Oil pressure

I finally got everything buttoned up on the re-engining of my WRX, but came up with a question about starting it up for the first time.

The WRX only has an idiot light for oil pressure. I've cranked the motor with the fuel pump relay disconnected to see if it will build pressure and turn out the light. It has not.

The geeks over on NASIOC say that it's unlikely to build pressure with just the starter. I guess I can believe that.

Do I start it for real and hope I get pressure? How bad is it if I run for a few seconds without oil pressure? What would GRM do?

I have been able to get oil pressure with the starter on my Stags V8 with only the starter motor. I also installed a gauge instead of just an idiot light ( replaced the non functional clock) so I could make sure I was building pressure.

The majority of my experience is with Chevy V-8s, but I've messed around with other cars as well. I would think if you can't get oil pressure off of the starter, there's a problem. Sometimes it just takes a while. Pulling the spark plugs out will help it spin easier. Me personally, I wouldn't think of putting spark to an engine I haven't seen oil pressure on yet.

Yeah, never seen an engine that wont build oil pressure with the starter

install a mechanical gauge, if you don't get oil pressure don't even try to fire it.

Did you prime the pump? The starter is more than capable of building pressure in the system.

If it's a new/ rebuilt engine definitely prime before spinning it if you can. Not sure what drives the oil pump on a WRX or how ez it would be but on SBCs I always use an old distributor w/ the top guts removed and the driven gear ground down, just slot it into the oil pump drive and spin w/ a 1/2" drill to prime. Just built one the other day for the 4.3, it was ez.

If its new rebuild and the pump was not primed before installing you'll have a hard time to get it primed up. Scubies drive off the crank if i recall correctly so no way to prime now but cranking. Pulling the spark plugs would let it spin over faster but thats a BIG pain on a flat 4... Did you fill the oil filter before installing it right? You could pull out the sender light (top left front of motor under alt..i think) and plumb up a can of oil and force it in to the galleys while turning the motor over that would back prime and and get the bearing lubed while cranking. Parts stores used to sell cans to do that but not seen in years.

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Many engines will not build oil pressure on the starter motor. If it were mine, I'd fire it up and give it a few seconds to see if it finally builds pressure.

The 'crank driven' oil pumps can take some time to build pressure since they are above the level of oil in the crankcase, unlike the olde tyme pumps which hung down inside the oil pan and were thus immersed in oil, or at least were a lot closer. (For future reference, pack the gears with Vaseline during assembly and it will pick up pressure a lot quicker.) In the meantime, pull the plugs and remove the oil pressure switch (this allows air to escape quickly) then spin it until oil comes out of the switch hole. Then reinstall the plugs and switch and fire it up.

If you coated the bearings with engine oil, that has pretty much all run off by now so I'd not risk running it with no oil pressure. IMHO that's why Subaru had a fair amount of trouble with main and rod bearing noise back in the '90's. If you used that red sticky assembly lube it should still be there and might protect the bearings.

There are some excellent engine assembly lubricant products on the market that adhere to the bearing and cylinder walls very well to protect them until pressure is established. Like Curm. said, by packing the pump with Vasaline it has much better ability to pick up the oil under initial start up. I used it for years.

foxtrapper wrote: Many engines will not build oil pressure on the starter motor. If it were mine, I'd fire it up and give it a few seconds to see if it finally builds pressure.

This. Mine will only build about 1-2psi. I usually check to see if it's working by un-hooking the oil feed line from the turbo while priming and keep cycling the starter until i see oil come out of it. If it comes out, the pump works.

Just how WELL it works remains to be seen until the car actually runs.

OK, I took the spark plugs out and am spinning the engine with the starter. I tried it both with and without the pressure switch installed. Few blasts of 5-20 seconds. Still no luck.

Am I FUBAR, or just a nancy boy who needs to keep trying? I mean, I've tried 2-3 blasts of 10-20 seconds.

My Subaru takes a few seconds of RUNNING to build pressure. Cranking won't do it.

peter wrote: OK, I took the spark plugs out and am spinning the engine with the starter. I tried it both with and without the pressure switch installed. Few blasts of 5-20 seconds. Still no luck. Am I FUBAR, or just a nancy boy who needs to keep trying? I mean, I've tried 2-3 blasts of 10-20 seconds.

Unhook a small oil feed line somewhere near the top of the system. Make sure it's got oil coming out of it. If so, you're good.

What I do when installing a new oil pump is pack some grease in it. Very heavy oil will work as well. You need something that will seal the gears to the housing so that a vaccumn will occur and suck the oil from the sump.

Since the engine is spinning over freely (spark plugs out) the starter's not working near as hard as it normally would. Man up and spin that bad boy! Long shot: pull the PCV valve out of the valve cover, make sure all the other openings to the crankcase are closed off, then put a little air pressure to the PCV hole while a bud spins the engine. Do this politely so you don't blow a valve cover gasket or etc out!

It's ALIVE!

no amount of plug-less spinning got the light to go out. Even with the oil pressure switch removed, etc.

Within 1 second of cranking with fuel and spark, light went out. Motor runs!

WOOOHOOO! (my first motor removal/rebuild/transplant/etc)

Thanks all

Congrats!

good call on trying it with spark and fuel.. it could have ended badly, but didn't

In reply to peter:

Is your motor still running happily? I am in the same situation with my Saabaru... No amount of plug-less cranking is priming it. Ive tried pouring oil into the oil pressure switch port to try and back fill behind pump. No luck yet. I think I am at the scary cross roads of try it and see what happens. Wish I would have read/thought about packing pump with grease first.