Leaky Valve Seats Are Causing H3 Engines to Misfire

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.

  1. Based on 2006 H3 owner data from CarComplaints.com  2

Where This Problem is Likely to Occur

Model Generation Years PainRank
H3 1st Gen 2006–2010 11.56

What Owners Are Saying

“This is the third time in 140,000 miles that the valves/head have gone bad. The first time was at about 47,000 miles, the second time was about 99,000 miles, and now again at 140,000 miles. The first thing I noticed was it was running rough/missing when I started it the other morning.The next day the check engine light was on. My husband used a reader and the code is P0300/multiple misfires. The first 2 repairs the car was under a factory warranty and then an extended warranty, but now it is out of warranty.”

2006 H3 Owner in California

OK, Now What?

Maybe you've experienced this problem. Maybe you're concerned you will soon. Whatever the reason, you can help make sure it gets the attention it deserves.

  1. File Your Complaint

    CarComplaints.com is a free site dedicated to uncovering problem trends and informing owners about potential issues with their cars. Major class action law firms use this data when researching cases.

    Add a Complaint

  2. Notify CAS

    The Center for Auto Safety (CAS) is a pro-consumer organization that researches auto safety issues & often compels the US government to do the right thing through lobbying & lawsuits.

    Notify the CAS

  3. Report a Safety Concern

    The National Highway Traffic Safety Administration (NHTSA) is the US agency with the authority to conduct vehicle defect investigations & force recalls. Their focus is on safety-related issues.

    Report to NHTSA

  4. Contact Hummer

    Hummer Support

    P.O. BOX 33177 Detroit MI 48232-5177 USA

    • 866-486-6376
    • @GM

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