Oil Cooler Structural Failure

[NWade]

Hello All,

Tragedy struck today shortly after starting my AeroVee Turbo. Through 6 short engine runs it had provided smooth and strong power, hadn't leaked oil, and the only sign of anything non-optimal was that I could only get ~36" MAP at WOT (but it was still making over 3000 RPM with my Prince prop).

On this run, I started the engine and got it idling for no more than ~5 seconds when my observer yelled "Oil! Lots of Oil!" I shut the engine down immediately and climbed out of the cockpit to see a HUGE puddle of oil below the airplane, and oil dripping from every item forward of the firewall.

After getting out the oil-dry and spreading it beneath the airplane, we started looking at the flow path of the oil around the crankcase to find the source of the problem. There were no obvious cracks, broken items, or loose hoses. But a bunch of the oil seemed to originate around the top-mount oil cooler itself. On a hunch, I double-checked that the mags & coils where off, then I slowly turned the prop by hand. After a couple of blades, a gob of oil burped out the front of the oil cooler - from somewhere between the first and second plates, down low on the pilot's side. I waited until the cooler stopped "drooling", then slowly pulled the prop around another 90 degrees of arc. Sure enough, another thimbleful of that green Brad Penn 20w-50 oil oozed out of the front of the oil cooler and dribbled down onto the crankcase.

After putting on my thinking cap while I spent 2 hours mopping up the worst of the oil in the engine compartment and scrubbing oil-dry around on the airport's asphalt, I've come to the conclusion that I probably got a bad part from CBPerformance. The other likely explanation is that my oil pressure is a lot higher than I thought, and the system can't take that much pressure. According to my VDO gauge, the oil pressure has been ~90 psi cold (air temps around 42 degrees F), with the pressure dropping to 50 psi once the engine has been running for 2-3 minutes. This seems a little bit on the high side, but not excessively so (unless my gauge is way off).

• Has anyone else ever experienced this failure?
• Does anyone have a recommended cleaner/degreaser that won't damage the insulation on the electrical wires in my engine compartment?
• Anyone have a way to get oil out of the exhaust wrap?
  (My guess is that I'll have to remove it and buy new stuff, as a couple of sections are absolutely saturated)
• Have a proven/approved method of slightly lowering the oil pressure in the AeroVee?
  (Cut the spring on the oil control plunger? Get a different spring? Something else?)

Thanks,

--Noel
(...who's not looking forward to removing the fence baffles and some of the wiring and the intake system and the aeroinjector to clean it all off)

[lutorm]

Wow. At least it happened on the ground!

I've heard of VW oil cooler failures due to overpressure, but they have been to the ones mounted in the "full-flow filter circuit", ie our bottom-mounted cooler. Since these are mounted before the pressure-relief valve in the case, they will see whatever pressure the pump is capable of putting out, which if the oil is cold can be very high (and does not show up on the pressure gauge since it is mounted after the filter.)

But it sounds like this is a top-mounted cooler, which should be after the pressure relief so shouldn't ever see those unregulatedly high pressures. (Unless your pressure relief piston is stuck, which would be a good thing to check.) Did you happen to record oil pressure data on this very run? 90 psi is a lot higher than what we had on our bottom-cooled Aerovee at "cold" (ie, 75F...) starts before I tore it down, but with gigantic bearing clearances and complete flow through the oil cooler bypass this engine still saw ~70psi. 90 should not blow a cooler, I'd think, so maybe it was a bad cooler. It seems easy to get VW parts of questionable quality....

An easy way to lower the oil pressure is to switch to a less viscous oil. In the auto world, not many seem to run 20w-50 in their VW's. 10w-30 seems much more common, certainly if the temperatures are down near freezing. Maybe since we run the engines at high power for long periods of time maybe they run at higher temperatures than in cars, so more viscous oil is warranted?

[rizzz]

90 PSI is very high,
I think I get mid 60’s to low 70’s cold and mid 30’s hot.
Definetly check the pressure relief pistons, they can get stuck and if you find it is, GP has instructions on their website somewhere to get it out.

[Area 51%]

Have you identified the type of failure yet? Thin material? Bad seam? Seal failure?

While dry-fitting my oil cooler to the engine, I noticed that the cooler was contacting the engine case bolt boss under it.

[marsolgp]

Noel, I had the exact same failure last year.... Makes a pretty good mess, huh?... My oil pressures run about the same as yours...... just chocked it up to another bad aftermarket VW part. I removed the cooler and blocked it off with the bypass plate and flew the rest of the 'winter' season that way. Don't really need a cooler in the winter.

[9GT]

No help here with your oil cooler but something that REALLY works well for de-greasing and is safe for your wiring is Super Clean available at most big box stores including Wal-Mart. https://www.walmart.com/ip/SuperClean-T ... 3=&veh=sem
Comes in a purple jug in various sizes right down to a squirt/spray bottle. Don't confuse it with Purple Power which is lame in comparison. Once you try Super Clean you'll want to keep it on hand at all times.

[NWade]

Thanks, all!

