I have a 1999 hummer H1 and have a rear head cooling unit installed for 3 or 4 months. I have recently been noticing a bouncing in my water temperature gauge reading. It happens about every other time i drive it. It almost mimicks my RPM gauge. It instantly shoots up when i press on the gas and instantly back down when i let off the gas. It also bounces upward over each bump in the road. There is plenty of coolant in resevoir. Has anyone ever had this happen or heard of this. Any easy fixes for this?

 

you have air trapped in the cooling system. you will have to bleed out the system to get it to stop doing that. those head cooling kits do more damage then good on the 6.5 turbo diesel engines. the original design of the engine was to have rear head block off plate to force the coolant back to the front of the engine to cool off the upper cylinders and blocks. when you install the head cooling kit it takes that pressure away so you are only cooling the bottom of the engine. i was going to do this years ago on our race Hummer but AM Engineering, who build the motors and designed and built our race motor told me never to do this. i have replaced a lot of head gaskets and replaced heads that had the cooling kits on them. customers said that the vehicle never got over 220 degrees and still caused damage.

 

Figured it out while driving for 3 hours to the lake. smelled antifreeze about 2 hours of driving. turns out i had a leak at the top of the radiator dripping onto the fan. I lost a quart of antifreeze. limped to autozone and bought a few gallons of premixed antifreeze and added Bars Leak. Did the trick and was able to make it to the lake house and back to Richmond VA today with no temperature spikes. Going to flush system and replace radiator with aluminum set up. I guess the pinhole was letting air into the system and i was getting the funky temp readings. I never drove it far enough to see the leak.

 

Have a new predator aluminum radiator and it works great. no funky temperature gauge. In fact i can drive at 70mph in 100degree weather and never cross the 200 degree line. advise all who are willing to shell out the $1400 to do so. great investment. Still believe my head cooling unit is also a great investment as well.

 

One of the oldest and most respected Hummer mechanics in the country just got through saying that the head cooling unit was not a good idea and is not recommended by AM General. If you are happy with it so be it but I would recommend that most owners heed the advice of the experts.