High oil temp

[6643]

Actually, I would be a pessimist, but there's no point in it...

[a64pilot]

My bet is someone thought stretching the spring would make it work better...

I tried counting the wraps, I believe there are a few more on the longer spring, maybe not, I didn’t think of a stretched spring, never entered my mind.
I used to build bikes at a race shop years ago, one of the hardest things was to get people to understand that the pre load adjustment on the shocks only changed ride height, it didn’t change spring rate or change the weight that the spring would bottom out at.
So if it’s a stretched spring it shouldn’t have caused pressure loss with increasing temp, it actually shouldn’t have changed spring rate at all?
I’ve only got one flight, tomorrow I’ll fly in the heat of the day again (many of us fly to lunch on Wed) So i’ll look again of course.

I guess it really doesn’t matter why so long as it works, but the drop of 10 psi pressure with 20 deg rise in temp I still can’t explain, has to be the relief valve being partially open due to a weak spring.
Now you have me wanting to measure the pressure it stacks up at, and compare it to a new spring, but the new one is in the airplane

[6643]

So if it’s a stretched spring it shouldn’t have caused pressure loss with increasing temp

I think it's the other way around. I expect the problem occurred, and someone tried to fix it by stretching the spring.

[a64pilot]

So if it’s a stretched spring it shouldn’t have caused pressure loss with increasing temp

I think it's the other way around. I expect the problem occurred, and someone tried to fix it by stretching the spring.

Do these springs lose their heat treat somehow? Think about valve springs, they go through what has to be billions of cycles, get hotter etc. once in a blue moon one breaks, but it’s exceedingly uncommon. Sometimes they lose height and have to be replaced at overhaul, but this spring should leave a very easy life by comparison.
I’ve never done it, but maybe this is a wear part that should be replaced at overhaul?

[a64pilot]

Todays lunch flight, OAT was 94F

[tonycondon]

So my oil pressure was also running on the bottom end of the range. With Oil Temp at 190 or so it took full cruise RPM to just keep it at 30 psi. I changed out the spring as mentioned here. The new spring is shorter than the old spring, just like here.

Today I had 52 psi on takeoff and 40 psi in cruise with 180 degree oil temps. Apparently the old spring wasn't holding tight.

[6643]

The new spring is shorter than the old spring...

Could be someone in the past stretched the spring in an attempt to increase the oil pressure.

[tonycondon]

I'm starting to think that at some point Continental changed the size of the spring.

I see other posts in the archive indicating that the shape and size of the plunger probably changed at some point.

It seems pretty obvious from comparing the TCDS, Owners Manual, Overhaul Manual, and other documents that Continentals opinion on the "normal" oil pressure range has changed over the years. Values range between 30-35, 30-40, and 30-60, at least. Maybe a 30-45 in there somewhere. And 100 max with cold oil.

[6643]

Not much help, but, as far as I know, the 60 psi limit only ever applied to engines certified under E-252: the C90 and O200. This may have something to do with the fact that some models were equipped for oil operated prop governors.

The most recent version of E-233 lists minimum 30 and maximum 40 for the C75 and C85.

I recall reading somewhere about a change to the plunger, but can't remember any of the specifics.

[tonycondon]

yes, the TCDS has a parenthetical reference to 30-40 psi in Note 1.

Overhaul Manual lists 30-60 psi for "normal cruising range" C75, 85, 90, and O200 in the Table of Specifications Section

Overhaul Manual lists 30-45 psi at full throttle in the Test Operating Limits section

The Owners Manual for A,C, and O-200 lists 30-35 psi as Normal with a Max of 35 psi for all operations, except a Max of 100 psi on run up with cold oil.

Later in the Emergency Section of the Owners Manual, it references 30-60 psi as the normal range.

Even later in the Owners Manual, it says that the Pressure Relief valve is set to give 35 psi. That is clearly not the case with the current springs.

So there are 3 documents that reference 5 different maximum oil pressure values. 35, 40, 45, 60, and 100.