chris1

On my 1991 Automatic L98, the oil pressure gauge seems like it is possessed or something. I purchased the car a couple of months ago from the second owner, and it has 62,000 miles on it with most of the original parts on the car. I noticed the oil pressure sender unit was leaking so I replaced it with a new GM unit. The gauge will work properly for the first 5-10 minutes or so of driving until I guess the oil warms up. Then, when I initially step on the gas, the needle will flutter and move past the 80 psi line until either I let off the gas, or the car shifts into the next gear. When I'm stopped at a light or stop sign, the gauge will move back to around the center as normal. When I'm cruising at a steady speed, the needle will stay steady, and hover right near the 80 mark on the gauge. The gauge did this even before I replaced it with the new GM unit, as I thought this would have killed 2 birds with 1 stone so to speak, in effect stopping the oil leak, and correcting the fluttering action of the oil pressure needle. The car runs perfectly, doesn't use any oil, and doesn't have any knocking or sounds on start-up, so I'm guessing there are no internal engine issues, or problems with the oil pump itself. I am using an AC Delco PF1218 oil filter. There was an AC Delco PF454 on it when I bought it, so the filter change didn't seem to make a difference. I am using Mobil 1 10W-30 Fully Synthetic Oil, and added a quart of Slick 50 for added protection as well. Do you guys think I could have gotten a bad sending unit from GM? The sending unit was only $18.34 plus tax from the dealer, so it's no big deal to maybe get another one to see if it cures the problem. Any thoughts or suggestions? It's not a big deal, however the other gauges and everything else on the car works properly, and being a Corvette guy, I want everything to work properly on the car if at all possible, especially if it can be easily fixed in a minute or so by replacing something as simple as the sending unit......

Thanks, Chris.

adi4

I would check that the plug on the sender is fully home and also make sure that there is no insulation broken away an the wire and it is touching ground ,

It sort of sounds like an engine movement issue and a plug not fully home, I would check this first but yes it could be a bad sender.

If you bring the engine revs up when you are stationary and in park ( if you have an auto ) or neutral ( manual ) does it do the same thing or is it OK ....

19corvette91

i dont trust the factory gauges......period..............for these 3 reasons combined
1)flaky sending units
2)old wiring that can have higher resistance
3)sticky/ flaky gauges themselves

my 2 cents/ just venting

chris1

The needle will flutter when the transmission is in park, as long as the oil is up to operating temperature; the engine seems rock solid, and doesn't move on the mounts at all, so I'm leaning towards it not being an engine movement issue, especially since the needle doesn't flutter during the first few minutes of driving. It appears the connector is seated correctly on the sending unit itself. I'm at a loss for what is causing the needle to flutter, other than another bad sending unit........

11yellowgscpe

Hopefully you are aware that the L-98 has 2 oil switches. The top one is for the idiot light on the dash, the out switch is the one that controls the gauge. Make sure you replace the correct one. I have replaced both and the gauge no longer bounces.

chris1

I was wondering in the back of my mind if the other switch may be the cause. The top was the real easy to get out with the proper oil pressure switch socket. That is the one that is kind of facing you as you are leaning over the car from the driver's side looking down at the distributor. I have a factory service manual, and just wanted to verify that the one you are referring to is the switch that is actually laying horizontally, connected to the fitting just below it. Did you have to remove the whole distributor to get it out, or just the distributor cap by itself to give you enough room to get in there????????

trevkris2

chris1...
Question for you. I've got an 89 that I need to have the oil changed on, and I was considering switching to Mobil 1 synthetic, and wanted to find out if that's what you did on yours. Did your car have the conventional oil in it when you got it? Did you notice any differences switching to the synthetic? Are there any drawbacks of switching whne a motor has 82K on it? Your thread brought up a very good question, and I sure hope you can help. Cheers!

trevkris2

Anyone?????

RIISITAS

I've switched to Mobil 1 from conventional oil on two cars with high mileage that I purchased used. (78K on one and 104K on the other.) I switched to Mobil 1 on these cars, first because its superior to conventional oil and second because at the time I was living in the in the North where we had extremely cold temperatures. Synthetic motor oil makes starting an engine in sub zero temps much easier as well as giving you nearly instant oil presuure. I had no problems with the switch at all and drove both of these cars for quite a few years.

91vettemo

I have a 91 Auto L98 also. My oil pressure gauge does something similar. When you first start it up, it has good pressure. You drive all you want and it stays high, then if you stop it goes way down. Not sure why it does that but its not leaking any oil, doesn't seem to be a problem, just bugs me.

Grace91

The sender that lays horizontally is the one for the gauge. You should have no problems getting it out after you remove the distributor cap.

We had a thread going on this same subject last night.

http://forums.corvetteforum.com/show...38&forum_id=48