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Re: engine compression Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 25 Jul 2002 08:52:15
In Reply to: engine compression, Alex Reid, Thu, 25 Jul 2002 06:56:41 Members do not see ads below this line. - Help Keep This Site Online - Signup |
As Gary says, the variation between the numbers is an issue. You really do want to see no more than about 10-15 psi.
Compression ratio varies from year to year, and model to model. But in general, the turbo engine has about a 9:1 compression ratio. That means an 'ideal' compression of about 133 psi, give or take. This car has one cylinder about 25 psi low (110), and another about 20 psi high (165). The low compression could be bad rings, valve seals, or burnt valves. The high compression cylinder could be carbon buildup or stuck valves/lifter problems.
That high a compression in a turbo engine is a problem, as that cylinder will be more prone to knock well before the others.
This sounds like a problem engine, and the fixes are expensive. Unless the car is a screaming deal, and you have access to another engine, walk away.
An additional note - I assume this was a 'dry' test - the mechanic just sticks the tester on the engine as is. There is another test, called a 'wet test'. After doing a dry test, the mechanic drops a teaspoon or three of engine oil into the cylinder, turns the engine over a couple of times, and re-runs the test. The oil will act as temporarily seal between the rings and cylinder walls. If the compression increases with a wet test, then the problem probably is with the piston rings/cylinder walls. If not, then it's probably valves.
Good luck!
posted by 140.157.4...
, Thu, 25 Jul 2002 08:52:15 <-- Viewing This Message
, Thu, 25 Jul 2002 10:26:14, Thu, 25 Jul 2002 22:08:58, Thu, 25 Jul 2002 15:36:04
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