'94 LT1 oil pressure

[BMFer1]

Have a '94 Z-28 w/LT1 (p engine) with a couple oil pressure questions. The previous (original)owner said it has been the same for as long as he can remember.

When the car is cold, and until fully warmed up, gauge reads around 35ish to 50 psi depending on rpm. Once the car is fully warm, oil pressure at idle in gear is barely above the red (about 8-10 psi, I guess) and goes as high as 25-30 psi with engine speed. I just changed the oil with Mobil1 10W-30 and the idle pressure increased, but just barely (maybe 1-2 psi.)

Is this normal? I have a new Autometer gauge I considered hooking up in place of the oil pressure sending unit to see if the readings are inaccurate, but I have not tried this yet. Just wondering if there are any known issues you guys can inform me of.

The car has 95,000 miles, no oil leaks (any more )

[CamarosRsweet94]

I guess I would try changing hte oil pressure sensor to make sure it isn't that. However, replacing it with the autometer gauge might work too. Personally I think that the stock gauge is just displaying it low. Since you said that it increases when you increase engine speed, I just think that the gauge is displaying it too low, but you never really want to guess when it comes to oil pressure.

[malletslinger]

Before you change the sensor or anything, try running some oil system cleaner with the oil...
Go buy some GUNK oil system cleaner(pepboys), 5qts of new oil, and a new filter...drain a qrt of oil from engine, then add the GUNK system cleaner to the oil(the cleaner comes in qts), run for 5 mins, then drain the oil immediately(if you remove the oil fillter cap, it will drain faster) and just leave it for like an hour(so you can be shure it drains all the old oil and the cleaner out because it will thin the new oil if there is much left in there) the oil just seems to be dripping out, jack up the front of your car a bit so what ever is left comes out faster...Then replace the plug, change the filter, and refill the oil system.
If you are worried about the trace amounts of cleaner thinning out the new oil, then you can add a little oil stablizer(dont need more than a 1/4 of the bottle) before you pour in the new oil and take your car for a drive. This could fix the problem, if not then at least you know the oil system is clean

[chevy_chic20041]

had the exact same problem with my95 changed the switch oil pump and screen still didn't work now my other 95 runs about 20 to 40psi

[tntmik91RS]

I had a similar problem with my '91. Thankfully, it was the oil pressure switch. When I bought the car a few weeks ago, engine cold oil pressure was 45psi. Once it warmed up, it would be between 15-30psi at idle, and 30-45psi when the rpm's increased. Couple of days ago, my oil pressure was 0psi at idle when it was warm. When I increased the rpm's, the best I got was 15-20psi. After I let off of the accelerator, the gauge would instantly drop to about 10psi, bounce around in the "red" section, and then go back to 0psi. I immediatley thought it was the oil pump. I mean, it is a '91 with 125k. So, I started the trouble shooting process: easiest/cheapest first (I would have added "obvious" first, but it wasn't that obvious with alot of different components). I had the oil changed and put a bottle of Slick 50 in it. No fix. So, I changed the oil pressure switch next and that fixed the problem. The gauge is reading just as I previously described. Next on my list was either the instrument panel or the oil pump. I put oil pump at the end of my list because it's alot harder to change than the instrument panel. And considering my factory tach is about 1000rpm's off (reading higher than actual), I just thought the panel was going bad, bit by bit. Not only that, but oil pumps either work, or they don't. There's no "going bad" with an oil pump. I'd still do what Malletslinger suggests. He's an awesome poster with alot of knowledge. I'm just passing on what fixed my car. I've checked, and an oil pressure switch for your car at Advance Auto Parts will run you between $25 - $36, depending on which one you need.

[malletslinger]

Originally Posted by tntmik91RS

I'd still do what Malletslinger suggests. He's an awesome poster with alot of knowledge.

You're too kind...when I take over the world, your life shall be spared

My suggestion had two reasons behind it. One is it fixed the pressure problem in my 89...the other is that you dont know how well the engine was maintained and there could be stuff in there gumming up the system...The problem may be the pressure sensor, but Id recommend doing this too.

[BMFer1]

Thanks for the replies, folks. The engine has been maintained very well. All records came with the car. The oil/filter has been changed religiously every 3k at a Chevy Dealer. A few oil leaks were repaired too, which makes me wonder if the old man that owned it checked the oil. I had to replace several seals (crank, distributot shaft, & water pump shaft) as well as the water pump & distributor cap/rotor/plugs/wires. I just hope the engine hasn't been damaged from running low on oil (if it has even been run low.) I'm not particularly fond of engine flushes, but I may try that if all else fails. What I was talking about trying in my original post was to temporarily connect the Autometer pressure gauge in place of the factory sending unit to see if it may just be a sending unit or gauge issue. That's why I asked if there were any such common issues. Again, thanks for the help/suggestions, and any further help is greatly appreciated.

[tntmik91RS]

In order to install the Autometer gauge, you're still going to have to remove the factory oil pressure switch, so it would just as easy to replace it. And, if it doesn't fix your problem, you can either return the part, or leave it in; you've just eliminated one of the potential problems. The problem very well could be the instrument cluster. I know they have a tendancy to go bad. Either way...six of one, half a dozed of the other.