High oil temp

[thompsonbr87]

Recently purchased RV-6A, and my first task is getting oil temperatures under control. Cruising probably 85 deg at 3500, the engine needed to be managed diligently to avoid redlining oil temp. I'll be sure to get more exact conditions and power settings next time out. Engine is an IO-320-C1A with piston squirters (which I understand contributes to the high oil temp), but I've found advice that indicates the standard oil cooler should still be sufficient. Oil cooler is mounted on the firewall. Ducting to the oil cooler strikes me as a possible trouble spot with that big bend in the scat tube. I also have read that openly venting the oil cooler into the lower cowl reduces the pressure differential between the air inlet and outlet. Am I on the right track here? Any suggestions of things to do or check? Or should I just spring for the bigger cooler?

[erich weaver]

What size is the scat hose going to the cooler?

Erich

[BillL]

Barrett, many things can contribute to high oil temperatures. One question is has it always been this way.

Basics, either the heat rejection to the oil is too high or the cooling is insufficient. It is a design deficiency, or something has failed.

Oil jets contribute, so does ignition timing too advanced. Do you have electronic ignition? If one side, you can fly on one ignition source at a time and see if the temps are drastically changing with one or the other. Mine takes a while to have oil temps respond, so if you do this be patient, or just look at CHT's as the indicator.

On cooling, it appears you have a pacific cooler 9 row, that should be enough cooler, so it could be getting less air than needed, vernatherm not working properly, or plumbed incorrectly.

On enough air, in an absolute context, it would depend on the upper cooling chamber pressure (over the engine) compared to below the engine. How are the CHT's are they nice and cool? If so then you probably have enough pressure across the engine. Data may be needed, but this is a guess.

Airflow balance: if the CHT's are low then the air could be restricted to the cooler. It appears the scat is 3", if so it might be too small. Just adding a bell mouth inlet can increase the airflow by 20%. [As Toolbuilder notes below, the pressure drop of the scat length is proportional to its length, less inlet/exit losses]

Lots of things to check, so gather some data and post as you progress.

I might check, timing first, then check plumbing, and gather some temps to evaluate the duct size. Duct size seems to be a little small. Also is the diffuser on the cooler sealed tightly? Are there leaks?

[Toobuilder]

In addition to the diameter of the duct, also consider length. That duct diameter might work at 4 inches long with no bends, but your setup is really taxing delivered airflow. Long, bends, and SCAT = problems... Improve any and all of those factors and you should see positive results.

[F1R]

You have lots of good advice already. I can add that that the location of the duct in the aft baffle appears to be a bit low. If this is the case you are taking air that is essentially pre heated by the #4 cylinder fins, before it ever starts it's journey to the oil cooler.

Take a look at recent posts on Plenums in the engine section, note how high on the aft baffle the air is taken that feeds most of the oil coolers.

There was also a recent post in the RV 10 section with some good photos.

[DanH]

The four previous posts are all spot on.

Adding to Bill's advice, blowby can also be a major contributor to high oil temperature. Is it blowing much oil mist out the breather tube?

To put numbers to the "scat intake too low" note...even with the scat intake mounted as high as possible above the rear cylinder, I have measured 15+F temp rise between OAT and the remote cooler face. If the cooler air is flowing through the rear cylinder fins, it will be more.

Do I see some finned area of the cooler not covered by the small plenum?

[thompsonbr87]

Awesome, thank you guys for the insight! Headed out tomorrow with a friend who knows RVs well. We'll get to work on these suggestions. I'll update this thread with whatever progress we make.

[Toobuilder]

Something not cooling related caught my eye- it looks like the cooler is hanging off the firewall with a pair of L brackets, each attached to one ear of the cooler. If that's the case, I'd expect that kind of cantelevered, asymetric load to eventually crack the cooler either at the ear or right through the end tanks. A diagonal brace picking up the free end of the cooler would go a long way towards making sure that doesnt happen. Short of that, make sure you get eyes on it every time the cowl is off.

[rjcthree]

I just went through this. Screened 3” scat fed off the back of #4 to a 9 row AC standard cooler, firewall mounted. It cools a O320H2AD, which does not have squirters, but pushes more oil to the heads, and heat into the oil. I was running 215F in 65% cruise at 75F OAT. I started with screen removal, worth a few degrees, going to 4” scat, worth a few more degrees, then to the 11 row HE AC version of the SW, which got a solid additional 20f or greater reduction, so now I’m staying below 190F in all cruise modes - 188F at 82F OAT. WOT climbs stay below 205F at Vy now. My CHT got more consistent and about 5F less, and #4 is right in the middle, based on about five hours running this combo. In my case I went big, the HE cooler may have been overkill, but it was to be my fourth iteration, and I needed to be done. I may have to block it in winter, don’t know yet. I’m running Shell 15w50 semi synth year round at the moment. The cowling is stock outlet, no louvers or additional vents, it’s an -A model. No significant blow by, greater than ten hours per quart oil consumption, 100LL. Vernatherm work well. YMMV, good luck.

[FasGlas]

I guess this goes without saying but I'll say it anyway... Make sure your instruments are reading correctly. Always a good idea to check your readings against another instrument to make sure you're chasing a real issue.