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High Oil Temps RV-8

R

RFazio

Well Known Member
My buddy has an RV-8 with an IO-360 angle valve engine, 200 HP. His oil temps are constantly high, even in cooler outside temps. Today when it was hot out we got up to 235 degrees climbing out and I couldn't get it down till I was at 6,500 and throttled back then it came down to about 210. He's got what he calls the bigger oil cooler on it with the standard RV mount on the back of the baffles. No door, wide open. My RV-6 is never hot always runs cool, and I have to close the door in the winter. We can't figure out why he's running so hot. We did change the varitherm, think that's what it's called. In the back of the engine. We check lines and the cooler to make sure they were clear. Looking for any suggestions, guys.
 
RFazio said:
My buddy has an RV-8 with an IO-360 angle valve engine, 200 HP. His oil temps are constantly high, even in cooler outside temps. Today when it was hot out we got up to 235 degrees climbing out and I couldn't get it down till I was at 6,500 and throttled back then it came down to about 210. He's got what he calls the bigger oil cooler on it with the standard RV mount on the back of the baffles. No door, wide open. My RV-6 is never hot always runs cool, and I have to close the door in the winter. We can't figure out why he's running so hot. We did change the varitherm, think that's what it's called. In the back of the engine. We check lines and the cooler to make sure they were clear. Looking for any suggestions, guys.
Click to expand...
There’s a lot of things to look at.. are the oil lines -6 or -8? How are the baffle seals? Anybody test the temp gauge to check accuracy? Some guys here go as far as a cheap Amazon manometer to check Delta P in front and behind the cooler. The IO-360 tends to run hotter oil temps because the engine has piston squirters that heat up the oil more..there are also different brands that some are more efficient than others..I’m sure someone here will chime in with their favorite.
The thing in the back, called a “Vernatherm”, that is like a thermostat for the oil, when it gets hot, I believe it expands and plugs a hole, making the oil go through the oil cooler circuit.
 
Tom, thanks for replying. So, yes, we tested the gauge. It was off by 20 degrees or so on the hot side. When it red lines at 260 degrees it's really 240. I'm giving you the after the adjustment temps. The vernatherm, we changed, and it made no difference. I thought that was going to do it, but no such luck.
 
RFazio said:
My buddy has an RV-8 with an IO-360 angle valve engine, 200 HP. His oil temps are constantly high, even in cooler outside temps. Today when it was hot out we got up to 235 degrees climbing out and I couldn't get it down till I was at 6,500 and throttled back then it came down to about 210. He's got what he calls the bigger oil cooler on it with the standard RV mount on the back of the baffles. No door, wide open. My RV-6 is never hot always runs cool, and I have to close the door in the winter. We can't figure out why he's running so hot. We did change the varitherm, think that's what it's called. In the back of the engine. We check lines and the cooler to make sure they were clear. Looking for any suggestions, guys.
Click to expand...
Start here:
My Process

I'm in the middle of similar issue, mine haven't been horrible but warmer than I like in So. AZ summer. Angle valve a bit of a different animal and much harder to cool so baffling and oil cooler more in play than for me with parallel valve IO-360. My CHTs are good pretty much regardless of OAT so this was yesterday:
  • I tested GRT OT temp probe/EIS and found it is reading 9 degs. low at 225 and 4 degs. low at 140, not what I had hoped for but useful data.
  • I tested my vernatherm (ECI 90 deg adapter) and it expands fully but quite a bit late/hot. It is definitely not in spec and I suspect there's considerable bypass.
  • I have fallen out of love with vernatherms in general and this one in particular and rather than play the $350 lottery to get a better one I'm going to get rid of it.
Will be ordering the viscosity valve plunger and spring tomorrow from Spruce. Phase 1 is bye bye vernatherm (I'll reduce it to just a plug) and install the viscosity valve. Phase 2 hopefully won't even be needed but when things turn chillier I may have to add the ball valve / cockpit control on the oil cooler line. If Phase 1 is not effective then Phase 2 is likely aft ducting on my engine mount located oil cooler.

I can provide much more detail if you want (I have loads of data including from a custom recording manometer and temp probe Arduino I built) and happy to share results once I have some.

