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Rallylancer122

Well Known Member
All,

I'm having some trouble with an RV-8, and unfortunately the original builder is no longer available to answer questions. I'm hoping the brain trust here can help.

What happened: I was flying across northern MN on Sunday morning when the oil temp ran away. It got into the 240's before a combination of drastically reduced power and rich mixture started it back down. Got it down in the low 220's when I had to duck 1000 feet to get below a cloud deck. That sent it back up again and further reduced power didn't help. EGT's and CHT's were fine, pressure fine, just temp. Luckily I was over Brainerd regional airport and landed uneventfully. Ambients were in the 80's already at this point.

What we did: Oil level was good, cooler was clear. We checked the sender/gauge with some oil in a can against a thermometer and it was accurate up to 220 where we stopped heating the can. We changed out the vermatherm and oil was going through the cooler and lines. (Oil cooler was nuclear hot when I landed, so I know oil was going through it...though I can't say for sure how much). We checked the sump screen and cut open the filter, no metal. Engine runs good, plenty of compression when we pulled the prop through, makes power. Finally we filled it with fresh Shell 100. Two test flights and the same result. The oil quickly skyrocketed past 230 (less than 10 minutes), and was in the 240's by the time I got it on the ground. Ambients in the mid to high 90's at this point.

Airplane: 1999 RV-8 with 2000+ hours. About 100 hours on a Barrett overhauled IO-390. Early Sam James cowl with 4.75" inlets. Lightspeed ignitions. Single Niagra oil cooler behind #4 cylinder. I failed to get the size and p/n (it was 98 degrees on the ramp...I just brain faded), but it was whatever Van recommended at the time.

I've only flown the plane about 20-30 hours, and never in ambients this high. It always ran around 220 degrees, which is hot, but it would stabilize there and I assumed it was just a result of big engine/tight cowl/quest for speed. I'm half thinking that oil cooler is just too small for that high of ambient temp, and that if I just wait for a cooler day I can probably nurse it home and put a bigger cooler on. But if that were the case then wouldn't reducing power have helped? (I was down to 19 inches and it still was climbing) Plus, the original owner flew nearly 1000 hours with this same setup, and never mentioned an issue at high ambients (not saying he didn't have it...just never mentioned it). Before I try flying it again, I want to make sure I've exhausted all options.

Thoughts? The airplane is currently stuck 7 hours (by car) from home. When I go back to get it, I need to go back with a solution.

Thanks,
DEM

PS. Any RV guys in the Brainerd area?
 
Welcome to the VAF forums! (ha! I beat Mike S to it)

If you're running a stock Niagara 7-row, baffle-mounted oil cooler on an IO-390 (presumably angle valve heads and piston oil squirters too) then your oil cooler is simply several sizes too small. A big engine of that much heat-producing capability needs IMHO, at least a 13-row oil cooler, and a cooler that big will need to be mounted on the firewall or on the engine mount frame and plumb some 4" SCAT duct to it.

EDIT: Once the oil has been cooked, it may have lost a bunch of its lubricating ability. You might try changing the oil and filter (* use Aeroshell 100W) before flying again. Don't run it a very long time at high power takeoff settings to keep the heat from building up too much at first and baby it home.... and obviously make the flight early in the morning as possible. Once the oil gets really hot... with an underpowered cooler, the temps won't want to come down easily at all once the engine and oil are heat-soaked.


*Back a couple years ago when we were having oil temp issues on a freshly built -8 with ECI IO-360, we found that running Aeroshell 100W Plus would get the temps down a fair amount better than 20W50, but ultimately it took a bigger, expensive SW oil cooler to handle Texas heat.
 
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This is probably no help, but heat rejection to the pistons are increased with timing advance. If you could retard ( or fix timing) to standard 25 BTC ( or your spec) then it might give some relief for a trip home.

Just a thought.
 
Dennis,

Wait for cooler OAT's and it will be like it was before - 220 or so.

That being said, if 220 was the norm before this event, it is running on max cooling which is not enough. As OAT goes up oil temp will follow degree for degree. If you were seeing 220 with the OAT at 65, it will go to 240 at 85 OAT.

An 0390 produces a lot more heat than a parallel valve 0360. This engine needs more cooling capacity - IMHO - no matter how long it was run as is.
 
Like Bill, sudden onset leads me to suspect a timing issue. I'd theorize that you couldn't control temperatures because the reduction in MP further increased timing advance, and the speed decay reduced airflow. Per the LS manual, you should see idle strobe light readings of 35? ? 2? when the manifold pressure hose is connected and 16? ? 2? when disconnected.

http://www.lightspeedengineering.com/Manuals/Plasma_CdiManual_20130317.pdf

Even prior to this problem you needed a larger cooler. A Meggitt (Stewart Warner) 8432 two-pass or a 10599 single pass (same physical size) would be the minimum.

I recently installed a ducted 10611 for my 390, but run it with a variable area cowl exit much smaller than stock. The 10599 was marginal in hot conditions with an exit under 40 sq in (stock is about 60). Marginal in my wee mind is 200-210F.
 
Hi Guys,

Thanks for the great info! Hadn't thought about the timing. Not sure why it would suddenly change, but easy enough to check. Assuming that's ok hopefully I can nurse it home on a cooler day and then upgrade the cooler.

If anybody else has some thoughts, it will be a while before I can get back there so feel free to chime in.

BTW, if you are going to get stuck at an airport, there are worse places than Brainerd, MN. The local FBO was very helpful loaning parts and tools, and the airport got me into a hanger.

Thanks,
DEM
 
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