more heat. You didn't post details about cruise. Lots of posts here to help tidy that up and increase cooling performance. IMHO, this is the most likely place to find a solution. Some builders go the extra mile to seal things up and others don't.

I see similar oil temps in the winter. Lots of opinions on this, but it falls in to Lycoming's acceptable range, so it doesn't bother me at all. Others go rushing for tape or shutters. Need to do some research and form your own opinion.

Larry
Click to expand...


Hey Larry,

Thanks for your words. As far as everything I've researched, I've found that my cruise CHTs for my set up are quite normal and consistently in the 350-380 range. Never over 380 in cruise, but occasionally under 350.

For takeoff with a heat soaked engine, I believe you may have misunderstood. I do think that if my engine is warm, my CHTs are much better on climb out. I know compression doesn't necessarily correlate with the state of an engine, but my compressions are all 79-80/80 with the engine cold.

I'm not necessarily fretting the low oil temps, I was more curious if someone could connect the dot between these two things since it seems like an unusual combo of symptoms.
 
Twin ASA cowl flaps go a long way to keeping CHTs down. In winter I can get away with 80KIAS climb (20 degrees nose up) but at around 60 degrees OAT I go with 95KIAS. In summer, quick transition to 500fpm climb works from pattern to any altitude.
Ref oil temps, yours are typical of cool/cold weather. Many threads about blocking the oil cooler, but so far few report any effect.
 
Long taxi?

My -9A does that. I have to manage CHTs to keep them under 400F on the 1st takeoff of the day, but they're cooler on subsequent touch-and-goes. Oil temps are always acceptable.

I've attributed this mostly to the frequent 15-20 minutes it takes to taxi from the hangar, runup, and queue for traffic at our busy GA airport.
 
SwimmingDragonfly96 said:
For takeoff with a heat soaked engine, I believe you may have misunderstood. I do think that if my engine is warm, my CHTs are much better on climb out. I know compression doesn't necessarily correlate with the state of an engine, but my compressions are all 79-80/80 with the engine cold.
Click to expand...

Ok, so with a cold engine, the CHTs climb to a much higher level during TO/climb than if the engine was hot or heat soaked. That is counter to what most would expect and seems odd. I would be looking for something that is expanding due to heat or contracting due to cold that would explain the difference. Have a good deal of confidence that the lower oil temps are not related to this issue. Possibly something odd happening in the carb.
 
Those are not unusual numbers for a RV7A with a (I)360 engine. Of course, it will not hurt to check your baffles and makes sure they are nicely setup with as little holes as possible. Some other tricks are done for the lower portion of the baffle which does help with CHT.

Do you have electronic ignition? If so, advanced timing does contribute to a higher CHT.

My RV7A had similar numbers, I would hit 400 CHT after about 2000' of climb. Once lowered the nose and let the number come down (to upper 300) then I could continue my climb and it would rarely go back above 400. The oil temp was low to the point that I had installed a shutter for winter operation.

I do advise against modifying the cowl (i.e cowl flap or similar) for more exit air, until all typical remedy has been tried.
 
Amir,
I think what you are seeing is pretty common. I have an RV6 with an O-360-A1A, and see almost the same thing. Only difference is my fixed pitch prop. You might want to try pulling the RPM back to 2500-2550, leaving the throttle wide open - that helps if your carb has a power enrichment jet - mine does. When it was warmer out, I had to pull my throttle back a little on initial climb to keep my CHT’s below 400 because of the FP prop. My oil on the other hand struggles to reach 160-170 this warmer than normal winter in Ohio, and that is with the airflow to my firewall mounted 7 row cooler 100% blocked off. I’m just barely out of phase1 (50 hours), so I’m thinking my CHT’s will temper with more hours.

When I had a CS prop on previous RV’s, I just left the throttle wide open, both carbed or fuel injected most of the time on a cross country. At 8-10,000’ cruise power was set using the prop control. Throttle left full from takeoff to the second half of descent, turbulence permitting. Might help with your CHT control. Tight baffles come first though.
Too cool oil is the oil temperature problem that is much easier to deal with. Count your blessings.
 
Temps

Not an RV, very tightly cowled 0 320. Cooler oil temps absolutely will cause slightly but measurably higher CHT. This would probably be more noticeable with single grade oil.
The standard protocol for a Constant Speed would be a poser setting of 25"/2500 as soon as a comfortable altitude is reached. Try leveling off, setting 25 square and accelerate to at least 120 knots, 130 is better. Reaching that speed resume climb and note CHT. Repeat with full throttle 2500 r/m.
425 is not a problem as long as not for extended periods. Try not to exceed 425. 400 is a good target but really only necessary for break in.
 
