The H3's 3.7L engine has an issue with worn, leaky valve seats that cause the engine to misfire. Usually the only way to stop the problem is to replace the cylinder head.
The 3.7L engine in the 2006-2008 H3 is a leaky mess. Well, at least its valves are. Somewhere around 87,750 miles1 the valves and valve seats in this engine are susceptible to wear and tear.
The engine valves open and close to bring air into the cylinders and force exhaust out. If the valves aren’t tightly sealed while closed, the cylinder loses compression, the engine misfires, and you start saying words that your children probably shouldn’t hear.
Even before misfiring, a leaky valve can decrease the engine’s power and hurt its fuel efficiency.
Valve Stem and Seat Wear
Valve stem wear is very common in high mileage engines, I just wouldn’t classify 88,000 miles as high. And while pushing the engine too hard can degrade the valves quicker, the most common reason for early valve wear is sloppy machining tolerances during manufacturing.
There is very little room for error when it comes to a properly closed valve. In fact, valve seat wear in the H3 can often be misdiagnosed as ScannerDanner shows on YouTube.
A quick visual inspection of the 5-cylinder engine usually won’t show any problems, it’s only once you remove the valves and carefully inspect the seats that you can see the wear.
Fixing the Problem
Sometimes you can get away with only replacing the valves in the cylinder head, but if the wear is significant enough you might have to replace the entire cylinder head.
On average, owners pay about $2,5801 once their vehicle falls out of warranty.