High Oil Temps

As a lot of RV10 folks do, I have high oil temps. My Cyl temps never get above 380 even on very hot days in climb. My oil however keeps climbing up until I throttle back at about 220. Many attemps have been tried, by many folks to cool the engines better, most only partially successful.

I have the 2006 oilcooler in the standard Vans setup. I decided test wether the cooler was at capacity by increasing air flow over it with a cooling fan from an ATV. The fan really blows lots of air.

My tests to date indicate no additional cooling when I turn the fan on vs when I turn it off.

Just another data point in the search for excedllance.

Gary Specketer

Some oil Cooler mods RV-10

After 90 hours of flying and just now flying in 100 degree weather, I can say without a doubt that my cooling set up works very well.
While I do see Oil temps approaching 200F on really hot days and high climb out power, I make no adjustment for oil temps.
I did make a few changes to the standard oil cooling set up. The funnel you see is a 5 inch into 4 inch reducer and a smooth curve. I believe the additional louvers on the bottom of the cowl just below the oil cooler have a lot to do with the oil and Cylinder head temps. I also installed a curved baffle inside the cooler plenum.

Gary 40274 said:

As a lot of RV10 folks do, I have high oil temps. My Cyl temps never get above 380 even on very hot days in climb. My oil however keeps climbing up until I throttle back at about 220. Many attemps have been tried, by many folks to cool the engines better, most only partially successful.

I have the 2006 oilcooler in the standard Vans setup. I decided test wether the cooler was at capacity by increasing air flow over it with a cooling fan from an ATV. The fan really blows lots of air.

My tests to date indicate no additional cooling when I turn the fan on vs when I turn it off.

Just another data point in the search for excedllance.

Gary Specketer

Click to expand...

One cause of high oil temps (when everything with the baffling and cowling installation appears to be well installed) is excessive combustion gas blow-by because of poorly seated piston rings.
The hot blow-by gasses entering the oil sump, adding heat to the oil, that was intended to exit through the exhaust.
A cyl. compression check will not necessarily give an indication of this problem. Do you have any indications of blow-by, such as a lot of oil blow-by out the crankcase breather tube?

We have the exact opposite problem, trouble keeping the oil temp up in the cruise.

I notice you do not have your wheel pants and fairings on, I assume you are still running in the engine, and I say this because this is some common belief that the extra drag helps. It does not help anything. PUT THEM ON!!!

First flight maybe so you can check brakes etc, but after that put them on, if you want more drag......fly faster, and that will do it for you.

Tell us more about the hours flown the engines origins, and your break in procedure.

Also, is there any chance, even slight, even if you have checked before that the butterfly valve is closing in flight?

rvbuilder2002 said:

One cause of high oil temps (when everything with the baffling and cowling installation appears to be well installed) is excessive combustion gas blow-by because of poorly seated piston rings.
The hot blow-by gasses entering the oil sump, adding heat to the oil, that was intended to exit through the exhaust.
A cyl. compression check will not necessarily give an indication of this problem. Do you have any indications of blow-by, such as a lot of oil blow-by out the crankcase breather tube?

Click to expand...

Hmmm, outside of oil squirters, this is one of the best explanations I have heard regarding high oil temperature contributing factors. I have been chasing marginally high oil temps.

A few other data points. My oil temperatures are typically ambient temperature + 127 degrees. I have 63 hours on a TMX 0360 with electronic ignition and ECI cylinders. I use about a quart of oil every 6 hours.

I was able to drop oil temps 10 degrees by using a Stuart Warner 7 row oil cooler (dual pass) and another 3 degrees by plugging up various leaks in the baffle. Disconnecting the MAP line to the PMAG ignition so that the timing will emulate traditional mags will also make the engine run cooler. A 3 inch air dam on the bottom of the cowl allows me to climb at Vx with optimal CHT and oil temps. The dam has no impact on cruise temps.

OZ, the wheel pants were installed at about 15 hours and I can't remember that it made any difference. The oil cooler set up has been like this since new. I don't believe the butterfly valve ever moves unless I do so on purpose.
I know because I had it closed for run up on a cold day some time ago and the oil temperature reached 230F when I noticed on climb out.
I do believe rvbuilder2002 has a very valid point and it is possible that all of these mods may only be minor contributors to efficient oil cooling.
Based on my experience in building and flying an RV-8, I can say that the 8 used about twice as much oil and ran hotter than this engine. I also remember endlessly motoring around on the ground to double verify that all was well with the engine installation where this time I only ran the engine 2 or 3 times. Poorly seated rings are sometimes a result of glazing the cylinder walls after unnessesarily running the engine on the ground and without a cooling plennum installed.
Break in procedure was by the book with high power settings for the first 10 hours or so. 3 oil changes so far, average use 1qt per 12hours. No changes made since new.

More info

My engine has about 600 hours on it. I do not have problems from a cold start, only when it is hot outside and I come in to refuel and then head right out again, then I can get the 220 temps if I don't throttle back. Since I live in Minnesota in the summer, it is not usually a problem, but my quest is to make it better should we go to AZ or some other hot place in the summer.

I have been flying for 4 years with this so this is a marginal issue and only now have I had the time to investigate it further. My point was that I think we are at the max capacity of the cooler and if additional cooling is needed or wanted, a second cooler would be the solution, not better air flow.

Hope that clarifys things a bit.

Gary Specketer

I can't really tell but it appears there is an exit in your oil cooler air box? Maybe supplies air to the heat muff? This is not per plans at least not my plans, and looks like you may be losing a lot of cooling air out that side exit?

Sorry, not clear. Last reply was a question for Ernst.

2" flange?

The 2" flange on the inside of the plenum was for additional air if needed
and is capped off.
Unlike with my last airplane, I did not want to be bogged down with oil temperature problems and modifications in phase 1. It was just a provision in case it was needed.
It is definitely not needed.

Sorry Ernst, my comments were based on the original post, but looking at the photos thinking your photos were his......I will blame the iPad

My mistake!

rvbuilder2002 said:

One cause of high oil temps (when everything with the baffling and cowling installation appears to be well installed) is excessive combustion gas blow-by because of poorly seated piston rings.
The hot blow-by gasses entering the oil sump, adding heat to the oil, that was intended to exit through the exhaust.
A cyl. compression check will not necessarily give an indication of this problem. Do you have any indications of blow-by, such as a lot of oil blow-by out the crankcase breather tube?

Click to expand...

Very good point. I am sure I have this problem (standard channel-chrome cylinders) but it's not bad enough to replace the cylinders. I have seen this on several production airplanes, too. If this is the case, one should be careful about what permanent mods are made because correcting the blow-by problem may result in too much oil cooling.