Oil Pressure Problem-1990 Q45 replacement engine

[Q45denver]

The shop that recently installed my replacement engine on my "90 Q is scratching their head as to why the engine loses oil pressure. They have replaced the oil pump, oil relief valve, and related oil chain components with no change in the oil pressure problem. I already advised them of the importance of properly torquing the crankshaft pulley. The master tech working on the engine had several years experience with Infiniti. The pressure builds up when revving but quickly drops off to the point were the oil light comes on. I'm about ready to write it off but they think it is still salvageable. The engine was very clean, runs strong and reportedly only had 50K miles. It also has good compression but the valves are noisy when cold. It had the guides replaced at some point and still had some broken guide pieces in the pan. The oil pickup screen was intact and no pieces were found in the pump and no metal in the pan. Any ideas would be appreciated since the local Infiniti dealer has no solution.

[maxnix]

Too easy to suspect the torqueing of the main crankshaft bolt, but it sure would explain slipping at higher rpm and loss of oil pressure. Have they torqued one before?

I assume from your explanation, the oil pump was disassembled and inspected and measured? If not, maybe a new oil pump is required.

[911/Q45]

A strong possibility is that guide pieces are still in there somewhere that clog a passage at higher sustained rpm. Alternatively, it ran with guide pieces clogging the oil pickup in the past and sustained damage then. Have they measured oil pressure with a gauge under various conditions?

[Q45denver]

The shop just called and said that after running the engine again briefly, the oil turned black and now it has good compression. Curious that it would all of a sudden clear up like that. I probably ran it a couple hundred miles at all speeds since I got it back from them without any darkening of the oil and they said that there was no sludge. I'm still concerned about damage that may have occurred running without oil pressure. Should I have them check any of the clearances? I'm not sure if any meaningful tests can be done without taking the pan off again.

[911/Q45]

If the oil pressure is good at idle when hot(measured, not just light off), then you can probably be confident it's OK.

[maxnix]

Well, I would say there is bound to be sludge in the oilpan. That is what crankcase flushes like Envirolution are meant to extract. I always have to add an extra ½ quart after a flush because it is so sucessful at extracting all the lubricant relative to a gravity drain.

The other thing I would be worried about is circulating pieces of the missing chain guides getting lodged somewhere. Why the entire broken guide must be found when pieces are removed.

The HLA noise might be a good clue as to what is occurring internally. Maybe the sound will be less at idle when warm, now. Don't confuse with injector noise.

[Q45denver]

The shop has pulled the oil pan twice and claims that there is and was no sludge and that all guide pieces have been removed. They have replaced the oil pump, oil relief valve, and related oil chain components with no change in the oil pressure problem. In addition, the old pump did not show any wear. Recently the engine started getting good pressure at idle (40 psi) for some unknown reason but it still does not build pressure when revved. They said that the the Infiniti dealer has no solution and they have checked and double checked the torque on the crankshaft bolt. Not sure if it is related, but they said there was a fuel smell in the oil.

[DAEDALUS]

When they pulled the oil pan did they bother to check the bearing clearances? Any chance the pump's sucking air in through the pick-up somewhere? There would probably have to be a noticeable volume of gas in the oil to affect pressure that much.

[Q45denver]

No, they haven't checked the bearing clearances yet which makes me question their competency since they have had plenty of opportunities and reason to do so. They are assuming the lack of metal in the pan, no visable wear, and good compression means that the engine is ok. They said the pickup was ok and the screen was intact. The pressure improved slightly when they changed the oil and filter again but it still drops off when you rev the engine.

[maxnix]

The pressure improved slightly when they changed the oil and filter again but it still drops off when you rev the engine.

Then there has to be a malfunction in the return galleries.

[Q45denver]

Then there has to be a malfunction in the return galleries.

Any suggestion for retifying with the engine in the car-engine flush?

[maxnix]

Well, there's the Delvac diesel change routine (add ATF just before change), the BG Quick Clean, and the Envirolution crankcase flush.

I like the Envirolution in that is goes in the reverse direction, so maybe blockage could be cleared.

One thought would be to put one of those remote filter adapter plates on the oil filter mount on the engine block and check the pressure there. Or even just install a clear high pressure looped tube and see if the oil is circulating at all rpms.

Are they reading the pressure mechanically at the oil sensor fitting?

Let me study the oil lubrication system in the manual. Seems like both return galleries would have to be blocked to get no oil pressure at higher rpm.

Q45tech, where are you?

[Q45tech]

I record the oil pressure in 15 second increments vs rpm vs coolant temp from crank till warm up [~~10 minutes] then drive on interstate until the oil warms up to peak another 10 minutes then do a few WOT runs [to peak heat the oil then piull off, then idle [in drive = worstcase low rpm oil pressure].

Transfer the data to a graph and study.

Obviously different brands of 10w30 will have different viscosities at different temperatures.

[Q45denver]

Thanks for the tips-I'll run them by the tech today. Any chance of cleaning the galleys by hand using those flexible gun cleaning rods. Yes, they get the readings mechanically at the oil sensor fitting. The tech (who is master ASE and worked for Infiniti for several years) was unaware of that the fittting was BSP 28 thread vs. NPT 27 however, he says the gauge fits tight and was not forced.

[maxnix]

The tech (who is master ASE and worked for Infiniti for several years) was unaware of that the fittting was BSP 28 thread vs. NPT 27 however, he says the gauge fits tight and was not forced.

