Oil pressure drops to zero when warm

[Wintermute]

Okay, I know I haven't been on here in forever and a day...but I'm finally getting back to my m715. Still have an issue where the oil pressure once warmed up drops to zero and then starts running really rough.

On start and idle (until it really warms up, the old 230 runs at 30psi...revved it jumps to 60+). Once it runs for a while and warms up fully, it will start dropping a bit at a time until it hits zero pressure...when it drops to about 20, the engine starts to run pretty rough (shaking, uneven idle, and some knocking). When it first starts up it sounds and runs like a a brand new engine. Once the pressure starts dropping it's a sure path to zero. Running brand new 10w-30 in it with a nos oil pump.

Any ideas here? I wondered if the block has a crack, or if the timing chain cover gasket is shot and allowing oil to blow out of the through passage once warm. Anyone had this problem before and figured out what it was?

Thanks in advance,

--Wintermute

[Nailhead]

Okay, I know I haven't been on here in forever and a day...but I'm finally getting back to my m715. Still have an issue where the oil pressure once warmed up drops to zero and then starts running really rough.

On start and idle (until it really warms up, the old 230 runs at 30psi...revved it jumps to 60+). Once it runs for a while and warms up fully, it will start dropping a bit at a time until it hits zero pressure...when it drops to about 20, the engine starts to run pretty rough (shaking, uneven idle, and some knocking). When it first starts up it sounds and runs like a a brand new engine. Once the pressure starts dropping it's a sure path to zero. Running brand new 10w-30 in it with a nos oil pump.

Any ideas here? I wondered if the block has a crack, or if the timing chain cover gasket is shot and allowing oil to blow out of the through passage once warm. Anyone had this problem before and figured out what it was?

Thanks in advance,

--Wintermute

That says "worn-out engine" to me. A buddy of mine & former neighbor in the hills of SE Wyoming had an older F250 that would do the very same thing, to the point he put 90W in the crankcase. The oil pressure would be 50 psi cold idle, dropping to almost nothing idling hot.

You didn't mention mileage, but assuming it's high, I'd say time for a rebuild.

[jeeper]

My experience with low oil pressure when warm has been bearings that are worn out. Crank and/or cam bearings.

I currently have a 1997 Jeep TJ that drops oil pressure when warmed up. It sounds like a diesel engine when I first start it up because the lifters are all worn out too.

What I did to combat the problem short term is run 15w-40 oil. It doesn't thin out like 10w-30 does when it gets warm. Recently I've also had great success using synthetic 20w-50. That stops it from sounding like a diesel when it's cold and maintains 20 psi at idle when warm.

Ultimately my engine needs to be rebuilt/replaced. I have an engine that I have already rebuilt waiting to go in but the original keeps going and going so It has become an experiment to see how long I can make it last before I swap it out.

[Wintermute]

Well, trying to get a slight bit of life out of the motor while I assemble the 350chev I'm going to replace the 230 with. Ran seafoam in the crankcase, fuel, and ran a whole can of seafoam top end cleaner through it. Did an oil change (oil was clear before I did the seafoam...pitch black after). Started it up with the new oil after that and got about 1.5hr of run after warmed up before the pressure started to drop. Before all that, the pressure would start to drop as soon as it warmed up. Bearings are probably worn to death (89,000mi on the engine). Kinda wonder if a second (now capable of doing it longer) seafoam run in the crankcase would get me even longer run time.

--Wintermute

[Nailhead]

Well, trying to get a slight bit of life out of the motor while I assemble the 350chev I'm going to replace the 230 with. Ran seafoam in the crankcase, fuel, and ran a whole can of seafoam top end cleaner through it. Did an oil change (oil was clear before I did the seafoam...pitch black after). Started it up with the new oil after that and got about 1.5hr of run after warmed up before the pressure started to drop. Before all that, the pressure would start to drop as soon as it warmed up. Bearings are probably worn to death (89,000mi on the engine). Kinda wonder if a second (now capable of doing it longer) seafoam run in the crankcase would get me even longer run time.

--Wintermute

It might clean out the oil galleys, improving oil flow and giving longer run times, or it might clean out dirt in other areas that have been obstructing oil flow and boosting oil pressure to a certain extent, and have the reverse effect.

89K-- hell, what have you got to lose?

[jeeper]

I'd try the 20w-50 full synthetic. I'd be surprised if that didn't give you better results than the 10w-30. Since the engine is slated to get replaced you've got nothing to lose.

[kwai]

I run the 20w-50 valvoline high mileage oil in my worn-out sbc 350. It does improve the oil pressure.

I wouldn't waste my money on the full synthetic though. That's like buying a $50 bottle of wine for dinner with the wife when beer works just as well.