1996 GMC Jimmy


Old 10-04-03, 12:26 PM
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Angry 1996 GMC Jimmy


This truck is beginning to tick me off!

It is making a knocking sound that comes and goes. I've tried a better oil and still. It is not a really bad sound - like rods on the verge or anything. Its just annoying. Especially after having the transmission rebuilt just a year ago. It has 228,000 miles on it. The knocking starts at cold start and when the car has been driven and parked(say at the grocery store) then started again. It quiets down after about 10 minuets of drivng.

The owner's manual(of course) says not to add any additives and just to take it to the dealer. I would like to add something like an engine treatment or something. Any Ideas people? Does it sound serious?
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Old 10-04-03, 12:45 PM
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Since you say the noise comes and goes, I wouldn't be surprised if your hearing lifter noise. An old trick you might try is adding a quart of Auto Transmission Fluid to your oil, it might clean them out. Chances are with that many miles they are just plain tired.
Old 10-04-03, 03:27 PM
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10 minutes is a long time to quiet down if it really is an oil problem. Despite that, I will go with my first thought. Change the oil filter, install a manufacture filter like ac/delco or other proven brand.

The anti-drain back valve built into oil filters is known to cause engine noises after startup due to oil starvation because the oil drained out of the filter when the engine was shut off. This is not suppose to happen. It can take up to two minutes for the oil pump to fill all the oil channels in the engine as a result of the oil filter being drained of oil. The anti-drain back design of modern oil filters has been around for many years and is generally not a problem for most cars, but it rears it's ulgy head from time to time. This start-up oil starvation is a 'known' problem related to oil filters and some truck engines.

The only two oil filters that I can think of that cause this problem are Fram and Penzoil filters, but I'm sure there are several others. The anti-drain valve simply does not retain the oil after the engine is shut off, as it should. In other words, the oil filter must be full of oil at all times, engine running and engine off. I believe Wix and ac/delco and several others are recommended for their superior design or construction and this is your best bet to approach this problem. I'm not knocking Fram for the average car but if you are having startup oil starvation noises, that is the first thing to look for. Also be sure you are running the correct SAE weight oil for your vehicle for the anti-drain back valve to be effective.

Last edited by Lugnut; 10-04-03 at 04:35 PM.
Old 10-05-03, 08:48 AM
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You're up there in mileage so the thing doesn't owe you a nickel....

Additives do nothing. That is why GM says so in the owner's manual. Regular maintenance does. 10W30 and an AC Delco oil filter is where I would start.

If you suspect it's a real problem, then have it investigated. Have the oil pressure checked with a mechanical gauge. It is probably out of spec a bit at that mileage.

My vote: Drive it till it grenades and then worry about a rebuild or replacing the truck. What grade of oil are you using and how often is it changed?

I never throw high dollar additives, oil or parts at my vehicle. They just drain your wallet. Regular maintenance pays off in the long haul.
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