For the record, and to answer some of the questions:

An easy way to lower the oil pressure is to switch to a less viscous oil

The only "approved" oil for the AeroVee Turbo is Brad Penn 20w-50 Racing oil (semi-synthetic). :-/

Definetly check the pressure relief pistons

I'll do that once things are cleaned up; but when assembling the engine I made sure that the slugs slid smoothly up and down in their channels with just a bit of oil on 'em. But I guess that once they were installed with the honkin' springs behind them, they might have gotten jammed... Will investigate and report!

Have you identified the type of failure yet? Thin material? Bad seam? Seal failure?
While dry-fitting my oil cooler to the engine, I noticed that the cooler was contacting the engine case bolt boss under it.

No, not yet. The failed area is between two of the horizontal plates, somewhere back from the "leading edge" so its not visible. I've brought some parts home - including the fialed cooler - to try to drain and clean them. I'll see if I can find the exact point of failure once its cleaned up. As for my cooler, it never contacted the crankcase once it was mounted on the adapter plate with the oil seals in-place.

Will be calling Sonex momentarily to also get their opinion, and will report my findings here if there's anything noteworthy.

--Noel

[lutorm]

Thanks, all!
The only "approved" oil for the AeroVee Turbo is Brad Penn 20w-50 Racing oil (semi-synthetic). :-/

Indeed. I don't think there are any "approved" methods of lowering the oil pressure... ;-)

As long as you have sufficient oil pressure on hot idle, a less viscous oil is unlikely to cause a problem. (Some people even say higher-viscosity oils run hotter, because the increased viscosity leads to increased oil cooler pressure and more oil bypassing it.)

[kmacht]

Carefully with what you clean it with. Make sure it is safe for aluminum and use lots and lots of water. I like simple green but it has to be the one for aviation. The regular one found in home depot isn't good for aluminum.

Keith
#554

[NWade]

Just for completeness:

I got a somewhat-brief response from Sonex today. Basically I was told that I can run a lower viscosity oil, but they have no suggestions/recommendations on what to put in. They also recommended I put in a mechanical oil pressure gauge to cross-check the VDO sender (the VDO sender I bought from them. The one which maxes out at only 80 psi, so you can't truly tell if you're seeing excessive oil pressure). They also noted that I can run without an oil cooler in cold temps (but no comment on what temp range might be recommended for that mode of operation, or how I would go about modding the AeroVee to do this). They also recommended I idle the engine until the oil temp is above 80 degrees (which, of course, is exactly what I was trying to do when the oil cooler blew out).

:-/

Not being incredibly impressed with the depth of information I'm working with, I also read a bunch and posted on some VW forums. Many VW automotive solutions & standards are inappropriate for an aircraft applications. However, I wanted to see what they had to say and then make my own judgments based on my experience so far with the AeroVee and with automotive (racing) engines that I worked on in my youth. I got some great responses and some pretty useless responses (hey, its the internet). The two notable things I took away are -
(a) 20w-50 is claimed to be "too heavy" by many VW folks and has been known to blow out oil coolers. This is due to a combination of the stock oil galley size around the oil pressure relief plunger (which tries to bypass the oil through bearings and other narrow orifices), the heavier-than-stock oil-pressure-relief springs that come in modern VW kits, and the thick cold oil itself. AeroConversions undoubtedly has a reason why they want a thick oil in the engine (either to maintain high pressures with hot oil at high RPM, or to retain a thick oil film when the engine is not used for weeks at a time, or for some other reason). However I had my ear chewed off about how 20w-50 is excessive and unnecessary in an automotive application.
(b) Early VW oil pumps were smaller than modern pumps and the bigger aftermarket pumps people use now often require (or are heavily encouraged to use) oil pump covers with special pressure-relief passages, or remote bypass valves that are daisy-chained to remote oil filters. I find this info germane since the AeroVee Turbo seems to be using something similar to this CB Performance pump and I believe that pump flows more than the old 26mm stock unit.

So, here's my current plan:
(Note that I don't claim to know that these are the correct steps to take; just putting it on-record as what I am going to try)

1. Clean everything with Simple Green Aircraft Cleaner
2. Get a replacement oil cooler
3. Switch to Brad Penn 15w-40 oil (still semi-synthetic with high ZDDP). VW automotive guys are encouraging me to switch to 10w-30 but I want to make incremental changes and not suddenly find myself dealing with low oil pressure when the engine is hot.
4. Replace the 80 psi VDO sender from AeroConversions with a 120psi or 150psi VDO sender. I might lose a little bit of precision, but doing this will allow me to see if the engine is running up to excessive pressure levels on engine-start without having to run an oil line into the cockpit and set up a mechanical gauge.
5. Pull the oil control and oil pressure relief plungers out and check the bores for signs that the springs are scraping or not moving freely. I don't think this is an issue but I want to check to be sure. I tested the plungers themselves before assembling the engine and they slid smoothly and freely so I know they're OK.
6. Optional Bonus Fun - I'm really not a fan of the hard-line for oil that runs from the pressure sender to the crankcase flywheel flange. I'm going to look at converting that to a -4 AN braided hose and using an cushioned (Adel) clamp on the oil cooler attachment bolt to hold the hose in the proper orientation/shape (so it has a high point for oil to drain back, and so its own weight doesn't apply a torque on the fittings to loosen up over time).

--Noel