Oil Pressure Confusion

[WesRagle]

Hi Guys,

I've been having "issues" with the Oil Pressure of the GPAS 2100 engine I've been using for development of the VeeCU.

The oil pressure starts out OK but decreases rapidly as the oil warms up. As a quick fix I bought an adjustable plunger and installed it on the flywheel end of the engine. I bumped the oil pressure up but the oil pressure still decreases too fast as the oil heats up. Well, I got impatient and cranked it up too high. You can probably guess what happened.



Yep. I need to install a new oil cooler.

The thing that has me confused is why, pray tell, does the pressure decrease so rapidly as oil temperature increases. Also, the oil temperature never gets very high. Here is a screen shot of the oil pressure and oil temperature during a recent engine run.



You can see that with an oil temperature of 142 the oil pressure is already down to 32 at 2500 RPM. This is with the adjustable plunger at the same setting that burst the oil cooler at start up with oil temperature at about 7 Deg. C.

Since the oil temperature never reaches a good running temperature, maybe I should increase the pressure on the other relief plunger. Maybe that would also provide some protect for the oil cooler.

Not sure where to go from here, except to back off the flywheel end plunger.

Suggestions appreciated.

Wes

[peter anson]

What oil are you using? It's a long time since I ran a VW engine so I don't remember what is recommended. Is a multigrade OK?

Peter

[WesRagle]

Hi Peter,

Brad Penn Penn-Grade 1 Racing 20w50. Semi Synthetic. I had it left over from break in of my Hummel 2400.

Wes

[peter anson]

OK, no great suggestions for you. I had a similar problem on an earlier aircraft powered by a VW based engine, but in my case the oil was getting much hotter than that, and cured by forcing more air through the oil cooler. One very slight possibility - check the accuracy of the oil temperature sender. I assume the temps are in degrees F?

Peter

[WesRagle]

Peter,

Yea, I'll check the sensor. I't does register correctly at ambient. The temps are in Deg. F. I only said 7 Deg. C. because the engine hadn't run in a couple of days and I walked past a thermometer that read 7 Deg. C.

I have never studied the oiling systems of VWs in detail. I started looking at that but haven't reconciled what I have read with what I see.

First things first. I put off cleaning up the mess all day. I'll take care of that tomorrow. I have an oil cooler that came with the Hummel but I didn't use it. I'll see if that will fit.

Thanks,

Wes

[bvolcko38]

In my long experience of buying almost junk cars and trying to keep them running, it sounds like a bad bearing. Check your oil and screen or filter for metal.

[WesRagle]

Thanks Bill,

I'll check. I also need to set the valves. I've put about 50 gal. of fuel thru the engine since I changed the oil. A lot of starts and low RPM running with cold oil.

Wes

[WesRagle]

Hi Guys,

Really nothing of note in the screen. A few flecks of yellow paint from the case.



Wes

[Dave Wolfe]

Wes,
You may get more response to this question on HBA the VW knowledge is extensive over there.

The best I can tell the oil valve near the pulley end diverts oil flow to the oil cooler when the oil is thin and low pressure. When cool and high pressure the oil is bypassed thru the valve and does not go thru the cooler. So it does not work directly thru oil temperature but rather indirectly thru pressure as the viscosity and resulting pressure depend on temperature.

[kmacht]

32psi is actually pretty good at 2500 rpm. The general rule of thumbs on aircooled vw engines is 10psi per 1000 rpm. The adjustable plungers are mostly just a bandaid and rarely fix pressure issues. Have you inspectex the oil pump? If the clearances between the cover plate and the gears gets excessive the pump will lose pressure as the oil thins and it seeps past the gears.