Hope this is useful.

George
 
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George,

Wow, thanks for all the info. I’m going to be reading through it. Good to know I’m not the only one having issues.
thanks again and I’ll keep you posted.
 
I had trouble with high oil temps also on my non-RV. Installed the viscosity valve; it significantly helped. With the viscosity valve, oil starts cooler at the base of your climb so it's cooler at level off top of climb. In other words, you don't have a vernatherm heating your oil before you takeoff, then the cooling system struggling to maintain the desired temp.

I didn't see mentioned above, but other issues may cause high oil temps. Significant blow by can heat oil by allowing hot exhaust gas into the case; perhaps check compression. Advanced timing can cause high CHT, and in turn high oil temps also.
 
I'd be curious as to what he's calling the "bigger oil cooler". That engine requires more oil cooling because of the squirters. Are there any air obstructions to the oil cooler fins? Hose sizes has been mentioned as well. What are his CHTs running?

As a side note, I'm wondering how you guys tested that sender to 240 degrees. Are you pretty confident the test was valid? I've heard of people testing them with hot water, which is pretty difficult to get over 212 degrees.
 
D-Dubya said:
As a side note, I'm wondering how you guys tested that sender to 240 degrees. Are you pretty confident the test was valid? I've heard of people testing them with hot water, which is pretty difficult to get over 212 degrees.
Click to expand...

Speaking just for me I tested the vernatherm and sending unit both in fresh W100 oil in a cast iron pan on a hot plate. I'd bring it up to temperature and then record on the descent, typically about 3 mins for every 10 deg or so.

George
 
Vernatherm test information here:

Oil baffle and oil temps

So every Fall I attach an aluminum plate to the backside of my oil cooler to try and keep the oil temps up. It seemed to work ok though the temps were never very high. I would take it off in the Summer. But once off, the temps rarely got above 180 degrees. Usually more like 160. This Spring...
vansairforce.net vansairforce.net
 
I have similar setup on my RV7. I do have a plenum and mounted the cooler on the back side of #4 cylinder per Sam James himself as he is local.
First flight had to be terminated due to extremely high oil temps. The problem was two fold. First it was the seven row cooler supplied in the firewall forward kit and I don’t think that is a large enough cooler for oil cooled cylinders that are on angle valve engines.
Lastly, my plenum is a very low profile, and there wasn’t enough of an opening since the back side of the cylinder is blocking a lot of the airflow to the cooler.
I ended up installing another 7 row cooler in series and mounting it in front of number 2 cylinder, under the baffling and cutting an opening in the forward baffle, and now I get 190 on oil temp. I am Flying out of Florida, so even on hot days it stays under 200 during cruise. i can climb out at Vy to 8500 and temps stay under 200.
 
Measurable Success!!!

I'm very happy to report I did the first post-maintenance / post-mod flight, 28 mins, this morning and oil temps are considerably better. I'll post more in the near future since I believe I can provide some useful data to support the "ditch the vernatherm" strategy. For now:

  • 90 OAT on ground at 2400', 80 OAT at 5000' over airport
  • Oil only got to 150 deg before takeoff, big improvement
  • Oil barely got to 190 on climb, hit 205 for just a sec at best power at 5,000', didn't climb back above ~200 deg until on the ground and taxiing, hit 211 deg at shutdown after some slow flight in the pattern for traffic but it stayed below 200 deg

Compare that to a much longer flight two weeks ago with somewhat cooler OATs:
  • 80 OAT on ground at 2400', 70 at 8500 first cruise alt, 60 deg at 11,500', 65 deg at 10,500'
  • Oil got to 170 deg on ground before takeoff
  • Oil got to 222 deg on climb, leveled at 215 deg at 8500', hit 222 deg reaching 11,500', settled at 205 deg (other than short bit on descent) after that for the 3 hour flight leaned aggressively to minimum fuel flow at WOT, 208 at shutdown, no real pattern time

In short, I'm ecstatic. I'll hook my DIY pressure / temp recorder back up and fly a longer flight or two, then post some more data along with details of my engine/oil cooler/cowl/plenum setup.

George
 
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