Crank driven oil pump priming 3.9l

[Andypderrick]

Hey everyone

I’ve got a 3.9l V8 in my Marcos and have recently done an oil change. However on start up I have no oil pressure.

It has a remote filter so I have tried pumping oil back into the pump. Oil filter was filled on replacement. Still no oil pressure.

I took dizzie off to try the spin over of the pump gear but then discovered engine has the crank based oil pump so can’t prime it that way.

Any thoughts on how to prime it!

Cheers
Andy

[stevieturbo]

If priming is the problem...you could try removing the spark plugs to reduce load on the engine and crank.

Or on some problematic engines in the past that have struggled to prime, I've hooked up a vacuum pump to an oil gallery ( turbo feed, oil pressure switch etc etc ) and whilst cranking, pumped up to help try and suck oil up through the pump.

Or you could get an electric pump and manually prime the pressure side of the engine, oil galleries etc.

Have you actually started the engine ? or still trying cranking ?

[Andypderrick]

Engines starts fine just no oil pressure and I didn’t want to rev it to risk it !!!

[ChrisJC]

I would give it a quick rev. The Thor engine immediately revs to 1500rpm before falling back when started, and I do wonder if that is to ensure a prime on the oil pump.

Chris.

[Andypderrick]

Well i have tried about 1/2litre of oil throught the pressure switch opening and then fired it up, still no pressure (both light and gauge) any one got any other ideas short of stripping the front cover off. I might try removing the remote and fitting the filter direct to the engine. Seems a lot of work just to do an oik change.!

[SuperV8]

Well i have tried about 1/2litre of oil throught the pressure switch opening and then fired it up, still no pressure (both light and gauge) any one got any other ideas short of stripping the front cover off. I might try removing the remote and fitting the filter direct to the engine. Seems a lot of work just to do an oik change.!

This is the oil flow path for the crank driven oil pump.

Lubrication
The full flow lubrication system uses a gear type oil pump driven from the crankshaft. The assembly is integral with the timing cover which also carries the full flow oil filter, oil pressure switch and pressure relief valve. Oil is drawn from the pressed steel sump through a strainer and into the oil pump, excess pressure being relieved by the pressure relief valve. The oil pressure warning light switch is screwed into the timing cover and registers the oil pressure in the main oil gallery on the outflow side of the filter. Pressurised oil passes through an oil cooler mounted in front of the radiator to the full flow oil filter. The oil then passes through internal drillings to the crankshaft where it is directed to each main bearing and to the big end bearings via numbers 1, 3 and 5 main bearings. An internal drilling in the cylinder block directs oil to the camshaft where it passes through further internal drillings to the hydraulic tappets, camshaft journals and rocker shaft. Lubrication to the thrust side of the cylinders is either by oil grooves machined in each connecting rod big end joint face or by splash.

I think I would double check the fuel filter - sure its the correct one? some have internal bypass circuit - could be faulty?
Or pressure relief valve? make sure its free.

If you have used the correct filter and your pressure relief valve is working the crank driven oil pump should be self priming. As mentioned maybe try tickling the revs to help.

[ChrisJC]

Once upon a time I started an engine without realising that the remote filter was connected backwards, so no oil flow, but the oil light did go out.

Anyway, it ran for about 5 minutes before it started making odd noises.

Chris.

[stevieturbo]

Once upon a time I started an engine without realising that the remote filter was connected backwards, so no oil flow, but the oil light did go out.

Anyway, it ran for about 5 minutes before it started making odd noises.

Chris.

Problem is, with the oil switch on the pump, as opposed to in the engines oil galleries, the pump is pumping against the one way filter....the wrong way. So it does see pressure.

Not to worry....I did same and drove mine for about 5-6 miles. All things considered it wasn't that noisy....but it did end by breaking the crank into 3 pieces LOFL