Author Topic: No oil pressure after new oil pump  (Read 272 times)

SammyS

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No oil pressure after new oil pump
« on: February 21, 2019, 09:12:22 PM »
If anyone would have an idea of what could be going on to cause my '92 SR to now have basically no oil pressure please sound out, as both me and my mechanic are completely out of ideas.

I bought a 1992 SR in December with 150k miles.  She ran great, only a bit of lifter clicking sound when starting on a cold morning.  Gave her an oil change and filter right off the bat (the seller had obviously recently changed the oil too, but I wanted to know exactly what was used and when, so).  I put in 5W-30.  Had about 20lbs of oil pressure at idle, 45-55lbs driving.

There was an oil leak from around the harmonic balancer, so I brought her in to my mechanic to change the timing belt, tensioner, new water pump, and to chase down the oil leak.  He did the timing belt work and replaced the shaft seal external on the oil pump.

Still ran great with great oil pressure.  But still was leaking oil.

Back to my mechanic for the oil leak.  Took everything apart again and this time removed the oil pump, discovered there was a small crack in the pump housing by the main shaft that was causing the oil leak.  He replaced the pump (with a Melling), put everything back together, and now no oil leak, but now the Montero is running with loud clacking lifter noise, and there is basically no oil pressure at idle (and not quite 30lbs driving).  Oil pressure sender reading verified with a mechanical gage screwed into the sender port.

Mechanic thinks "must have been a bad pump somehow".  I get an OEM pump and we go through the whole tear down again and replace the Melling with the Mitsu pump.  Put everything back together: still no oil pressure and loud lifter noise.

Mechanic loans me a Cherokee and tears the engine down again.  And now I'm going in to the shop too to investigate and verify things.

The three gaskets on the oil pump were all properly placed (pickup, filter adapter, block)

Oil pickup tube clear, no blockage.  Screen clear.  Pickup tube not cracked.

No metal shavings, bits, in the oil pan.

Pulled the connecting rod cap assembly and we check the main bearings- they look fine, no bad wear

Pulled the OEM pump, I just went over it today, took the cover off, nothing amiss in the gears.  Took out the pressure relief valve, looks fine and not jammed, no junk in there.  No blockage in any passageways as far as I could see carefully going over it w a pen-light.

Then I went over the oil filter bracket looking for a blockage.  No blockage anywhere that I could see.  Disassembled the filter bypass valve- looked fine, no gunk, seemed to operate fine.

I didn't blast air through the fittings (don't know how everything goes in my mechanics shop there and he was pretty occupied today), but visually I couldn't find any sort of gunk or blockage anywhere in the pump or filter bracket.

?????????????????  What on earth could be causing the no oil pressure ?????????????  Could something in the heads have popped and not allow pressure to build up?  Is there somewhere else a blockage could cause LOW oil pressure rather than high pressure??

Think the mechanic is going to have a look at the heads tomorrow, as we can't think of anything specific to look at.

Any more ideas?!
« Last Edit: March 17, 2019, 08:22:37 PM by SammyS »

rodmankn3

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Re: No oil pressure after new oil pump (out of ideas!)
« Reply #1 on: February 21, 2019, 10:25:21 PM »
was it primed when installed?

SammyS

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Re: No oil pressure after new oil pump (out of ideas!)
« Reply #2 on: February 21, 2019, 10:31:46 PM »
Mechanic says yes.  Although also I have been told by another tech that priming the oil pump is not an absolute necessity

was it primed when installed?

SammyS

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Re: No oil pressure after new oil pump (out of ideas!)
« Reply #3 on: March 17, 2019, 08:22:12 PM »
Postscript: On dis-assembly again my guy still didn't keep track of which oil pump bolts were where so nothing is certain, but after he and I disassembled and cleaned out every part from the oil pickup to the pressure sensor (pressure relief, cooler bypass, cooler lines, cooler, oil pump itself..)  he "discovered" on re-assembly that if the 55mm and 60 mm bolts are switched on the right side of the pump the 60mm bolt barely bottoms out in the 55mm bolt hole before the pump and gasket are firmly snugged against the engine.  If you're not paying attention you may (and his guy may have) think you snugged up the bolt properly and not see that the pump itself isn't snugged.  But since doing this fails to snug the pump against the engine block perhaps there is then leakage of oil down to the oil pan between the pump channel and the galley-hole in the block.  And this would explain how there was some oil pressure but below acceptable minimums (well below 10lbs at idle), even though there were no blockages in the system and the pickup was fine.

GrantCee

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Re: No oil pressure after new oil pump
« Reply #4 on: March 18, 2019, 03:42:16 PM »
Hope that solves the problem!

I pay strict attention to the bolt placement in the FSM. Mitsubishi was pretty specific about bolt lengths and where they go.