Does anyone have thoughts on why oil temp would (suddenly) steadily build?

Motor is fully built and has been running for ~4.5 yrs with no concerns on oil or water temp. Occasionally, oil temp would go up to 210-215°F. I have taken on many long trips (several hours, hundreds of miles).

Recently, I changed the intake and have had an issue with a sticking throttle. It has several times gotten into the rev limiter (currently set to 6800) due to the sticking throttle issue. Now just driving for ~15 minutes, I will see oil temps that are in the high 230 range. I have not continued to drive beyond the 230+ range because I am concerned with damage. But for all intents and purposes, it appears like the oil temp would keep climbing.

I have changed the oil and filter (using Castrol dino-lube and Performance filter). Water temp seems to run in the 190-210°F range as it is hot in S TX area.

Performance seems to be on par (except I cannot tell a whole lot with the current throttle sticking issue).

Any and all comments are welcome.
Aaron

 

Any change in oil pressure behavior?

Did you do a visual on the oil & drain plug. Any chance that
the filter is still in the trash?

Any discernable difference in engine noise?

.

 

Actually, oil pressure has changed because of the change to the new "cleanable" filter on the '87 vette. But the higher oil temps were there before I changed the oil and filter. I cut open the old Fram filter, and it was clean inside. The oil drain plug has a magnet and it was clean as well. The oil was slightly brown, but nothing unusual. It had probably been in the car for ~6 mos.

There seems to be no difference in the engine noises.

One thing I did have to do was grind a bunch of clearance into the "T" that mounts the (I believe) oil psi switch and ignition (or fuel) cut out switch at the back of the manifold. It would not clear with the Team G intake. But, I can not see how that would affect oil temp.

I am stumped.

Aaron

 

Read my mind. Your circumstances behind your increased temps sound like mine. I ran my stock L98 (88 w/ a 120K miles) up to 6200 during a bad day at the track. I had done no outward or audible damage to the engine but my pressure went from 26 to 28 PSI at a hot idle in gear to 19 or 20 PSI. I upped the oil to 10W-30 and I got some of my pressure back. My temps are now out of control and my pressure is back down to 19 or 20 PSI even with the heavier weight oil.

My oil does not cool off and the temps just keep climbing and it does so quickly, even in normal driving not working the car at all. I haven't torn it down but it has got to be bearings in my case.

 

Does your car have the separate engine oil cooler? I wonder if there is some sort of thermostat on the oil line to the cooler that is not operating properly. I know that when Chevy introduced the LT1 in '92 they did away with the cooler and switched to synthetic oil (Mobil 1).

 

The oil psi has been pretty consistant before and after. However, when I switched to the new "cleanable" filter, my oil psi went from being 18-20 psi at idle to ~30 psi at idle. It gains roughly 10 psi per 1000 RPM (same as before, just ~10-12 psi higher due to the new filter, which is expected).

I am interested in the bearings comment as to how an overrev suddenly made the bearings go South. If the bearings went S, then what is happening to the oil that is causing the higher oil temps?

I have though about the oil cooler issue. Mine has the oil cooler/heater that has a large coolant loop that goes fwd from the water jacket and then returns coolant to a chamber just above the oil filter. I wonder if there is a thermostat in there that routes coolant through the oil cooler when the oil temp gets so hot? Could it just be coincidental that the cooler plugged following the intake install? I could fairly easily pull the cooler and take a look at the thermostat if it exists.

Many thanks for the replies, and keep the ideas coming.
Aaron

 

If RPM got ahead of the pump's ability to lubricate, then the journals
could have touched the bearing surface(s). Bearings are designed to
sacrifice themselves in such an event, but this results in more clearance.

More clearance means it is harder to maintain the proper oil film
between journal & bearing. In such a scenario, things begin touching
increasingly often. Friction causes heat which the oil picks up as
it passes through.

(A separate scenario where oil heats itself is where it is being
compressed and recirculated in the pump by-pass circuit. Not
applicable in the present situation, I believe.)

