Oil Cooler Structural Failure

[Sonex422]

I also have had an oil cooler failure last spring right after I converted to a top mounted oil cooler. It occurred during initial run-up and leak test. Initially I thought it was high Oil pressure because of the 90 psi reading on my MGL Stratomaster.

On examination of the failed oil cooler it was discovered that there was a poor weld between the corrugated fins and the chamber containing the oil.

After replacing the top mounted oil cooler and before starting the engine again I bought a direct reading test gage from Harbor freight with a long hose. After engine start it read in the normal 50 psi range. So I did some more research and found out that the MGL stratomaster defaulted to Rotax settings (probably should have done that earlier). Rotax uses a 200 PSI VDO gage. So I simply had to set the correct scaling factor in the Stratomaster. Once completed, the readings matched that of the test gauge. There have not been any oil system issues since then.

I hope that this may help.

[NWade]

On examination of the failed oil cooler it was discovered that there was a poor weld between the corrugated fins and the chamber containing the oil.

...So I did some more research and found out that the MGL stratomaster defaulted to Rotax settings (probably should have done that earlier). Rotax uses a 200 PSI VDO gage

Thanks! Yeah, my Discovery Lite iEFIS defaulted to a 100psi gauge, and on my initial engine start I saw 100psi during the first few moments of running. Later on I realized I needed to adjust the EFIS and set it to the 80psi range of my VDO sender. From then on, I saw 80 psi during the first minute or two of each engine run. But I think my oil pressure may well be higher than that; its just beyond the max that the VDO sender can read. I'm curious to see what reading the 150psi VDO sender shows me on startup; if I can't get a good consistent set of readings from it then I'll grab a direct-read gauge from HF and see.

Either way, I'm making these series of changes just to be on the safe side. I'd hate to clean this mess up and then blow _another_ oil cooler!

--Noel

[daleandee]

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).

When I had my VW powered nose roller I was returning back home from my second time flying to the ASA meeting in Crossville Tn. I was coming down the valley and had just crossed over into Georgia when I noticed the oil pressure at 80 PSI. At first I thought it must be a bad sender and then I considered that there might be a few people in the graveyard that thought that too. Straight ahead about 11 miles was Dalton (DNN) so I decided to land there and find out what the problem was. After landing I took a look at what I could see without pulling the cowling & did a run-up. Everything was absolutely normal. Unicom had called and asked if I needed assistance. I told then the concern but all seemed well and I was taking off but depending on how it went I might be right back. It never did that again ...

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.

I'm in the camp that believes that 20W50 may be too thick. While it's true that air-cooled engines have larger clearances & tolerances change more because they run at a higher temp, oils are much better than they used to be and oil that is thick can't flow well. Pressure is important but so is flow. The factory says they want to see something above 40 PSI on the engine. Then builders get into thinking if 40 is good then 50 is better! So they tend to set the oil piston spring pressure higher & use a heavy oil and at start up on a cold morning the oil pressure can really shoot up high if the engine has to be spun up to keep it running in the cold. Resist the temptation to set the pressure too high or use oil that is heavy. I like your approach below about trying a viscosity oil that is one step below what you are currently running. I use 15W40 Rotella and it works well but I rarely will be flying if the temps are near freezing. (I'm turning into a wimpy old geezer).

My Corvair engine uses a stock factory oil cooler. We generally test them to 80 PSI before using them. You might consider doing that ... even with a new one. If your oil system is correctly set up you won't need a sender that reads over 80PSI. If it's reading that high, how high it is is not really a concern but getting the airplane on the ground is!

With your experience you are aware that they make an Oil Pressure Adjustable Pressure Regulator so you can set your oil pressure where you want it. As the engine breaks in you can reset it if needed.

Dunno if this helps,

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
166.7 hours / Status - Flying
Member # 109 - Florida Sonex Association

Latest Video - "I Wanna Fly" https://www.youtube.com/watch?v=1VP7UYEqQ-g

[hollandvw]

Hi guys and gals The factory vws from the 70's I.E. 1600 dual port (wich your engine is based on) recommended 10w30 in the winter and straight weight 30 in the summer changing bore and stroke has no effect on the oiling system or passages. I am not an expert but have built well over 50 vw engines in the 35 years I have been working on them and would never use anything but rotella 15w40 in the summer and 10w30 in the winter even on my turbo street engines. 20w50 in the winter has to be about like pumping 80-90 gear lube in the summer. Also I have never run a synthetic in a Aircooled vw as synthetics are designed to reject heat and 40% of your engines cooling comes from the oil. hope this helps Scott

[NWade]

Today I found out the hard way: mentioning 20w-50 on certain VW forums will get the sanctimonious a-holes there raging! *sigh*

Dale - I wasn't aware of an adjustable pressure regulator for the VW; I'd be curious to see what that product looks like - have any links or product names I should look up?

