Low oil pressure (and dummy light) only at low idle...

[Falcon4]

Me again. Aren't you glad to see me? :salute:
(edit: Also figured this was a better place for the topic, since Maintenance and Tech seem to have a rather, eh, blurred line...)

I REALLY don't want to get into this system. All the other things I've dealt with have been easy to get to... hell, even the head gasket was easy compared to the oil system. But here it is, it seems to be an "unimportant" problem, but a worrying one none the less. Unimportant, because it only revealed itself after replacing the gauge that would tell me (meaning it's probably been like this for a long-ass time).

Oil pressure. When I first got my Fiero, I had a problem with HIGH oil pressure, so I thought. I don't know if it'd always done it, but the oil pressure gauge would start tweaking out at low RPMs, seemingly shorting out and pegging the gauge at totally random times, like a vibration was causing it. It looked like a VU meter on a rock song or something. So I replaced the sensor. BAM, problem solved. No more whacked-out readings... and to be more precise, it actually showed me a more logical reading as well.

When the car's cold, even after it comes down to 800rpm when the O2 sensor warms up, the oil pressure gauge shows slightly above the red mark. If I tap the gas and get the RPM up to 1000 or so, the pressure shoots up to the normal range and stays there no matter where I rev from that point. Kinda like a logarithmic graph. But after driving the car for a while, like on the freeway going to work, when I stop at a light and it's idling in Drive (haet automatic), the oil pressure enters the red area and the Oil light flickers on and off - sometimes staying on.

There's plenty of oil, up to the top of the add/full gauge, and it was just changed with good 10W/30 oil (I can't remember what brand, but it was a name-brand, not cheap shit). The guy at AutoZone recommended I add some of this "oil stabilizer" stuff as well, so I did, but after finding I already had it at "full", I didn't add the entire bottle. I didn't think it was that great an idea either...

Now, this doesn't really worry me at the moment because obviously a gauge isn't going to cause a problem, meaning it's probably been like that for a while and hasn't, well... hasn't caused any problems yet (the engine still runs great). But I'd love to know if it is really a problem, from a professional's point of view.

And, uh... is there anything I can do about it but just let it happen?

[Fastback86]

Not to be a downer, but when my old 2.8 was doing that, it was on its way out. But mine also had low compression on one cylinder and lots of blow-by. Anyway, you need to figure out how serious the problem is, and the best way to do it is with a mechanical gauge, since as you know, the one on the dash is notoriously inaccurate. If your oil pressure really is getting low, you need to figure out why. If your motor has one foot in the grave like mine did, it may not really matter. If its healthy otherwise, you may want to check out the oil pump and see if its worn out.

Wish I could be of more help, but like I said, my motor was dying, so I kicked it to the curb and never looked back.

[The Dark Side of Will]

The 3.1 in my 6000 was doing that. It had ~220K on the clock at the time. I replaced the stock pump with the high volume pump, but put the stock regulator spring into the HV pump before installing it... problem solved. You also get to fix any leaks at the pan gasket, R&R the engine mount, etc, so you can double up the effectiveness of your effort.

[p8ntman442]

get a mechan ical gauge, and install it where the oil pressure sender screws into the T fitting. See what your dealing with, a gauge problem or a oil pump problem. If its an oil pump problem you have several options. One is to add sawdust to the oil and buy a big FOR SALE sign. Anothe is to replace the pump, and the last is to swap in a good motor.

I know your broke like the rest of us, maybee more than most. So the best advice I can give you is to swap in a new oil pump, stock replacement will work fine or the HV with stock spring as will said. Its a decent amount of work for the novice, but nothing you cant handle. You will need to block the front wheels, jack the ass end way up, and put jack stands on in front of the rear tires. Crawl under the car, remove the motor mount, jack the engine up, and block it up. Pull the oil pan, remember the oil pickup will catch the baffle in the pan, so it wont fall down, you will have to move it sideways to get it off. Replace the pump, and oil pan gasket, and oil.

[Pyrthian]

1st Q - when the pressure is reading way low - does it tick? if no - the pressure is NOT to low (yet)

you can drop the oil pan, and replace the main & rods bearings. this will often help.

a verification of pressure, with a mechanical guage is a good idea - but - what you are experiencing is pretty common - and I'd believe you got low pressure. but, thruthfully - you can go down to 10psi at idle. not, the greatest, and the OIL light does irratate.

anyways - fresh bearings & oil pump is the "right" answer

[The Dark Side of Will]

The drop in oil pressure over engine life is caused by various clearances critical to maintaining oil pressure opening as the engine wears. The stock oil pump can no longer move enough oil to maintain pressure in the bearings and the oil pressure light comes on.

Solutions:
-Reduce bearing clearances through overhaul (hard)
-Install oil pump that flows enough oil to maintain pressure with new bearing clearances (easy)

Both are equally effective.

[Pyrthian]

.....
Solutions:
-Reduce bearing clearances through overhaul (hard)
-Install oil pump that flows enough oil to maintain pressure with new bearing clearances (easy)

Both are equally effective.

and - both are equally easy - you drop the oil pan. from there, you can easily change the rod bearings. and, if your feeling good about it sofar - you can change the main bearings - little tougher to roll 'em in & out - but can be done.

the only bearings that are tough is the cam bearings. and, unforturnatly - they are first in line for oiling. so, they do have the most impact on pressure.

[The Dark Side of Will]

Dude, the oil pump's a LOT easier than the bearings.

