Nissan Repair: Dead Cylinder on 06 xterra, blown head gasket, piston rings

Question
QUESTION: I have an 2006 xterra off road.  Purchased with 60k mi now has 74k.  Truck has burnt oil since i bought it. Have already replaced a clutch then my engine light started flashing truck was missing.  Took it to my local mechanic (trustworthy) and they tested the compression in one of the cylinders and said it is essentially dead.  Is this a problem that you have seen before.  Am I looking at replacing an engine?  If so what could that potentially cost.  If it is a valve or ring issue what could be an estimate for cost of that sort of repair.
Should i get rid of this truck once its repaired?

ANSWER: Hi Andrew -

There a a couple things that could cause a cylinder to loose compression. Did you mechanic say what the compression is? Is it low, or zero?

Most common is is a blown head gasket, or burned valve. The cost could be about $2,000 +, depending on whether you want good, better, or best.

The only thing that would make it costly is if your piston rings are shot. If there is some compression then a simple test of injecting some engine oil into the cylinder, crank the engine and take a compression test. If the compression improves greatly, then the rings need replacing.


Hope this helps -
aloha
calvin

---------- FOLLOW-UP ----------

QUESTION: thanks so much for the prompt response.  Compression was low but not zero.  They did a wet test and were still unable to get the compression up.  Ive been lead to believe that this short of issue could damage a catalytic converter.  What so these run?

Answer
Hi Andrew -

Excessive conditions may impact the CAT, depending on what is causing the low compression, but the CAT is usually able to handle minute discrepancies in exhaust compositions.

So it looks like you have either a burned valve, or a small break in your head gasket. Have you checked if there is water in your oil? Run the car until operating temp, and then pull your dipstick out and spill some oil onto the exhaust manifold. If it sizzles, then you have water in your oil, and it is the head gasket as opposed to the burned valve.

Hope this helps -
aloha
calvin