Oil Cooler Structural Failure

[lutorm]

Did you ever try the different viscosities? I just noticed that Great Plains recommends 10W-30 (or straight SAE30) for use with their Force One bearing.

[NWade]

Did you ever try the different viscosities? I just noticed that Great Plains recommends 10W-30 (or straight SAE30) for use with their Force One bearing.

Yes, I'm using the 10W-40 grade of Brad-Penn oil.

I will point out that in the end, my oil cooler failure was probably not caused by using 20W-50 oil itself; rather the root cause was the oil control plunger sticking at the top of its travel.

Still, I am remaining with the 10W-40 for now since I am getting good oil pressure (40-60 psi) out of it in my ground runs, the plane will live in an unheated hangar, I was not provided with any specific red-flags (beyond needing to watch my oil pressure) when discussing this weight of oil with tech support personnel, and VW forum enthusiasts continue to strongly recommend avoiding 20W-50 in conjunction with the larger/up-rated oil pumps that are found on the Turbo (although I recognize that their experience with cars may not be directly applicable to an aircraft engine).
In short: I don't believe it is likely to provide me much upside (other than occasional cold-weather operation). But I wasn't able to discern any major risks/downsides to using 10W-40, either.

--Noel

[lutorm]

Hmm... So I just got my Aerovee started after the rebuild (after some troubleshooting, see separate post) and I also have 90+psi (off-scale high) at startup idle. I'm even running Brad Penn 10W-30 for the moment. As the oil warmed up to 120F or so it dropped to the 80s at idle. I guess I'll be taking a second look at my oil plungers, too...

[NWade]

Hmm... So I just got my Aerovee started after the rebuild (after some troubleshooting, see separate post) and I also have 90+psi (off-scale high) at startup idle. I'm even running Brad Penn 10W-30 for the moment. As the oil warmed up to 120F or so it dropped to the 80s at idle. I guess I'll be taking a second look at my oil plungers, too...

Yes, I highly recommend doing so! That is almost exactly what I was seeing in my original situation. Good luck, and reply to this thread or private message me if you have questions or want further info on how I solved my issues.

NOTE: I want to reiterate that I recommend *not* using the specialty tool you can buy to extract the plungers. The little metal fingers that expand into the plunger can definitely cause the plunger to "bulge" against the interior passage and bind up even worse. If the plunger is stuck and simple methods don't get it out, use an appropriate-sized tap. That method was effective & straightforward, and new plungers only cost a couple of dollars online.

Good luck!

--Noel

[Sonex422]

Make sure that you double check your settings for the oil pressure sensor. I had a similar problem and determined that I used the wrong ratio (my MGL unit at the time had defaulted to Rotax settings which used a sensor with different resistance values). Your numbers look like they are twice that of the normal, same as mine originally. Correcting it solved my problem. I did confirm the umbers with an actual pressure test gage (harbor freight part).

Regards

[lutorm]

I think the pressure sensor is OK because before the rebuild we had ~45psi at cold idle. (And that was with 20W-50 oil, this is with 10W-30.)

[lutorm]

Soo... i took out the spring and cranked the engine and the plunger came out, no problem. I started it without the plunger and got about 50 psi at idle. As the oil warmed up to 60C, this dropped to about 15psi. I still had about 80psi if I opened the throttle, so even with the oil control valve wide open you seem to get quite a high pressure.

So now I'm unsure of whether the plunger was truly stuck or if that's just how strong the spring is... From what Pete212 said before, it seems he had a very high opening pressure for the valve.

[NWade]

Which plunger did you check?

[lutorm]

Which plunger did you check?

Both. The front came out with the spring. But I only ran it with the rear out because I wanted to isolate their effect on the oil pressure.

[lutorm]

Ok, after removing the sensor I see it says "0-5bar" on it. I believe is is this guy: https://vdo-webshop.nl/en/pressure-senders/378-vdo-pressure-sender-0-5-bar-1-8-27-nptf.html.

Now, 5 bar is 72 psi and the specs say this sensor maxes out at 184ohm. The MGL is calibrated for a 200ohm sensor with max pressure 145psi. I guess this means the oil pressure has always been half of what we thought it was... In recordings from before the rebuild the oil pressure when hot came down to 17 psi, so that means it was actually 8.5 psi, at 3000 rpm. No wonder the bearings were bad, that's really low!