Here are some possible causes of low compression in just one cylinder:
* Burnt or damaged valve: This is a common culprit. A valve could be warped, sticking open or closed, or even broken. This can often be repaired by replacing the valve(s) and potentially grinding the valve seats.
* Broken or damaged piston rings: These rings seal the combustion chamber. If they're broken or worn, compression escapes. Repair involves removing the head and replacing the piston rings. This is more involved than a valve job but still cheaper than a new engine.
* Hole in the piston: Less common but possible. This would require piston replacement.
* Head gasket leak: While a head gasket leak usually affects multiple cylinders, it's possible a localized leak between that cylinder and the cooling system or externally could cause significant compression loss in just that one cylinder.
* Incorrect valve timing: Although less likely, a timing chain or belt issue could lead to improper valve timing and compression loss in a single cylinder.
What you should do:
1. Get a second opinion: A different mechanic might offer a more detailed diagnosis. It's important to find a mechanic specializing in older vehicles, as their expertise will be invaluable in troubleshooting this issue.
2. Compression test specifics: Ask for the *exact* compression readings for each cylinder. This allows for comparison and a more accurate diagnosis. A single low reading could point to issues related to that single cylinder, while a general low reading across multiple cylinders may indicate other problems.
3. Leakdown test: This test can pinpoint the source of the compression leak (valves, rings, head gasket). This test is highly recommended before considering a new engine.
4. Consider the cost: Get quotes for the repairs mentioned above (valve job, piston ring replacement, etc.) Compare these costs to the price of a new engine or a used engine replacement.
In short, while a new engine is *a* solution, it's not necessarily the *only* solution, and it's almost certainly not the most economical. A thorough diagnosis is essential before making any major decisions about your Tahoe.
