oil pump priming weirdness

[mnviper]

I have a 2005 SRT/10 which I’ve been trying to get running for longer than I can remember now. Last fall I installed a newly-built engine (pistons, rods, bearings, main caps etc.). I was prepared for a bit of work to prime the oil pump, but it turned into a real ordeal. I tried numerous methods and succeeded finally with a vacuum line from another car attached to the oil cooler input line while I cranked the engine (with the plugs out).
When it finally primed and I reassembled the lines I watched the gauge come up well over 50 psi while cranking. I assumed the battle was over.
I started the car and ran it for a short time but then left it alone for about a month while I waited on some other parts.
However, when I went back to the car after a month, cranking it showed it was back to 0 psi with the pump showing no signs of priming. It was getting pretty cold in the garage so I threw in the towel for the year.

Today I decided to start the battle again. I hooked up my vacuum setup to the cooler input line again and watched it start to pull a steady stream of oil. However after about ½ a quart (I assume the amount held in the oil filter) the line went to mostly air with dribs and drabs of oil. Oddly, cranking it in this state caused to pump to prime again. So I’m back to healthy gauge pressure but I’m worried about the fact that it lost its prime.

I’m thinking that the fact that I can draw more air than oil out of the cooler input line might be a clue as to why it was difficult to prime and why it lost its prime. Any ideas what might cause this? Shouldn't the path from the cooler line to the pickup tube be air-tight? BTW, the engine has plenty of oil.

[Tiago]

maybe a broken O-ring in the oil pump pick up tube.

[Greg Good]

It's not a good idea to crank the engine a lot on the starter. The way I prime a complete engine is to apply 3-4 psi to the crankcase, then spin it with the starter and no spark plugs. It'll prime within about 4 seconds. If that's not possible, it's better IMO to just start it up. On the starter, the engine is not turning enough rpm for the oil pump to create much of a pressure drop.

I would call the engine builder to see what he recommends.

[Dan Cragin]

Greg made a good comment about putting pressure into the engine crankcase to build oil pressure. Another way that we often use, is to remove the oil pressure sending unit and use a pressurized oil tank to prime the engine. We use shop air pressure to do this. We do this on new motors or engines that have just been half re-assembled.

Odds are, on a engine that has sat for a long time, if you make sure the oil level is up and you are running thin oil, 0-10w40, just cold start it and let it idle, it will build oil pressure within a few seconds.

[mnviper]

maybe a broken O-ring in the oil pump pick up tube.

This has crossed my mind and I was wondering if anyone else would suggest it. If the engine does lose its prime again I'll take the pan off and have a look at it.

Greg, I did try the pressure approach but have had better luck with the vacuum on the cooler line. So I think I have a handle on how to prime it now I just didn't think I would need to be doing it multiple times.

Dan, You mentioned thin oil. One of the things I'm starting to regret is that I have Joe Gibbs 20w50 break-in oil in it, which probably isn't helping matters.

My main concern is that the fact I can suck air from the cooler line (which leads directly to the filter then the pump) is indicative of some sort of sealing problem. Or perhaps the oil pump chamber really isn't meant to be that air tight.

[SA Heat]

I bought a factory GM crate engine years ago that wouldn't develop oil pressure....ended up finding the pickup and bolts that were supposed to hold it on in the bottom of the oil pan. To this day, I still haven't figured out how that could have happened. It must have been a Friday build.