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Matt, Engineer
Category: Cadillac
Satisfied Customers: 20397
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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I have been told that the pistons are bad and need replaced.

Customer Question

Mike,I have been told that the pistons are bad and need replaced. The car is using oil, Most of the time the car runs smooth. Sometimes it sputters, especially if I accelerate going up a hill. If I downshift from Drive to 4th, runs smoother during that time. The engine light comes on for a few days. Then I might start the car and the light stays off, and could be off for a couple of days, then comes back on. Does this sound like the problem?. If so approximate cost to repair?.
JA: Has your vehicled stalled? Has anyone run a diagnostic test to pull the trouble code?
Customer: No the car has never stalled. A GM dealer's service manager had the test done, but he did not give me the code. That service manger is no longer there.
JA: What is the model/year of your Cadillac?
Customer: 2005 CTS, 94000 on the car.
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I am not capable of doing the repairs myself I would have to rely on a dealership or an independent mechanic to fix.
JA: Anything else you think the mechanic should know?
Customer: No, I think that is all of the problems.
Submitted: 2 months ago.
Category: Cadillac
Expert:  Matt replied 2 months ago.


The first thing I'd check is the crankcase pressure relief valve (PCV) these are sprung loaded and are only meant to 'burp' excess pressure every now and then. The exiting gas is piped back to the inlet, however should the valve stick open then the engine tends to suck the air out of the crankcase all the time and this carries oil over with it.

If you remove the air intake pipe and look inside where the crankcase breather is plumbed in you may find evidence of oil.

If you do find oil replace the valve

. If this is all OK then its possible that the valve stem seals are past their best and are drip-feeding oil into the intake. These can be replaced without removing the head by a competent garage in half a day or so

an engine flush may also help if you've got a sticking oil scraper ring so its worth a go, as for the oil if you go up a grade / use slightly thicker oil then this is less readily drawn into gaps and less likely to be burnt off

Expert:  Matt replied 2 months ago.


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