My understanding (after dealing with some actually-helpful folks on the VW foums) is that the outflow of the oil cooler connects back to the main oil galleys, and there are no check-valves in the system. Therefore, even when the oil pressure spikes and the oil relief plunger opens up, the oil that bypasses the cooler still routes through the bearings and galleys and the end result is that the entire oil system still pressurizes. With no check-valves, oil can be forced to backflow up into the cooler until it reaches the same pressure as everywhere else. You get no real flow through the cooler; but you do get pressure in there.

Aftermarket VW folks have designed oil pumps that have pressure-relief ports that dump oil directly back into the sump, but those solutions are not usable on an AeroVee Turbo because of the double-stacked oil pump design we use.

Take care,

--Noel

[daleandee]

I wasn't aware of an adjustable pressure regulator for the VW; I'd be curious to see what that product looks like - have any links or product names I should look up?

https://www.ebay.com/p/EMPI-9198-VW-Bug-Adjustable-Oil-Pressure-Regulator/1974594347

Aftermarket VW folks have designed oil pumps that have pressure-relief ports that dump oil directly back into the sump, but those solutions are not usable on an AeroVee Turbo because of the double-stacked oil pump design we use.

I haven't seen what Sonex is using but I have a '74 Beetle with an Auto-Stick that has a double stack oil pump. They are stacked together but are separate in their operation as the outer one is used to drive hydraulic fluid (Auto trans fluid) for the torque converter part of the Auto-Stick transmission setup. It really is a pretty good German design. Here's a link to the VW pump:

https://www.evwparts.com/vwparts/113115101A.html

Dale Williams
N319WF @ 6J2
Myunn - "daughter of Cleanex"
120 HP - 3.0 Corvair
Tail Wheel - Center Stick
Signature Finish 2200 Paint Job
166.7 hours / Status - Flying
Member # 109 - Florida Sonex Association
https://www.youtube.com/watch?v=1VP7UYEqQ-g

[NWade]

I wasn't aware of an adjustable pressure regulator for the VW; I'd be curious to see what that product looks like - have any links or product names I should look up?

https://www.ebay.com/p/EMPI-9198-VW-Bug-Adjustable-Oil-Pressure-Regulator/1974594347

Thanks! On the one hand that's kludgy as hell; on the other hand its brilliantly simple. All that thing does is stop the oil control plunger from retracting all the way. So its good for helping keep the oil pressure higher. But sadly I can't see how it would help lower the oil pressure below stock/standard levels; so it won't help me at the present time.

Its good to know that exists, though. Thanks for sharing!

--Noel

[lutorm]

Thanks! On the one hand that's kludgy as hell; on the other hand its brilliantly simple. All that thing does is stop the oil control plunger from retracting all the way. So its good for helping keep the oil pressure higher. But sadly I can't see how it would help lower the oil pressure below stock/standard levels; so it won't help me at the present time.

I think it actually pushes the bottom of the spring up, changing the spring preload. But that still means you can't use it to lower your the relief pressure except by also switching to a lighter spring.

And about the pressure relief valve still pressurizing the cooler: yeah, the cooler will always see the indicated oil pressure. But that pressure will be set by the pressure control valve at the rear of the case, not by whatever pressure is needed to squeeze the oil through the cooler. It's the latter that can get really high, since the control valve will dump oil back to the sump if the pressure is higher than something like 35psi (I may be misremembering the pressure it relieves at.)

Edit: there is another situation that can lead to overpressure: if you use a 30mm or larger oil pump, the relief passages are apparently not large enough to relieve all the excess flow, so the pressure can spike to very high levels.

There's an interesting thread at thesamba here: https://www.thesamba.com/vw/forum/viewtopic.php?t=280293 where some guy took pressure readings at different places in the oil system for a bunch of different conditions. Really useful for understanding how the oil pressure behaves.

[Area 51%]

CB performance has the oil cooler block-off/bypass plate. The part number is 1733 and it's $17.95.

[SonexN76ET]

Noel,

I believe you may be over thinking the high oil pressure you experienced. Likely it is one of two things. Either your pressure relief plunger stuck or you had a defective oil cooler. Your’s is the only top mounted cooler I have heard of that has burst. Most Aerovee builders have the issue of trying to increase their oil pressure. Also as your engine starts to break in you will likely start to see your pressure come down and you will start looking for ways to increase your oil pressure. The device Dale wisely presented is a very commonly used solution.

Finally, in regards to oil, please disregard the advice from automotive VW experts who have never flown behind or operated or maintained a VW powered aircraft and rather follow the recommendations of the factory. The flying environment is completely different than the road environment. Flying stresses on an engine are more akin to driving uphill in a fully loaded truck on a steep grade with a constant heavy load on the engine and at relatively high constant rpm.

As a side note, I recommend you take Robert Hoover’s VW blog with a grain of salt. He was an enthusiastic VW hobbiest and someone with strong opinions who loved to write. He had nowhere near the experience of John Monnett, Great Planes, Hummel, or Rev-master. Some of his advice is bogus. For instance, his advice on painting VW engine cases does not work. I tried it and my paint peeled right off.

Jake