My vote is that clearance has opened up on one or more mains.
IMO, mains make less noise for a given oversize than rod bearings
do.

Others may have different suggestions regarding causality for the
oil temp rise.

Incidently, what oil pan was in place?

.

 

I had a bad feeling when the pressure almost immediately dropped and I kind of figured it was one or more bearings. My suspicions were confirmed when I added the heavier weight oil and my pressure went back up, until of course the oil got good and hot.

Slaloms explanation certainly seems plausible, especially in my case. Now that the clearance is opened up there will be more contact with the crank and bearing surface, causing an even greater clearance and higher temps, with bearing failure being the ultimate end result.

The increase in oil weight was a very temporary band aid. I've gotten maybe 200 miles out of it and things are quickly heading south. I am interested to hear some other explanations but in my (limited) experience these symptoms point to the first signs of bearing failure on one or more mains.

 

To answer some of the questions.

I run the Canton extra capacity (side kick-out) oil pan. I run a hi-volume, low psi oil pump. I haven't really noticed any decrease in oil psi, just the increase in oil temp. After the addition of the cleanable oil filter, the psi did increase, but the temps seem about the same.

My car has hit the rev-limiter (6800 RPM) many times in its life, but in this case, the throttle was hung and it just hung at a higher RPM. I do not think that it actually hit the rev limiter, I think it just had my shift light (6200 RPM) steady on. I thought I had hurt the motor, so I killed the ignition at probably something very close to 6200 RPM.

As a side note, the water temps seem a bit higher now but I am not positive on this, as I really have not been able to drive for extended periods of time at cruising speeds.

I appreciate the resposes thus far.
Aaron

p.s. Upstate, how do you spin a stock TPI long tube intake engine to 6200 RPM? On my DD '88, you would be lucky to over rev to 4800 RPM.

 

Stuck in 2nd gear WOT, went through the traps at ~96 MPH. It wasn't making any power but it still spun that high .

 

 

A few days ago, I went and talked to my neighbor. He builds engines for a living.

He asked a couple of key questions.
1) Answer slowly how I arrived that my temps were not normal?
2) Was I certain what the temps were before the intake change?
3) Were my oil temps within 25° of the water temp and not exceeding 240°F?
4) Have I been able to drive the car like I was driving it before this happened?

He knows what parts I have in the engine (quality parts throughout).
Answers:
1) The oil temps seem to be increasing, but I really did not have a reference point, as answered in #2
2) Reality is I always run around with the oil psi displayed prior to the intake change. It happened that the car overheated directly after the intake change due to a failed primary fan motor (coincidence?). This overheating (230°F coolant temp) caused me to pay close attention to both the water and oil temp.
3) I drove the car this evening, and even though it was evening air, the coolant never exceeded 195°F and the oil temp stayed within 20° of the coolant temp, but was mostly within about 12° of the coolant. It helps to quantify problems.
4) I drove the car this evening like I did prior to the intake change. I actually went out and put ~15 miles on the car. City and highway driving. I have been so concerned with the throttle issue that I have been "putting" around at 20MPH, throttle sticks, then limp home. The throttle issue is (at least partially) fixed, so back to decent driving.

He reassurred me that shutting off the engine "against" the rev limiter, or backing off the throttle with it hung at 4500RPM is not going to hurt a fully built motor. He ssemed quite convinced that I had not hurt the motor.

However, he did confirm that steadily increasing oil temp is typically a main bearing exciting the performance.

I am happy, as all seems back to working right. Now back to tuning on this thing. It is "nasty" fast and quite scary at night!



Thanks for all of the opinions and input.
Aaron

 

Very glad to read that there appears to be no problem.

Thanks for the follow up.

.

 

Slom,
No problem. I think that all who start threads should include the final outcome. Otherwise the chapter isn't finished.

Upstate,
How about an update on what you found in your engine?

Aaron

 

I wish I actually had news to report. That would mean I had time to pull the engine and get to work on it.

This thread will probably be in the archives by the time I get around to looking into it, but I have it bookmarked just in case a miracle happens.