* Blown Head Gasket: This is a very common culprit. A failing head gasket allows coolant to leak into the cylinders or vice versa, leading to a loss of compression. You might also see white smoke from the exhaust, overheating, or milky oil.
* Cracked Cylinder Head: A crack in the cylinder head allows compression to escape. This often accompanies a blown head gasket but can occur independently. You might also see coolant leaks.
* Warped Cylinder Head: Overheating can warp the cylinder head, preventing a proper seal with the head gasket. This results in a loss of compression.
* Burned Valves: Burned or damaged valves prevent the cylinder from sealing properly, resulting in a loss of compression. This often occurs due to overheating or lack of lubrication.
* Broken Piston Ring(s): Piston rings seal the combustion chamber. If they're broken or severely worn, compression escapes. This often leads to oil consumption and blue exhaust smoke.
* Hole in Piston: While less common, a hole in a piston will certainly result in zero compression in that cylinder.
* Valve Seat Problem: The valve seats wear down over time. If they're badly worn or damaged, the valves won't seal properly.
Diagnosing the Problem:
To find the exact cause, a mechanic would likely perform these tests:
* Compression Test: This is the first step. It measures the compression pressure in each cylinder. Low or zero compression pinpoints the problem cylinder(s).
* Leak-Down Test: This test identifies *where* the compression is leaking from (past the rings, valves, or head gasket).
* Visual Inspection: A mechanic will inspect the engine visually for obvious signs of damage or leaks.
In short: Don't try to start the engine repeatedly if it's not firing. This could cause further damage. Getting it towed to a mechanic for diagnosis is crucial to identify the root cause of the lack of compression and avoid costly repairs later.
