CJSingbeil

A big hello to everyone here, I am new to the Chevy forum. I myself am a member of the Jeep CJ forum, and with their help I have rebuilt a '79 CJ7. I turned to this forum because my dad owns a '95 Silverado 1500, and we need some help with it. As the title suggests, the vehicle is aging. It was purchased from a used car dealership some time ago, and currently has over 320,000 kms on it. For the minimal amount of trouble we have had with it, that is incredible.

Now to get right to the point, this truck has been hauling things around for years, in work truck role. Can't remember the last time it was in for a service, but I took it upon myself to perform some maintenance. So I changed plugs, distributor rotor, PCV valve, air filter, and fuel filter. It was long overdue.

Anyway, over the past few weeks my dad has been noticing a drop in oil pressure. The gauge normally sits at 275 or so, but it has been dropping to less than that. After the little tune up I preformed, during a test run, the pressure dropped down to scarcely above the red line indicator. Oil level was good, and there was no abnormal sound or leaks on the ground. So is the pump starting to go after all these Kms? I realize how worn the engine must be, but I don't want the thing to be run into the ground due to a failing oil pump.

Sorry for the long post, I'm trying to make sure I haven't left anything out. I am not used to the TBI the truck has, or the electronic gauges, or anything about it, really. My CJ has a Carter carb, and mechanical gauges. Any feedback is greatly appreciated.

maxxman04

when was last oil change? what weight/viscosity oil was used? it is possible pump is going out. not sure if you've heard of or can get it, but i would use Lucas Oil Stabilizer. see if that helps.

CJSingbeil

The last oil change was castrol 10w30, and it was less than 1000kms ago. I have used Lucasoil before, and we are running about a liter of the stuff in with the regular oil. I'd like to take this opportunity to ask if anyone has heard of using a heavier diesel oil in these engines. In my gasoline AMC 258 I am running Rotella 15w40 diesel oil, and it seems to work great. High pressure, no ticking or noises, and the pressure stays up even after the engine is warm. Would it be advisable to use such an oil in the 350? I know people who swear by rotella, and run it in trucks to lawnmowers.

maxxman04

15w40 is fine to run in your motor.

kevinkpk

I take it the values are in Kpa, thats about 40 psig. As your engine wears the clearances are going to get bigger, so, oil pressure will also drop.

CJSingbeil

I realize that, but the pressure just started dropping over the past few weeks. The gauge is in Kpa. So normally at an idle, the gauge would read half, which is 275, and would increase with the rpms. Over the past few weeks, the gauge has worked itself down to a normal pressure of 1/4 of the gauge (I'm not familiar with the numbers). Now on the last drive, the regular pressure was at about 1/8 of the gauge, hovering just above the red line, and it did not increase with rpms.

kevinkpk

I'd suggest if you can verify the pressure first. You could go with a higher viscosity oil, however what was stated 10-40 should be good.

maxxman04

you might try flushing motor. drain about a quart of oil. then add a quart of transmission fluid. let engine run for bout ten minutes and drain. trans fluid will help to clean out oil passages. if that dont work then its time for new pump.

kevinkpk

You could use a quart of diesle or tranny fluid. Those oil pumps are gear pumps, could be wear, I'd suspect if pump, it is crap plugging the screen. Either way you will have to drop the pan. If you replace the pump, you will need to prime the new one. Might add it could be sludge, either way if you have to drop the pan, I'd suggest replace the pump.

skeeter5

CJ,

I think that you may want to connect a pressure gauge to the engine
and see what the pressure is. You may have other problems, other than
the oil pump or the lower end having excess wear. The only real test that I remember is removing the pan and put pressure into the engine gallery and see where the most oil is coming from. Cam bearings, mains, or rod bearings.

Not trying to bring you more gloom.

Just check the actually pressure, before you attack.

My .02.