2007 Hummer H3

The 3.7L LLR Atlas inline-5 cylinder engine consumes oil at an excessive rate, with some owners reporting 1 quart consumed every 1,000-1,500 miles. The piston rings do not seal properly, allowing oil to pass into the combustion chambers. Symptoms include low oil level warnings between changes, blue exhaust smoke during acceleration, and fouled spark plugs. Running the engine low on oil accelerates bearing and cylinder wear.

Monitor oil level frequently and top off between changes. GM considers up to 1 quart per 2,000 miles within normal parameters. For consumption exceeding that threshold, piston ring replacement is the definitive fix but requires engine removal and partial disassembly. Some owners switch to a heavier-weight oil (5W-40 or 10W-30) to reduce consumption. Using a quality full synthetic oil may also help.

The H3 is prone to various electrical malfunctions caused by corroded ground connections, particularly the engine-to-body ground straps that are exposed to road spray and off-road conditions. Symptoms include intermittent starting issues, flickering lights, gauge malfunctions, power window failures, and random warning lights. The ground strap behind the engine and under the cab are common corrosion points.

Inspect, clean, and re-torque all ground connections, particularly the engine-to-body ground strap located behind the engine, the ground strap under the driver's side of the cab, and the battery ground cable. Apply dielectric grease or anti-corrosion compound after cleaning. Add supplemental ground straps if the factory grounds are severely corroded.

The H3's cooling system is marginal for the weight and aerodynamics of the vehicle, particularly when towing, climbing hills, or driving in hot climates. The radiator develops internal blockages and external fin corrosion. The water pump can leak from the weep hole, and the thermostat may stick closed. The engine temperature gauge climbs rapidly in demanding driving conditions.

Replace the radiator if it is internally clogged or externally corroded. Replace the water pump if leaking. Install a new thermostat rated at 195 degrees F. Flush the cooling system with a quality coolant flush product and refill with the correct Dex-Cool mixture. Some owners install a larger aftermarket radiator or auxiliary transmission cooler for towing applications.

The transfer case develops fluid leaks from the output seals and encoder motor gasket, and the front differential pinion seal leaks. Low fluid levels from undetected leaks cause internal wear, grinding noises, and eventual component failure. The transfer case encoder motor can also fail, preventing the 4WD system from engaging or disengaging properly and displaying a 'Service 4WD' message.

Replace leaking seals in the transfer case and front differential. Replace the transfer case encoder motor if the 4WD system is malfunctioning. Change the transfer case and differential fluids at the recommended interval (or more frequently if the vehicle is used off-road). Reference GM TSB 07-04-18-001 for transfer case diagnosis on the GMT355 platform.

The exhaust manifold bolts on the 3.7L inline-5 break due to thermal expansion and contraction cycles, creating exhaust leaks. The leak causes a ticking noise on cold starts, exhaust fumes near the engine bay, and potential entry of exhaust gases into the cabin through the HVAC system. The broken bolts are difficult to extract from the aluminum cylinder head without damaging the threads.

Extract the broken exhaust manifold bolts, which may require drilling and using an easy-out extractor. If the bolt hole threads in the cylinder head are damaged, they must be repaired with a thread insert (Heli-Coil or Time-Sert). Replace the exhaust manifold gasket and install new bolts. Some owners use stainless steel replacement bolts for improved durability.

General Motors LLC (GM) is recalling certain model year 2006-2010 Hummer H3 vehicles manufactured February 5, 2005, to May 24, 2010, and 2009-2010 Hummer H3T vehicles manufactured May 21, 2008, to May 24, 2010. In the affected vehicles, the connector module that controls the blower motor speed for the heating, ventilation and air conditioning system may overheat.

If the blower motor connector module overheats, it can increase the risk of a fire.

GM will notify owners, and dealers will replace part of the blower motor connector and harness, free of charge. The recall began February 26, 2016. Owners may contact Hummer customer service at 1-800-732-5493. GM's number for this recall is 15042.

GM IS RECALLING CERTAIN MODEL YEAR 2006 THROUGH 2010 HUMMER H3 VEHICLES. SOME OF THESE VEHICLES HAVE A CONDITION IN WHICH THE INTEGRAL CLIP-TABS ON THE LOUVER ON THE HOOD MAY FRACTURE, CAUSING THE HOOD LOUVER RATTLE AGAINST THE HOOD AND BECOME LOOSE. IF THIS INDICATOR IS UNNOTICED, ADDITIONAL CLIPS COULD FRACTURE AND THE HOOD LOUVER COULD DETACH FROM THE VEHICLE.

IF THE VEHICLE IS BEING DRIVING WHEN THIS OCCURS, IT COULD STRIKE A FOLLOWING VEHICLE AND CAUSE INJURY AND/OR PROPERTY DAMAGE.

DEALERS WILL APPLY AN ADHESIVE TO THE HOOD LOUVER TO SECURE IT TO THE HOOD. THIS SERVICE WILL BE PERFORMED FREE OF CHARGE. THE SAFETY RECALL BEGAN ON APRIL 12, 2010. OWNERS MAY CONTACT HUMMER AT 800-732-5493 OR AT THE OWNER CENTER AT WWW.GMOWNERCENTER.COM.