Oil Pressure 'sticky' - Defender Source
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  #1  
Old July 2nd, 2007, 04:22 PM
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Jason Herring
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Oil Pressure 'sticky'

Hi, I am having a bit of a strange issue with my oil pressure after having a whole bunch of work done to the engine (basically had it rebuilt the most expensive possible way, piece by piece). Included in this work was new bearings/rings and new oil pump 'kit' (housing was not replaced).

Each time the engine is started cold the oil light will do something peculiar - it will go off, then flash on then go off again. That was odd, but worse is that once in awhile the oil light will come on and just stay on - normally when this happens it will happen when starting up. Usually if I 'rev' the engine up a few times the light will go out and stay off - almost like something is 'stuck' if that makes any sense.

I changed the idiot light sensor and there was no difference in behavior.

So, I used the second oil pump sending unit port to install a mechanical gauge to verify what was going on. Because of the unusual 1/2-20 thread I had to tap a bold to NPT and thead in an adapter (worked well, actually).

Now I can see my pressure more exactly & have verified that when this somewhat random oil light on situation happens that the mechanical gauge is reading 0psi also. So...what could be causing such random behavior? And why would revving the engine up clear up the problem? The light will stay off at idle until I rev it anywhere from once to a few times - turning the car off/on does not fix the problem.

Obviously I'm not thrilled about revving the engine w/ no oil pressure! Incidentally, under high RPMs my OP gets to about 35psi max and at hot idle sits at about 14psi - not thrilling numbers, I'd like them about 5-7psi higher. I am running 10W40, will probably go to 15W50 or 20W50.

Any thoughts on what could be casuing this? My first thought would be something in the oil pump - that spring-check-valve thing in there perhaps.....?
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  #2  
Old July 2nd, 2007, 05:14 PM
MonLand
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Did you make sure the sender is clean (quite a few people have mentioned gasket residue and such stuck on the grill filter of the sender)? How did you prime the oil pump when you installed it?
I'd definitely not run this engine anymore unless you know for sure you found and cured the problem... 0 PSI definitely means either a blocage of some kind or a non-pumping oil pump.
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  #3  
Old July 2nd, 2007, 06:02 PM
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Mike Hansen
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I am guessing that it is an oil filter bypass valve sticking in the open position. Maybe you lost the spring behind the ball valve in the oil pump housing.

Thats my guess anyway.

MH
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Old July 3rd, 2007, 02:55 AM
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Jason Herring
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I changed the sender and also added a mechanical gauge.. it's accurate.

Most of the time the pressure is ok, but sometimes something 'wrong' happens and I get the 0 PSI situation...

Quote:
Originally Posted by MonLand
Did you make sure the sender is clean (quite a few people have mentioned gasket residue and such stuck on the grill filter of the sender)? How did you prime the oil pump when you installed it?
I'd definitely not run this engine anymore unless you know for sure you found and cured the problem... 0 PSI definitely means either a blocage of some kind or a non-pumping oil pump.
Follow-up Post:

A shop did the assembly for me. That sounds plausible to me - I will ask them to see if they are *sure* it was installed.

Does anyone have a photo of the oil pump, maybe an exploded view, I could show the mechanic to illustrate that?

Quote:
Originally Posted by mhansen
I am guessing that it is an oil filter bypass valve sticking in the open position. Maybe you lost the spring behind the ball valve in the oil pump housing.

Thats my guess anyway.

MH
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  #5  
Old July 3rd, 2007, 08:36 AM
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I had a customer that had a very small "burr" in the cylinder that the ball slides in and once in a while it would get stuck for a short amount of time. He is a machinest so he was able to repair it easily. This happened around 100K.

Eric
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Old July 3rd, 2007, 11:59 AM
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Sounds silly, but also try just changing the oil filter. Backcheck valve may be no good, and you may be draining the oil out of the cooler and inlet tubes.

I have a similar thing going on lately, except mine is fine when starting cold but I need to rev the engine when I start it hot or I get no pressure.
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