8 92N low oil pressure after new bearings and oil pump

My starboard engine had small amount of metals in the oil analysis and also had lower oil pressure than the port side. We changed out the oil pump and bearings and everything else looked good so stopped there. Bearings were showing slight wear problems. After starting again the oil pressure seemed unchanged and at temp and on start up was running around 10-12psi about an 8 degree difference from the port engine. We checked the oil pressure gauge with a manual gauge and it was reading the same. We did not change the oil pressure relief valve as it appeared good during an inspection. We are not sure what to check at this point but maybe go back inside and change out the relief valve. Any other ideas since now we are going back inside or better yet a test we can do so we don't need to go back inside?

Hi,
Sorry you're having trouble.
Yes, it was probably a mistake to ignore the pressure regulator when the pan was off. These engines actually have two lubrication oil pressure control valves. One is a "relief" valve and should be set to dump at aroun 105 PSI.
The other is a "regulator" and keeps the pressure from building past 55 psi under normal operation.

Obviously the "regulator" gets the most work and would be the likely suspect in this case. But, a leak could develop in the "relief" valve and cause this symptom.

Were good measuring practices observed during the bearing swap? Plasti-gauge checks?

I'm sorry to tell you but it is probably one or the other. Either you got the bearing clearances too large or it is one of those regulator valves dumping pressure back to sump.

The two regulator valves are identical in every way except the spring inside. The "regulator" is on the left side of the oil pump (looking from rear of engine) and the "relief" valve is on the right.

I hope this is what you were looking for but probably NOT what you wanted to hear.

Good luck.

ALWAYS a good idea to check, clean and pressure test oil coolers if that hasn't been done in a while. The cooler could be a cause for low oil pressure (see trouble tree below) But a properly fitted oil filter should trap most debris before the oil enters the cooler.

Something else that could be checked if not done already would be the pick-up tube and screen. A clogged screen or a crack in the pick-up tube will affect pressure by starving the pump. And, since your pressure didn't come up at all after rolling in new mains, I suppose that should all be checked as well. Here is the "trouble tree" for low oil pressure directly from the 92 manual:

OIL:
Check for suction loss. Wrong viscosity

POOR CIRCULATION:
Cooler clogged
Cooler bypass valve not functioning properly
Pressure regulator not functioning properly
Excessive wear on crankshaft bearings
Gallery, crankshaft or camshaft plus missing

OIL PUMP:
Intake screen partially clogged
relief valve faulty
air leak in pump suction
pump worn or damaged
flange leak (pressure side)


I'm assuming the metals found in the oil sample were of bearing material? Copper, lead, zinc, tin? And not so much iron and chromium? Were there any markers that might explain the wear? Anti-freeze%, fuel% high? Low TBN ?

Detroit Diesel has always recommended AGAINST the use of multi-viscosity oils and only allow it's use in cases of extreme cold conditions. However, even then, their preference is for SAE 30 or 40wt. oils with block heaters. Just throwing that out there in case you were not aware of the "controversy".

As for the metals: iron 35 norm 22 was the highest then copper 8 norm 7, iron 3 norm 2. No trace of fuel or anti-freeze or contamination found did not do TBN. Oil Velocity was good. We found evidence on some of the crankshaft bearings that had metal had been stripped away the other bearings had slight wear. I use 40wt Mobil which is one Detroit recommends.

No, the Cooler has not been serviced for some time so we will do that, too. The oil pick up screen and pipe were clean (no trace of clogging or damage).

Can the Cooler just be cleaned along with the bypass valve?

I'm not sure I completely understand the question. I suppose you could "backflush" the cooler core and call it clean but I wouldn't count on it.

I will say though that, in my opinion, it would be unwise to go to all of the effort to take the core out to clean it and not have it pressure tested. In my experience, many that have been in service for a while have failed pressure tests and that would be a really "inconvenient" failure while in the engine.

When I was rebuilding these regularly, it was my practice to replace the core and the oil control valves with new along with the oil pump. And, even then, my shop would do a cursory pressure test of the NEW oil cooler core to ensure a ZERO comeback/warranty environment.

I will see about cleaning and pressure testing the oil cooler. Can a radiator place do that?. Here in La Paz, Mx not a lot of choices to take to. What pressure reading should they be getting or just checking for leaks? I was also advise to drop the cap on a few of the Camshaft bearing to see if after running an hour or so any other damage occurred.