If nothing else, the pump requires one bolt vs. 12 for the rods and another 12 for the mains; then there's the effort to R&R the bearings (x10); time spent plastigauging to verify clearance, etc.

[Pyrthian]

Dude, the oil pump's a LOT easier than the bearings.

If nothing else, the pump requires one bolt vs. 12 for the rods and another 12 for the mains; then there's the effort to R&R the bearings (x10); time spent plastigauging to verify clearance, etc.

yes, true. its just since you've already done the work for the oil pan, no reason not to. plastiguaging is basicly just doing that bearing twice. but, yes - the bearings are more work that the oil pump - but - both are simple compared to getting to that point.

[The Dark Side of Will]

I disagree... I don't think getting the pan off in a Fiero is that big a deal. You should try it in an A-body (Pontiac 6000).

Jack the car up.
Remove exhaust (bolts to Y-pipe may be a chore).
Jack engine up and support crank pulley.
Remove engine mount and bracket.
Remove pan.

Rodney Dickman makes a tool that looks like it will make the exhaust springs a relative breeze.

[Xanth]

Bit of a side note, my 2.8 Firebird had a similar issue where the gauge would drop down too low at an idle.

Problem on that was actually my timing, it was way retarded which seemed to lower the idle enough that the pressure dropped though the RPM's still looked okay on the enormous Tach that thing has.

It probably had other issues as well, on a good motor I imagine the oil pressure should not have dropped that low regardless but correcting the timing did get it back to a reasonable operating range using 5w30 oil. This motor is at 131k or so, my Fiero at 100k still has excellent pressure using 5w30.

Definitely do the pressure checks they've mentioned with the mechanical gauge, especially being up there in miles. I would also just double check that your Idle is actually where its supposed to be. On my Bird I couldn't even tell the difference on the Tach after correcting the issue, but it definitely idled a bit higher.

[befarrer]

Replacing the rod bearings on an engine will only take up 1/2 of your clearances, the crank wears too. I dont know about the 2.8, but you have to remove the oil pump on my Quad 4 to get to the crank.

[The Dark Side of Will]

The oil pump bolts to the #4 main cap in a 2.8.

[Pyrthian]

Replacing the rod bearings on an engine will only take up 1/2 of your clearances, the crank wears too. I dont know about the 2.8, but you have to remove the oil pump on my Quad 4 to get to the crank.

and, again - the cam gets oiled first - so - if your loss is there - the rods & mains are moot. but - you'll never know. at least I have yet to find a way to easily verify the condition of cam bearings.
first cam, then mains, then rods. rods are LAST on the oiling path - well, other than cyl walls, which are purely oiled by splash.

and, another thing I learned yesterday....there is a oil seal in the #4 main cap....never noticed it before....and, I've been thru this motor several time....lol. you actually supposed to put sealant on this cap & a fresh o-ring. you can in fact lose oil pressure here.

[p8ntman442]

and, again - the cam gets oiled first -.

Is this correct, I thought oil went from pump to crank, rods, up to camshaft, out to lifters and up through the pushrods back into the drain at the valve covers.

correct me if I'm wrong please.

[Kohburn]

lots of things can cause lot oil pressure at idle since thats when its pumping the least.

high flow pump and replace the bearings while you have the pan off will probably keep it alive for a while longer

[Series8217]

and, again - the cam gets oiled first -.

Is this correct, I thought oil went from pump to crank, rods, up to camshaft, out to lifters and up through the pushrods back into the drain at the valve covers.

correct me if I'm wrong please.

What motor are we talking about here?

IIRC the cam gets oiled first on a 2.8. Then mains and lifters. I need to look at the oil diagram to verify though.

On a 3.4 the cam and mains get oiled at the same time. From cam it goes to lifters and up through the pushrods. From mains it goes to rods.

[befarrer]

I dont know how a 2.8 works for oiling. But I thought most engines had the crank oiled first, and worked its way up the block, ending in the valve covers.

[Falcon4]

Whee.... lots and lots of posts since I closed the tab and forgot about my question. I've since almost forgotten about the light. It still comes on but I don't put nearly as much an "OMFG!" emphasis on it as I did when I first saw it come on (neutral and kill the engine on the freeway offramp, then coast as far as possible with hazard lights on, push to a safe place, then sit and think "WTF?!"). That was fun.

Seriously though, when I did the head gaskets umpteen months ago, the block looked really clean and new. The story goes that the last owner put a new short block in, and I don't doubt it considering the shitty job they did (with a folded-over head gasket and a second, disconnected leftover temp gauge on the wall-side head - I replaced with a plug). I don't hear any difference in noise, thank god, when the pressure's low, so although that's not necessarily a good indicator, it could be considered a "good thing".

I guess I could go with the mechanical gauge, to test. But like I said, the new gauge is what revealed the problem - read: new gauge - so we're not dealing with old crappy parts here. If the pressure really is for reals, I guess I may be in for some work. I haven't the slightest idea how to work with motor mounts and whatnot, so I might be in for some reading and asking. But like I said, the oil pan needs replacement anyway to be rid of the strange threads that throw off oil-change places... so who knows. Might be the all-around good thing I needed.

I just shudder at the thought, considering I need my car for work :scratch:

[Xanth]

Where exactly can you get a New fiero oil pressure gauge?

Are you referring to the Sending unit on the engine or the Gauge in the car?

New non-GM sending units are notorious for low readings.