Oil pressure drops while revving up motor (Page 1/2)
pontiacfierokid1985 OCT 08, 09:03 AM
2.8 with140,000 miles. Is it weird for the oil gauge to do this I’ll be driving around 5 miles to 40 mph keeping shifts under 3000 rpm but once in 4th around 40 mph 2500 rpm oil pressure will stay right at above the red should I be worried. If I’m doing highway driving 65-70 mph 3500-4000 rpm 4 speed Muncie it will be close to 40 psi what should I check into first
olejoedad OCT 08, 09:54 AM
Check oil level.
How old is oil?
Put a known good mechanical gage on it to check.
Blacktree OCT 08, 11:19 AM
Chances are the main & rod bearings are starting to get a little loose. You could try a slightly higher oil viscosity, and see if that helps. BTW, what oil viscosity are you using now?
Will OCT 08, 11:53 AM
You said Muncie, so I guess this is an '85 or '86 car.

The 2.8's received some oiling system improvements for '88; the older engines wear out faster.

You could have worn bearings or you could have a bad sending unit. I'd find a way to use a mechanical gauge (it is difficult) in order to check the sending unit. You could also just replace the sending unit and see if the problem goes away.

If you verify that the problem is real, you can install a high volume oil pump while keeping your original regulator spring.
pontiacfierokid1985 OCT 08, 02:59 PM
I just added a quart yesterday so it’s on the full mark. I changed the oil out when I first bought it 136,000 miles on odometer. I’m going to change the oil and filter this weekend. it’s been 3000 miles already so it’s needing to be done also going to add some Lucas oil stabilizer to it as well since that helps with thickening it. I’m looking into getting a 3800 sc series 3 with a 4t65 out of a 2004-2005 Gtp over the winter. I want to keep the 2.8 going as long as possible til the 3800 is done and ready to go on the 86 fiero cradle with the 4 speed that is in the car now love my stick shift cars will never go back to auto in my older cars.
olejoedad OCT 08, 03:57 PM
The Fiero owners manual calls out 8000 mile oil changes.
The additive packages in modern oils dont even kick in till 3000 miles.

In your case, if the oil is clean on the dipstick, change the filter and top of with Lucas.

You're wasting money and resources changing oil at 3000 miles unless the engine exhibits a lot of compression blow-by.
theogre OCT 08, 04:34 PM
Yup... Even in the '80's, 3000 mile oil change is a myth/scam push by Jiffy Lube and others.

Adding any aftermarket crap to engine oils makes a lot of issues like Two additive packs can fight each other or add too much zinc etc that can poison the cat etc over time.

Heavy oil just hinds a problem and often makes more problems like using 10w to 20w anything won't flow in winter in a lot of places. So if you have wear problem now you often only get worse or car won't start in cold weather because heavy oil is grease.

Dash Gauges often have problems. Yes, check w/ a real gauge on OP port. 6V w/ AC is very easy but w/o AC have to go under the car.
Drop outs at higher RPM can engine/trans mounts bad and pulling on wires etc. Check mounts and dog bone(s).

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Blacktree OCT 08, 04:43 PM
I agree with the above. The 3000 mile oil change interval is marketing hype. The owner's manual is a more reliable source of information.
82-T/A [At Work] OCT 09, 03:48 AM

quote
Originally posted by pontiacfierokid1985:

2.8 with140,000 miles. Is it weird for the oil gauge to do this I’ll be driving around 5 miles to 40 mph keeping shifts under 3000 rpm but once in 4th around 40 mph 2500 rpm oil pressure will stay right at above the red should I be worried. If I’m doing highway driving 65-70 mph 3500-4000 rpm 4 speed Muncie it will be close to 40 psi what should I check into first



Concurring with the other responses. Many years ago when my 87 was my daily driver, I had a similar issue. Turned out my oil pressure sending unit was going bad. It's located right off the front of the motor, which is facing the passenger side. It's that little cylindrical device that screws onto a tube that sits towards the front of the car off the engine. They're not expensive... but you can also test with a mechanical gauge.

If it's not that, 140k miles on an 80s car can be brutal if the oil hadn't been changed regularly. Not disagreeing with the guys above me, but our cars were generally run hard. Typically oil would get dirty and contaminated, and the engine would burn away some of the oil (blow-by) and be allowed to run low... further quickening the degrading of the oil that was left in there... so it was not uncommon for these motors to wear around that kind of mileage. With any car, good oil and checking the oil regularly would keep them running much longer.

If you are experiencing main bearing failure... (as in, the gauge is right), might be worthwhile to start succession planning. Either a new crate motor, or a bottom-end rebuild. I've seen people change out main bearings in a parking lot... don't recommend that, but it'll get the job done... hahah.

Another option is a windage tray and a new oil high-volume oil pump to make up for the loss of pressure from the enlarged clearances.

quote
Originally posted by Will:

The 2.8's received some oiling system improvements for '88; the older engines wear out faster.




Do you happen to know what these changes are? I've owned 9 Fieros, but not a one of them have been 88s. I know the oil pump is different, but curious if there's anything else specifically. I don't assume there's anything I can simply take from the 88 and install in my own 87 motor?


Thanks!
Dennis LaGrua OCT 10, 02:45 PM
On cars where there was low oil pressure, we found one where the oil pump was pumping lower pressure, another where the oil pressure sender was defective and one where the engine was just high mileage worn. Its most likely one of these issues.

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