PFF - Pennock's Fiero Forum, PDA Edition

Fiero 87 gt loosing oil pressure randomly (Page 1/2)

Rune82

JUN 14, 07:51 PM

So I have a 1987 Fiero GT 2.8l V6

Every startup its makes 50 - 60 PSI of oil pressure

Once warm it makes around 40 - 45

Once i am driving it after about 10 mins the oil pressure will drop slowly over time

and completely randomly when coming to a stop it will either make 20 PSI or 5 psi or less

Once it starts having the 5 psi issue if you rev it up it will make 40 easily then slowly drop off

It runs perfect no knocking no ticking no weird noises

And i have confirmed with a mechanical gauge

82-T/A [At Work]

JUN 14, 08:02 PM

Your car can't really run at 5-PSI... if you were really getting 5-psi, you'd have significant lifter clatter, even when sitting at idle.

What you're experiencing, in my opinion, is likely a failing oil pressure sending unit.

Here's a diagram from the Fiero Store:

The oil pressure sending unit is the one circled in blue. You will want to replace this... but MAKE SURE you buy the correct one. There are a lot of oil pressure sending units for sale on places like Rock Auto, etc... and they are these tiny little "sensors." Those are not sending units, those are "oil pressure switches," often mislabeled as a sending unit. The sending unit is the big one that you have, and that allows you to power an oil pressure gauge. The small ones are binary... pressure YES or NO.

Be careful when you unscrew that oil pressure sending unit, it's mounted to a steel block which is connected to a tube which is notionally mounted to the side of the engine. What you'll want to do is get a crescent wrench where the open end will fit perfectly over the block that the oil sending unit is screwed into... use that to hold the block STILL... and then use another crescent wrench (13mm I think... I can't remember) to unscrew the sending unit.

Note, even though the sending unit is super big and looks like you can put a big wrench on the plastic part, you'll really just destroy it... so unscrew it from the metal part at the tip where it screws in.

This is what you need to buy: https://www.rockauto.com/en...info.php?pk=11762449

Patrick

JUN 14, 08:13 PM

quote

Originally posted by Rune82:

And i have confirmed with a mechanical gauge

How many miles on the engine, and what oil viscosity are you running? You should probably be using 10w-40 if you aren't already.

[This message has been edited by Patrick (edited 06-14-2025).]

Rune82

JUN 14, 08:20 PM

IV tested it with a mechanical gauge its jittery between 5 - 15 psi

and the sending unit is brand new aswell

Rune82

JUN 14, 08:21 PM

quote

Originally posted by Patrick:

How many miles on the engine, and what oil viscosity are you running? You should probably be using 10w-40 if you aren't already.

103k miles as of yesterday

and im using 5-30

thinking of switching to 10:40 to see if it helps

Patrick

JUN 14, 08:33 PM

With those miles, and summer temperatures, I suspect you'll see a healthy improvement in oil pressure with the higher viscosity oil.

Rune82

JUN 16, 03:26 AM

quote

Originally posted by Patrick:

With those miles, and summer temperatures, I suspect you'll see a healthy improvement in oil pressure with the higher viscosity oil.

I changed the oil ima go for a drive at some point tomorrow already had a noticeable effect cold its making over 70 psi now

Dennis LaGrua

JUN 16, 04:32 AM

Depending on how the engine was maintained and driven a 103K miles could be considered old and worn. Excessive wear might be helped By using a 1 grade less viscous oil. 10W30 might work well but it will only delay the inevitable engine rebuild or replacement. Any engine 40 years old is ancient and was just not designed to last forever. Don't mean to be harsh but that's the bottom line.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Spadesluck

JUN 16, 09:20 AM

If it where mine this is what I would do:

1. Check oil, make sure I got enough
2. Do an oil change, maybe go to a higher weight
3. Try a different oil sender
4. Try a different oil gauge

Dennis LaGrua

JUN 16, 10:40 AM

One possibility that hasn't been discussed is a possible defective oil pump