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Bob
Bob, Auto Tech
Category: Chevy
Satisfied Customers: 4087
Experience:  Plus 40 years GM, over 30 certified with Chevrolet, ASE certified Master Tech. (Expired, Retired)
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2000 chevy: I have replaced two O2 senors and catliytic converter

Resolved Question:

I have a 2000 chevy Prism and it is using oil but there is no evidence of oil anywhere on the engine. The car has 94k miles. I have replaced two O2 senors and catliytic converter.
Submitted: 6 years ago.
Category: Chevy
Expert:  Bob replied 6 years ago.
Hello, if the car is using oil and there are no leaks, then it has to be burning it in the combustion chambers. This is normally a sign of broken or worn parts like piston rings. The best way to get an idea of the problem in your case would be to do a wet and dry compression test and then maybe follow that up with a cylinder leak down test. If you check the cylinder compression in the cylinders and write it down and then go back and squirt some light weight oil into the cylinders and check it again, if you see a sizable increase in the readings, that is a pretty good sign that the piston rings are worn. As, when you ad the oil to the cylinders if the rings are worn, the oil will tend to make a seal between the rings and the cylinder wall and that will raise the compression because there will be much less leakage of the compression past the rings. Doing a leak down test will help to confirm the problem. You remove the spark plugs and with the aid of a measuring device available at most parts stores, you bring the cylinders up to top dead center one at a time and then inject compressed air into the cylinders and measure the amount of leakage of the air pressure being induced into the cylinders. Then you listen to see where the air is escaping from. If you hear air in the crankcase or out of the oil cap hole, the problem is with the rings or pistons, if air escapes out the exhaust you know there is a problem with the exhaust valves, if it comes out through the intake or carb or throttle body, you know the intake valves are leaking and if you get bubbles in the radiator or air out of the cooling system that points to a problem with the head gasket sealing or a crack in a cylinder or cylinder head. Hope this info gives you a little more in site into testing to find out where your oil is going thanks.
Customer: replied 6 years ago.
My question to you the expert where is the sign that oil is burning. Would you get at buff of smoke out the exhaust pipe? Don't you get that from burnt valve stems and worn piston rings.Iam consuming a quart of oil a week if I drive the car 5 or 6 hundred miles.

Tell me if this makes sense to you. If the oil ports in the head and block are clogged would this cause oil to burn in the exhaust pipes and catalytic converter so no smoke is seen. If the valve cover is removed I would find oil pooling in that area. This is just a question.
Expert:  Bob replied 6 years ago.
Hello, You have some good thoughts as to the oil pooling in the valve cover, but if it did so, the only way for it to go from the top of the cylinder head into the cylinders, would be past the valve seals and valves. The only thing that connects the inside of the combustion chamber to the top of the heads is the valve stems where they go through the head and then the valves open into the combustion chambers. Yes, if you pulled the valve cover, you should see oil pooled on the top of the head if that was the case. You should also see an awful big build up of sludge. And chances are pretty good that if the oil was pooling that badly, it would find a way to leak out around the valve cover gasket. Normally, if the valve seals or the valve guides are bad, the oil will tend to pool up some what around the valve stem and flow through the seals and past the guides into the cylinders in a rather large amount at a time and in this instance you should (normally) see a puff of smoke out of the tail pipe when you first start the motor after it has been turned off for an extended period of time, like 5 or 6 hours or over night. But if the piston rings are bad, there is a good chance that the oil will go past the rings at a steady enough rate that it will burn pretty completely before it would have a chance to make smoke out of the tail pipe. Because of the extreme heat built up in the catalytic converter. As I said before, if it is using that much oil you only have a couple of places it can go. Out the tail pipe as burnt oil or on the ground as an external leak. The only other option that comes to mind would be if it had an oil cooler mounted inside the radiator, similar to the transmission oil cooler. If that was the case and the cooler was leaking, it would have oil in the cooling system. But, I can't recall that car ever using a remote oil cooler. I have seen many motors that used oil, that did not smoke. But again, the simple tests I gave you should confirm if the reason is motor wear or not. Thanks
Bob, Auto Tech
Category: Chevy
Satisfied Customers: 4087
Experience: Plus 40 years GM, over 30 certified with Chevrolet, ASE certified Master Tech. (Expired, Retired)
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