i have an 85 gt, bone stock 2.8, and the last couple days the oil pressure gauge is acting a bit wonky. on hot idle it bounces around and is erratic. under any sort of power or on a cold idle it reads about 70 (which i know is probably not correct but that has been the norm since ive had it). i am hoping it is just the sender... any thoughts? thanks.
From what I've read on the forum, the bouncing oil pressure gauge is common in our cars. The oil pressure sender is the culprit, but I've never been bothered enough to install a new one.
Oil pressure will read higher under a cold idle because the oil is still thick and not warm. Oil works it's best when it reaches an operating temperature that allows it to thin out, flow, and lubricate everything fully. It should also increase under load, because of obvious reasons.
The sender can be tested, but your better option is to obtain a mechanical oil pressure gauge and hook it up to where the sender would go. This would allow you to get an accurate reading on oil pressure. From there you would likely be able to deduct whether or not the sender needs replacement.
Mechanical oil pressure gauges can be had pretty cheap, and you'll likely be able to rent one (like through AutoZone's tool rental program) or maybe know a mechanic friend that has one.
The 85 type oil pressure sender - the big one - tends to fail in a manner that it gets so high and then any oil pressure above that just pegs the meter full scale.
This is normal!!! Don't waste your money on a new sender. My 86 V6 SE and our present 88 GT V6 both exhibit this same behavior. THe problem is likely some weirdness inside the resistance element in the sender. At some point I want to run experiments and see what is really happening. I changed the sender on my 86 and the problem was back in short order. It *did* go away for a while though.
Ray and Kevin is right don't waste your money. It seems after I change the oil it goes away for a while. Also when I took out the sender and cleaned the hole with a needle it seemed to work better. What the hell give it a try.
[This message has been edited by fierobug (edited 03-25-2013).]
It's common in the Fiero but not normal, or intended to be that way. It's either a design flaw, or poor aftermarket quality in the sending unit. It should work as smooth as a properly functioning fuel gauge with the pressure fluctuation like in pretty much every other car with a gauge instead of a light from that era. All of mine did across 3 F-body cars and my other Fieros.
I'm currently experiencing the same problem that didn't start out that way with a BWD sensor which is said to be a poor performer. Some members switched to the 88 model sensor preferably in a GM part to fix it. A frequent erratic needle swing from 10 psi to 40 at steady state is annoying and inaccurate.
Joseph is correct. It is common but not *normal* (but then neither am I). As I said, I want to find out exactly what is happening when I get one of those round tuits. I think Joseph is right that there is something hinky about these senders, but my original GM and a replacement GM back in the 80's did not solve the problem. When I find out I'll post to the group.
Just started encountering this issue. Mine is nice and stable at a certain pressure however if bounces (fluctuates) plus and minus 5 or so. I switched to a brand new AC Delco unit and not I have some serious swings...plus or minus 40 or more. It seems to be stable at speed until I let off the accelerator. That is when it bounces severely.