Aaaaccccckkk!

[DAEDALUS]

Heh. NOW there's metal shavings in there. I don't think oil return could be the problem. Nothing complex about it. Oil just returns to the pan under gravity's influence. No small ports to get clogged. Feed lines are tiny, but if they were clogged oil pressure would increase.

[Q45denver]

From what they tell me, the pressure is between 40 and 50 at startup and idling cold and drops to about 30 psi once warmed up and stays there regardless of rpm. This is with 10w30.

[maxnix]

That would seem sufficient, and damn good for idle. How is it at redline or say 6K rpm?

[DAEDALUS]

Yeah, so what's the problem, besides the pressure being too high, (which is somehow causing the oil light to come on)?

[Q45denver]

The problem (according to the shop owner who is also the tech working on the car) is that the pressure still does not go over 30 PSI regardless of RPM and seems to drop off when you rev the engine. I noticed when driving the car that the oil light was coming on once the engine warmed up and it made a lot of noise when cold. That was over a month ago and they really haven't done anything since then other than change the oil and filter. I still need to record some more readings at various speeds as recommended by Q45Tech but there is an obvious problem with low pressure since the light was coming on and the valves were so noisy. Do you think I can safely drive it with 30 PSI?

[DAEDALUS]

I wouldn't, but really I'm more concerned by the seemingly flawed information. The oil check light is not RPM-dependent. If the light is coming on, it's because the oil pressure is dangerously low, ~3psi, not 30. Yet, 30psi at hot idle (as reported) is ridiculously high.

[maxnix]

I wouldn't, but really I'm more concerned by the seemingly flawed information.

Me too. This is screwier and screwier. What's the real story, besides the stripped threads on the oil sensor port? How does OEM sensor thread back in.

If you have no oil pressure at high RPM, then I presueme the HLA would create a racket that would be sickening. I am confused, or they are.

[Q45denver]

Ok, I'll try to be a little more specific this time but since I have not driven the car in over a month some of the details are a little foggy. All I had to go on when driving it was the oil light and the noise. The oil light did not come on until operating temp was reached and the HLA did not quiet down until operating temp was reached. The shop attached a mechanical Snap-On gauge in lieu of the sensor after I towed the car back to them a month ago and found no oil pressure. I am in the process of installing an electronic gauge permanently which is how I found out about the thread. Apparently there is not enough difference in the thread count that the NPT fitting had to be forced in. Is there some kind of sealant that I could use on the sensor threads that would not effect the ground to the sensor? They said their gauge only screwed in part way so the thread further back may be ok.

About a month ago when they tested it there was no oil pressure at any RPM up to about 2500 RPM. The idle pressure improved to about 30 PSI about a week ago for some unknown reason (see my post 4/6/05) after the shop changed the oil and filter and now the HLA is no longer noisy but pressure still does not go up when revving the engine and actually seems to drop off. Their current readings show no more than about 30 PSI at any RPM except for that initial spike when they start the engine when it goes to about 40 PSI. That about where they left it. They don't believe that a motor flush will do anything. I plan to look at it Friday and will get more specific readings at various operating temps. I guess the next step would be to pull the pan again and check the bearing clearances and see if there are any damaged seals or o-rings. Their initial tests indicate that the bearings and rings are ok.

[DAEDALUS]

You can use plain RTV, but wow, it's not easy to completely degrease the oil pressure port to ensure a good bond. The sensor will ground just fine, if not, then the threads are completely gone and you've got a big problem. RTV is a sealant, not a structural adhesive.

[maxnix]

Still sounds like an impropoerlly torqued crankshaft bolt. But I'll let other, more knowledgeable members diagnose this VooDoo engine.

[squeefoo]

Is the oil pan pushed up onto the sump? The checkball in the relief valve could have a piece of guide in it, the spring could be bad.Looked at mine today and the relief is accessible from outside just ahead of the #1 header pipe w/a 1" or so wrench. Pull the FP fuse and turn it over catch all the oil (and hopefully crap) in a totally clean pan, look in it with a mirror and blast away with brakleen. It's worth a try.

Edit: I had an Olds 350 seize up right after I installed it because the junkyard set it down too hard and pushed the pan up, it was barely noticeable.

[Q45denver]

Is the oil pan pushed up onto the sump? The checkball in the relief valve could have a piece of guide in it, the spring could be bad.Looked at mine today and the relief is accessible from outside just ahead of the #1 header pipe w/a 1" or so wrench. Pull the FP fuse and turn it over catch all the oil (and hopefully crap) in a totally clean pan, look in it with a mirror and blast away with brakleen. It's worth a try.

Edit: I had an Olds 350 seize up right after I installed it because the junkyard set it down too hard and pushed the pan up, it was barely noticeable.

Thanks for the tip, but I don't think that it since the engine had the same problems with oil pressure prior to them swapping over the oil pump, oil relief valve, and pan from the old engine even though the parts they replaced were undamaged.

[Q45denver]

Just an update on the situation. I went to check on the car and get some pressure readings however, after running the engine to get it to operating temp it developed a rod knock so it looks like a writeoff. I wonder what the record it for the most engines in one car? Latter I went to look for engine number four at the local wrecker. All had rod knocks and the wrecking yard owner said it was very common in the Q45's.

[Jesda]

Very rare. Very, very rare.

[DAEDALUS]

Maybe common in that neck of the woods from going to the same "master tech".