SwimmingDragonfly96 said:
My new to me RV7a seems to have a cooling issue during climb. O-360-A1A With a CS prop both 280TTSN Hobbs. After takeoff, I rapidly hit 400+ and have to nose down to keep it right around 425 degrees, which is quite consistent across all cylinders and persists until backing off the MP. This is immediately after takeoff, on the first take off of the day, hot or cold out. Weirdly enough, I notice that if I go into the pattern for touch and goes, my temps will stay in the 390s even with a much steeper climb? It is immensely annoying doing a 500-800 fpm climb in my performance loaded airplane. Once I’m in cruise everything settles down to around 350-380 across all cylinders even at high performance cruise.

On a separate note, my oil temps are always quite cool, rarely over 170 and usually 150-160 lately in the cooler temps we’ve been seeing in California the past couple of months. I am more or less not burning any oil and the oil looks like a nice amber color on the dipstick even after 30 hours flying time.

Any ideas? Mag timing was checked about 10 hours ago but everything else is fair game.
Click to expand...

You didn't mention which carb you are running. If it is a 10-3878 without the Mooney mod they run lean at WOT which will help cause high CHT's. Look for slag in between the cooling fins around the head area (can make a big difference), make sure the inter cyl baffles are well sealed as well as the rest, try reducing timing a couple degrees and see what happens...

You may just need to add a shutter (AntiSplat has them) in front of your oil cooler to get the oil temps up. Mine is rarely wide open to run 185F and is fully closed all winter and still never gets close.
 
Before I went to fuel injection, my O-360 did the same thing. The carb needed the main jet reamed out, but I left it alone because it ran very well LOP. My solution was to back the timing advance off to 23*. I could not tell any reduction in power at all; but the CHT's came down +- 50*...

As to oil temperatures; my norm without shuttering is 130 to 140F. I found that closing off the cooler, with my anti-splat shutter, until I see 180 to 190F, My engine seems to use less oil.
 
Last edited:
If your EGT is 1300 with the red knob all the way in after takeoff I suspect you are a bit lean. You probably peak at 1400 to 1450 and that’s not going to give you the 200 to 250 desired range. You don’t want to be lean for takeoff when the summer temps show up.
 
Last edited:
I would suggest a first look at all the cylinder baffling metal and rubber seals in and around the cyl heads and cylinder base. Air flow ( ie leakage )would be my first attempt to evaluate and correct. As mentioned above engine timing also has significant effects on CHT. Recommend to double checked against the engine timing name plate. Also check and see which orfice main jet that engine has in the carb. It should be part of the numbers on the carb name plate. Not that it has the wrong one but , your RV application may require a different size orifice. Also just because the name plate says xx-xxxx doesn't necessarily mean that's what's installed! It sound like it may be a bit lean. I know of several 0360 s that have to open up the main jet ( very small amount) to get the proper CHT on RVs . There's a lot of threads on VAF with main jet orifice size that may provide some direction.

Best of luck
 
Thanks for all your replies. I know the mag timing was set to 25 BTDC, maybe I'll try advancing that a bit (to the suggested 23?) and see if that helps? I'll also, of course, give my baffling a good thrice over to make sure everything is sealed up properly. If I can't make any headway here, I'll go ahead and try the Mooney mod.

Hope I can climb away from the runway the way I'd like to after this!
 
Temperature balance

When I bought my RV-8 it would get high cht in climb and the oil never got above 150F. I partially covered the front of the oil cooler with foil tape and that solved both issues. Too much air was going through the cooler and not enough through the cylinder fins. I adjust the amount of tape for summer and winter to keep oil temps up around 170-180F.
 
I had a similar problem. I run two PMags and had to add the jumper to them to make the spark advance a little less aggressive. Once I did that the cylinders cooled down quite well.
 
Spinner etc.

Does your spinner have the "fill plates" installed between the backplate and the aft side of the blades. I see these left out frequently. It disturbs the airflow there which reduces the flow into the cowl.

I second the comments to really study the baffling, especially look at the front interfaces to the cowl. Lots of stuff gets missed there. Also check the fit of the lower inter-cylinder baffles to the case. Shine a light up from the bottom. See any light? FIX IT.
 
blaplante said:
Does your spinner have the "fill plates" installed between the backplate and the aft side of the blades. I see these left out frequently. It disturbs the airflow there which reduces the flow into the cowl.

I second the comments to really study the baffling, especially look at the front interfaces to the cowl. Lots of stuff gets missed there. Also check the fit of the lower inter-cylinder baffles to the case. Shine a light up from the bottom. See any light? FIX IT.
Click to expand...

I will check out the spinner this weekend while I'm at the plane. Thanks for the suggestions!
 
Looking through my lycoming paperwork, it appears I have the 10-4164-1 carburetor. I believe this carb has a larger jet size so seems like lean mixture might not be my issue?
 
Last edited:
You must log in or register to reply here.
Back
Top