918-S

I had a strange issue last fall that may or may not be serious depending on the answers I get here.

1980 euro "S" M28-11 bored to to 5.0 hybrid. I was driving very normally last fall on a cross country trip. I had been traveling for about 600 miles steady freeway speed. I pulled off the freeway for gas. As I started back on the freeway I noticed the oil pressure gauge drop from 90-100 psi to about 50-60 psi. the pop back up. Then drop again. Thinking this may be a loose sender wire I decided to get off the freeway and check it. About 2 miles from the on ramp there was a wayside rest. I pulled in. As I stabbed the clutch peddle I watched the gauge go from 40-50 to zero! Eeek! I shut off the engine and coasted into a parking spot. I checked the sender wiring and everything was fine. I cranked it up and the gauge jumped full up to 100 psi. but dropped off to 30-40 psi. Then I heard a lifter ticking so I shut it off and call AAA.

Anywho, has anyone ever had a pressure relief valve stick or fail? What are the symptom?

Any other thoughts before I have to tear into this engine again?

Mrmerlin

I would be inspecting the oil temp springs and pistons just above where the oil cooler lines fit

918-S

Thanks for the reply. What should I be looking for? The engine as about 5500 miles on it and I had fresh 20/50 oil in the engine when I left town so sludge shouldn't be an issue.

Do the springs fail?... get weak? Is that the failure to look for?

Mrmerlin

usually its best to just replace both of the springs and the pistons they are relatively inexpensive.
Also replace the thermostat and its spring under the oil pressure sender
If this doesnt cure the issue then you may have oil pump issues

918-S

Here's my arrangement. I had to move the sender up to the cooling line location. It ran into my shift rod. I also tapped the other line cap for a manual gauge in the event I had an issue with the electical gauge. That's what the small threaded plug is for.

I'm sending the filter to a forensic engineer to have it checked for metal. If it tests good I will purchase new valves and springs for the relief stuff.

I'm fairly sure I gutted the themostat. I'm not running a cooler so I don't think I needed the stuff.

Second question: Anyone ever had a pump fail?

I had a valve shim shatter and get into the pump once it locked the pump causing the timing belt to give out the most horrific scream you've ever heard!

I replaced the pump and drove the car about 3500 miles before tearing it down. I can't see what could go wrong with the pump other that the impeller coming loose from the drive shaft? I would think that would cause an instant failure.

928mac

You said you heard lifter noise.

Then it is not the sender but a lack of oil.

I would be pulling the pan and looking for a reason.

(I'm Guessing)-It could be a small crack in the pick tube or that something has come loose.

You need to look until you find why the oil pressure dropped. sorry

918-S

Ya, I think I'll start with having the oil filter checked for metal. That should tell if I need to look at bearings and do a full on teardown. I always had oil pressure but it dropped fast, bounced back up then dropped again. I only saw zero when I stepped in hte clutch and the engine dropped to idle.

I thought about the pickup tube coming loose also. I seem remember applying locktite on the pickup tube bolt... I have a photo of the bolt install showing lock tite on the bolt but I'm not sure which build the photo is from.. I assembled this engine a couple times.

928mac

Well in your defense, when I did my main bearings (last spring) I also maid sure that everything was tight and torqued and rechecked, but now that the engine is out for intake refresh I see 1 bolt on the side of the girdle has backed out.

Dam this means I have to go inside and recheck everything.

918-S

I just got the test resullts from the chemist. The oil tested normal. I'm relieved but still uncertain I am out of the woods. I hope to have time to dig into this further over the weekend. Here are the test results.