Oil pressure at idle...

Well, I'm getting nervous.

So, I've rebuilt the engine in the Celica twice 'cause of a stupid mistake the first time. But I think I did everything right the second time. Tonight the oil pressure light came on at idle. It's pretty consistent too. I have a gauge on it- it's always been lower at idle. It's hard to say accurately because the gauge isn't marked for that kind of precision down low, but it's somewhere around 10 psi at idle. It's up to 50 or so cruising down the highway. Gets up to 75 or so at high revs.

The oil pump that came in the engine kit did kinda seem crap. Maybe I should change it out. It's only got about 5,000 miles on it. Engine runs great. No knocking or anything. No indication of trouble. I changed the oil and filter a couple of weeks ago. Mobil 1 5W 30.

Man, I really don't want to have to pull that engine out again. Any thoughts?

I have a 1985 Celica GT with the 22RE that I've been DD'ing for a few months. The engine in it is pretty tired, and the oil pressure sits just above the lowest mark on the OEM gauge at idle. I've never had the oil light come on though. I usually run 10W30 in it.

Which engine does that thing have in it?

For the "1984-85 Toyota 5M-GE"
From http://www.rebuiltautoengines.com/toyota-celica-articles.html
"The diameter of the oil jet in the camshaft was increased from .048 to .056. This change occurred in production beginning in May, 1985, with engine #5M-3675931 (see Figure 1). Toyota allows the replacement of camshafts in engines built prior to May, 1985 with the new camshaft without changing the oil pump and oil pan. The oil pressure switch should also be changed to the late model switch. The original camshaft #13501-43010 has been replaced by #13502-43030. The correct oil pressure switch for use with the late model camshaft is #83530-14050."

I was just about to mumble something about wondering whether you had any specs for your engine and stumbled into the above, which in turn made me wonder whether you could have something going on like that, where 10psi at idle is fine, but your sender's expecting 12 so you get a light... The engine's out of another vehicle, no?

It's the 22RE. It is out of an '85 Celica, but the car is an '84. They actually changed the 22RE quite a bit in '85, so could be. It's also a little odd because I have the light and no factory gauge. It's an ST and you don't often see them.

I have an Autometer gauge. It has a line with "0" next to it that I assume is zero. It goes below that line with no power, but with power and the engine off, it's right on that line. Next marked line is 25 psi. At idle it sits right on the line between those two, so 12.5 psi? Dunno, really.

That doesn't seem ridiculously low to me. I'll have to see if I can find specs for the two engines. If you rev it at all it jumps up quickly. It gets to 25 before 1,500 RPM.

I've found several posts on truck fourms that say the factory service manual gives a minimum oil pressure at idle of 4.3 psi. Maybe everything is okay. I replaced the sender for the light when I rebuilt the engine. It's a cheap RockAuto part. I guess I trust the Autometer gauge more than the light. It needs to go off though. Can't drive it like that. Gives me the willies.

I know the feeling. I blew up two rebuilds before I realized the oil pressure check valve/ball was missing from the block. Before the 3rd rebuild was fired off I wired up VDO pressure and temp gauges to be sure.

My idle pressure was like 10-14 psi. Seemed low and I couldn't find a documented idle pressure spec. It does hit the 70psi at 3000RPM that was listed though.

Of course my idiot light never went off even when there was a pressure problem

Verify with a new sender? I imagine they are cheap enough to swap out just for confirmation.

In reply to fast_eddie_72:

It might be worth it to get your hands on a calibrated test gauge just to be sure your cockpit gauge is accurate at that low of a pressure.

Yeah, I'm going to order another sender for the light. They're really cheap. I did check- Rock Auto show the same part number for '84 and '85. I've kept a pretty close eye on the oil pressure after going through one rebuild and I know it's not any different than it has been, at least on the gauge. Even by the light, it's sometimes so close the light can't quite decided if it's on or off. I'm sure those things aren't the most highly calibrated things in the world. I'll get another one and see what it thinks.

For reference, this is the gauge I have.

You can see the line between zero and 25. It sits right on that at idle.

Is this the number you're seeing cold or warmed up? At what RPM does it idle? Have you checked it against a different gauge?

-Warm

-About 850 RPM? Maybe 900. Factory tach. It's not accurate.

-Nope, not yet. Hasn't been a problem until now.

I'd keep an eye on the gauge, and try a conventional oil at the next oil change.

Strange as it sounds, I've seen different brands ( not weight) cause large changes in oil pressure at idle. I had a 4.3 in a boat that had close to 30psi at idle when running Amalie 10-30, and when I tried Quaker state I had approx 10psi at idle. Changed the oil back Amalie and the idle pressure returned.

It could have been a filter issue, I change the filter when going back to the Amalie, but since the idle oil pressure was back to normal I didn't investigate further and just stuck with Amalie and Carquest (Wix) oil filters.

Any possibility that a gasket is missing/leaking between the pump and the block?

you might try an idiot light sender from the 85...

Here is some info from the Toyota parts catalog....

83530 SWITCH ASSY, OIL PRESSURE (FOR ENGINE)

83530-14010 (08/1984 - 01/1985) 83530-14030 (02/1985 - 06/1985)

the 14010 was used in 1984, so you might look for a 14030

In reply to oldeskewltoy:

That's interesting. I appreciate you checking that. Did you notice, by any chance, if that was for the gauge or the light? My ST doesn't have a factory gauge, just the light. Most of them have the gauge.

But very interesting to hear it's a different part number. Something changed. And Rock Auto does have the same part for '84 and '85. Hard to say what I actually have in the car.

I did just go out and check it now that it's cold. It's over 25 psi cold. Obviously no light.

Ah, googled it and that IS for the light. THANK YOU!

There's one with the right part number for '85 on ebay. Buying it now.

10 psi per 1,000 rpm is an old rule of thumb, I think you're fine.

Electric oil pressure gauges are notoriously flaky down low. The only way to be sure is to nuke it from orbit.

Sorry, I mean the only way to be sure is to get a mechanical gauge.

12.5psi @ idle for a 22re is fine.

Honestly i'd be a little more worried that you're seeing 75psi on high revs.

Can you find what the recommended pressure at idle is in a factory service manual? I know modern engines only specify 10 psi because that is all that is needed at low load conditions

If your oil pressure is in spec at the rated rpm then idle pressure will be OK. Since the loads at idle are low, 10 PSI is sufficient. I never saw a service manual that gave idle pressure.

Well, we had snow. But I dug the car out today and took it for a spin. The light started coming on at higher and higher psi. Now it's on all the time. A lot easier to ignore it when it is on and I can see 50 psi on the gauge.

I did order that new sender for the light, so hopefully that will take care of everything. In the mean time, it'll be sitting for a while. We're flying out of town Sunday. Sure the part will be here when I get back.