Check gauges light - oil pressure..

[Gixster]

Over the last month or so, the check gauges light on my '94 LT1 M6 illuminates infrequently. I've already done a search and didn't find anything that covered exactly what I was looking for.

I read through the FSM and didn't find much mention other than the light will illuminate when the oil pressure, oil temperature, water temperature, or voltage hit the red range.

In my case, I think it's related to the oil pressure. When the car is cold, the oil pressure is fine, no light. When the car is warmed up and moving at speed, no light. The only instance the light comes on is when the car is at operating temperature and idling. Even then, it isn't solid. It will flicker as if it's right on the edge of the red range. When I look at the oil pressure gauge when this is happening, the gauge is *not* always in the hashed range. Does anybody know at what point the check gauges light is triggered in relation to the oil pressure? I was not able to locate that information in the FSM either. Also, I'm running 10W-40 Mobil 1.

How can I go about determining if the problem is actually low oil pressure, or if the sending unit is toast? I assume I need to get a mechanical gauge. It needs to be connected where the sending unit plugs in on the back of the block I'm assuming.

The car has 170k on it and runs great. No odd noises from the bottom end or the engine in general. It is a daily driver obviously. I don't beat up on it, but I do drive it like it's meant to be driven. I realize it might be bleeding off pressure through the bearings, but I'd like to figure out for sure if that's what is happening before I start entertaining an engine rebuild.

 

[JAKE]

I've read several posts on other Forums about the same condtition and even my son's 96 LT1 was doing the same thing. I strongly suspect bearing clearances have opened up a bit due to high mileage and normal wear.

Since you're not having any other problem (same with my son's), I simply moved from 5W30 to 10W40 Mobil 1.

That solved the low oil pressure reading and warning light at idle conditions and only minimally increased the pressure readings under other condtions.

Of course, there are a whole host of other things you could do like: installing a oil pressure gauge to verify the accuracy of the stock gauge; replace the oil pump/check for P/U screen blockage; change the oil pressure sender; have your PCM re-programmed to raise the idle speed to something like 900 RPM; pull the engine for a rebuild and probably others.

You can try raising the idle rpm with your throttle and see if the slightly higher rpm causes the oil pressure to increase and the warning light to stay off.

The only way I know of to determine if your bearing clearances have opened up is to mic the crank/rods/block.

Up your oil's viscosity and I'll bet your problem goes away but it's your call.

In your case, I'd move up to 15w40 or so. In the past I've mixed half 20w50 with half 10w40 to end up with 15w45.

I believe GM was able to get away with recommending 5w30 because the bearing clearances were set so tight in a factory fresh engine. Once those clearances open a tad due to normal wear, idle oil pressure falls off to a level that causes the low oil pressure light to illuminate at idle. However, at rpms higher than idle, the pressure would be okay. Vaguely, I recall reading somewhere that the light illuminates at 3/4 psi.

Jake

 

[Hib Halverson]

170,000 miles and you're on borrowed time, engine wise.

I'd check the oil pressure with a known-good gage. If it's low at idle...it's probably overhaul time. If it's reads ok, you may have a bad oil pressure sender(s)

After all those years of not giving you the light, the solution, as suggested elsewhere, is not to go to a higher weight oil. The solution is to fix the problem.