2000 Jeep Grand Cherokee Repair Question
When I first start my vehicle and it's cold it knocks when given gas. Why is that?
Do you mean it rattles for a couple of seconds right after it's started, or will it do it after the engine has been running for 15 or 20 seconds? If it does not knock after it has been running 15 seconds or longer, simply try a different brand of oil filter. Some have a check valve to prevent oil from running out of the filter while the engine is off. At start-up, it takes a little time to refill the filter with oil, and until that happens, there will be low oil pressure to the engine bearings. They have up to .006" of clearance that lets the parts hit each other and make a loud knocking sound. Once pressurized oil gets there, it takes up that clearance and quiets the noise.
Some engines have that oil check valve built into the engine and another one isn't needed in the filter. When it's not needed in the filter, some manufacturers don't put it in. Later, they may find that filter will also work on a different engine, and they box and label it for that application. It will filter the oil just fine but without that valve, that knocking could occur.
My first experience with this was on a '90s Dodge Shadow 4 cylinder. The girl's husband had been using Fram oil filters on that car for years with no problem, but the noise showed up right after the previous oil and filter change. Switching to a Chrysler filter solved the knocking noise at start-up.
If the knocking occurs long after the engine has been running, start by measuring the oil pressure with a mechanical gauge to see if it's low. If it is not low, check for a loose vibration damper or some other mechanical problem.
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