Still dramas with 1988 3CX - now engine oil pressures

[UnclejakeNZ]

I purchased and shipped the machine to the remote island I live on in April. The thing owes me a touch under $40,000 but so far it's only done 50 minutes work in six months due to mechanical problems and huge delays getting parts shipped. It's a non turbo Perkins engine.

The latest hassle was a sudden drop in engine oil pressure just after a head gasket change. I figured the mechanic hadn't properly seated the O ring that seals engine oil to the passage through the head to the valve gear, but that turned out to be fine. I'm using 15/50 engine oil.

I had 3psi at idle and ~ 20psi at working RMP so the machine got parked. We removed the oil pressure gauge feed line off the side of the block, cranked the engine over and barely a dribble of oil came out. To my mind that eliminated a faulty oil pressure gauge.

'Fast' forward nine weeks and I got delivery of a new engine oil pump, new pressure relief valve ... and (as the sump was coming off anyway) a set of main and big end bearings and the associated rod bolts, gaskets etc.

Mechanic #1 had had enough of working in a wet and windy paddock so enter mechanic #2. He dropped the sump, visually inspected the bearings and said they were perfect. He then replaced the oil pressure relief valve. The workshop manual says a non turbo relief valve should open at 60psi.

I now have 100psi at idle and 120psi at working RPM. The mechanic says this is fine but I'm too scared to run the motor as I really don't want to be replacing crank seals etc. The motor certainly sounds better than it did before the pressure relief valve change (less noise from the valve gear after a second or two from engine start)

First we need to find another oil pressure gauge to eliminate that, but if is a faulty gauge is not the problem I'm a bit confused. Any thoughts are welcomed.

[essexpete]

Would it be worth changing the oil for a different grade and the filter?

[gecko.cx]

For interest, I'd pull the old oil pump apart and measure it with feeler gauges to see if there was a problem with it (I'd assume the pressure relief valve was the problem, but it'd be nice to know).

Given your bearings were "perfect", I'd guess your current high pressure is only due to the heavy oil. A 10W/40 oil may be a better choice - you're not exactly in the tropics!

I've been looking at the manual and I can't see where the gauge is tapped in. Is it before or after the filter?

[UnclejakeNZ]

Hi gents, and thank you for taking the time to respond.

I neglected to mention two things:

1) The drop in engine oil pressure at idle occurred immediately after a H/G change. As part of the H/G change we fitted a new oil filter and new engine oil (it could have been 15/40 now you mention that geko.cx. I will need to check tomorrow.). I used the machine the day after the H/G change and notice that the engine oil pressure was too low. The first thing we did was change the oil filter which made no difference.
2) Neither the oil and filter have been replaced since. It is literally the same oil and filter that idled at 3psi, but now 100psi after the oil pressure relief valve was swapped.

For the avoidance of doubt: The original oil pump is still in the engine. We did not change it.

[gecko.cx]

I think there is no doubt the pressure relief valve was responsible for the drop in pressure (the 'why' is a different story).
A heavier oil (particularly at cooler temps) will raise the pressure (worth checking what is in there).
Given you've still got your original oil pump and the bearings are "perfect", it really suggests the rest of the engine will be in very good condition too.

You bought bearing shells, but were they fitted? The oil normally flows from the block, through a hole in the shell bearing (main), through a drill hole in the crank to lube the beg ends. If something went wrong (wrong bearings, bottom fitted to the top ???) it's possible to blank off the oil passage which in turn cause a rise in oil pressure. Not pleasant thoughts, but just trying to eliminate what can be eliminated.

[UnclejakeNZ]

Excellent point, and one I hadn't considered gecko.cx. A spun bearing could absolutely change oil pressures.... but in this case the only things we changed between the first low oil pressure issue, and now the too high pressure issue, were the oil filter and more recently the pressure relief valve. We did not fit the new bearings, but the mechanic only removed one big-end bearing cap for a visual inspection. He didn't remove any of the main bearing caps.

Personally, I can only think of two possibilities right now:

1) A faulty oil pressure gauge (doesn't seem all that likely given the differential between idle and working RPM has stayed largely the same @ 20psi) but a crook aftermarket gauge can't be eliminated yet). I also need to look at the oil circuit to confirm if the pressure is read before or after the filter, but I am 85% certain the pressure is read before the filter. TBC ASAP sir.
2) Faulty brand new JCB oil pressure relief valve (after removing the original faulty oil pressure relief valve).... which also doesn't seem that likely as 2 x faulty relief valves (with totally the opposite symptoms) in a row (after changing the HG) seems like really bad luck!

I'll check what exact oil we used tomorrow night

[UnclejakeNZ]

Here she is getting unloaded from the ship on Chatham Island in March 2023 after $5k of urgent portside work as they wouldn't let her onto the wharf due to massive hydraulic system oil leaks... but the blown head gasket, flogged out steering, seized side-shift, 100% of bulbs blown (including the dash), cracked dipper arm... and a handful of other items were issues I didn't know about until she came off the ship.

I was excited then. Not so much now! LOL

[mechman]

uncle jakenz, Did you fix the side shift problem? Mine has the same problem,
Norm

[UnclejakeNZ]

uncle jakenz, Did you fix the side shift problem? Mine has the same problem,
Norm

Yes mate. We soaked the doughnut shaped clamps with penetrating oil and then beat them hard with a mallet. The impact loosened the rust bond and the side shift now works.

[UnclejakeNZ]

Sadly a borrowed oil pressure gauge shows exactly the same (very high) engine oil pressures as the original gauge.

The sump will come off again. I also partly dismantled the old oil pressure relief valve and the spring seems fine. Perhaps it has a damaged seal on the piston as I couldn't get the piston out on the kitchen table. I guess it'll need a blast from an air compressor.