Yeah, working on these big engines is not easy without a full blown shop. Pressure testing the cooler all depends on what type of cooler is fitted. If you have the "plate type' it is relatively simple to fabricate a test plate from a piece of sheet steel 3/32" or thicker. If it is a tube type cooler...not so easy. They both should withstand 150 psi but I was comfortable using 90 psi. and being confident that it would reliably hold in service. And, yes, I would think any decent radiator repair shop should be able to handle testing the coolers. Just make sure you question them on how they go about it. A good shop will answer all questions without giving you "attitude". A shoddy shop just wants your money...no questions asked.

About all you could do to get an idea about cam bearing wear would be to pull one of the end bearings. The intermediate bearings are inaccessible without removing the camshafts. While it IS possible to remove the cam gears to get to the rear bearing assembly, it is not all that easy. Getting them off is one thing and putting them back on is another. They are typically removed still attached to the camshaft. Cam timing MUST be maintained if you go in there so, aligning the timing marks and then locking everything down so that it can't move is crucial. You may be able to get the front bearing off for inspection a bit easier but that is going to be where the LEAST amount of wear is and might not yield reliable information about what is going on and what may be leaking.

I think that if you don't find a plugged cooler causing the low pressure then finding the leak could be very difficult trying to do it in a piecemeal fashion. There are plugs in the oil gallery that back out sometimes and only a tear down and block service will solve that problem. Forgotten or loose plugs have ruined many a rebuild.

I wish I had more encouraging news for you. About the only other thing I can think of (and I am NOT the sharpest tool in the box) would be to run a load of 50wt oil and see if the pressures come up. If they do, then at least you will know that it IS probably a bearing clearance problem somewhere and maybe an overhaul is in order. If the pressure stays the same, then it is a pretty significant leak and will absolutely need to be addressed.

We just finished cleaning and testing the oil cooler there were no signs of metals inside and the pressure tested good. We did replace the crankshaft bearings and upper/lower connecting rod bearings. We plan to do a final inspection of the #4 &#5 crankshaft bearings as they were the two that showed the most signs of wear before we replaced them. If no metals are found we will just replace the pressure and relief valve then close up the lower motor and cross my fingers we don't have to go into the camshaft. My mechanic also mentioned it could be damaged piston pin & bushing leaking. Thanks for your help.

One thing that caught my attention is that you say you...

"did replace the crankshaft bearings AND UPPER/LOWER connecting rod bearings".

This may be a silly question on my part but did you replace the UPPER/LOWER mains? You're not saying you just replaced the lower main shells... are you???!!!

Like I said, might be a silly question but I have to ask. Because if you didn't "roll in" new uppers, there's your problem.

Nawwww...couldn't be....could it?

And, I do hope you are doing your due diligence and checking all final clearances with Plasti-Gauge? Yes?


And, yes, it could be piston pin seals but I think if you have replaced ALL the bottom end bearings and you replace the pressure regulator then you've done pretty much all you can do without an extensive OH.

The pistons and even the cam bearings, to some extent, are "controlled leaks" in as much as pressure is intended to be released at those points for lube and piston cooling. Also, piston pin seal leakage large enough to affect oil pressure would typically be accompanied by plenty of blue smoke and excessive oil consumption.

I do hope a new regulator gets it fixed for you.

just wanted to get back to report that my starboard engine seems to be running well without the low oil warning coming on. But now the port is experiencing problems after replacing 3 fuel injectors. The engine warning alarm is going off at idle and when running at higher RPM the RPM gauge is jumping. Could this be a fuel issue? The oil analysis showed fuel in the oil so that is why the mechanic put in 3 new fuel injectors as last tune up(one year ago) those 3 seemed to work fine but we replaced the other 5-injectors with new ones. An oil change was done at that time, too. After noticing the fluctuation in RPM, I treated my fuel as it had lots of growth in the racors which I thought may be the problem. Racors were cleaned out and new filters put in also new fuel filter on the engines. Before running the engine I treated the fuel then transferred it through separate fuel transfer filters (on board) to polish the fuel before running through the new filters. I took the boat out and the problem still exists after running at speed for about 10 min. it starts to fluctuate again and does not want to run at low speed so the warning alarm goes off. Hope you may have an idea of the problem?