lost oil pressure

[jahearne]

Bad luck with 250 oil pumps! Changed the oil last night, this morning ran fine, stopped at the store, oil light came on. Removed the oil pressure switch, not a drop came out when restarted the engine. Lifters clackin' and got it towed home.

This is the second pump on a new engine. While tuning up the motor, the oil light would come on from time to time, so I replaced the first oil pump. Worked fine after that. Replaced with a new stock pump from A&A auto parts.

With the second oil pump, it became a quart low once and the oil light came on and stayed on even after I topped it off. Removed the oil pressure switch, spun the motor, oil squirted out, replaced the oil switch, no problems till now. I've probably put over a thousand miles on since. Little over two thousand miles since I got it running.

I'm going to tear it apart this afternoon to find out what's wrong. Anybody else have bad run with oil pumps?

 

[250mav]

could this be a case of cheap china parts?

i lost a fuel pump over the summer that was only on the car for 6 months

 

[fordconvert]

So the pressure was good to start with and then fell off? What did the pump(s) look like when you took them out? Unless the rotor and housing is trashed about the only other thing in the pump that can cause it to loose pressure is the relief valve. Melling is somewhat known for minor issues with those hanging up on some of the less popular models.

 

[The Plankster Prankster]

man, get a real gauge on that thing!! the idiot light never told me enough to diagnose anything!

 

[jahearne]

Good point, I do need a gauge! All I did was remove the distributor and prime the pump with an old distributor shaft, heard some gurgling after that it didn't take long to get oil to the rockers. Put it back together and it seems fine... seems fine won't know for sure until I get a gauge.

Like it was some kind of air pocket... so what now, everytime I change the oil I have to prime the pump ??? When I replaced the oil pump, I didn't check the distance from the pickup to the pan, but I was careful to prevent any internal leaks; the pickup looked good, etc. The second oil pump is still in there. The original pump looked fine, no damage to the rotors, no scoring, looked brand new. How can I tell if it's a bad relief valve? watch the oil pressure with a gauge, right?

 

[fordconvert]

The valve is just a spring loaded piston. I have not had one of the ford ones that far apart but in other pumps what happens is the piston gets stuck on a burr or other chunk of crap and does not return to its normal closed position. A quick spike in pressure (like a cold start with a quick rev) makes it extend and stick and then who knows if it will unstick itself or just bypass all your oil.

 

[jahearne]

That makes sense. Thanks!

 

[addo]

The stopper/piston is supposed to "float" in its bore. I mean, at road revs, it should be slightly off the dead stop position, and oil passing past it via the entire periphery. If you pull the bypass assembly apart, clean the bore carefully and make sure both ends of the bypass stopper are gently rounded so it can't cock sideways and bind.

 

[rbohm]

8) i usually find lost oil pressure under the workbench in the farthest corner closest to the wall........................

oh wait, thats lost tools

i agree with addo. take the pump apart and clean the relief passage out and make sure the piston floats freely. check the tension on the spring to make sure it hasnt lost any. last check the piston for burrs that might prevent the piston from moving freely.

one more thing, replace the oil pressure switch as they tend to go bad more often on the six for some reason.

 

[BIGREDRASA]

Out of curiosity, what oil were you running. 0W-20? 15W-40? Regular, synthetic or synthetic blend?

 

[jahearne]

15-40W dino for diesel engines.

I'll give the relief passage a work over.

 

[BIGREDRASA]

Unless you have a diesel, I'd stick with a 10W-30 Motorcraft Synthetic blend. On a new engine with tight tolerances, a 40 weight could be a bit much on a cool morning.

 

[jahearne]

I only went with diesel engine oil for the additional zinc, zddp. I'll give Motorcaft Synthetic a try. It's been cold in SF, but not that cold.