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Fault P0126 Engine temp insuficiant / Bad Thermostats



Posts: 2008
Location: canastota ny
The thermostat pictured below was removed from a 2003 Chevy 6.5 litre with 12,000 miles on it. As you can see in the picture the rubber coating has come off and lodged itself in the thermostat holding it open. This causes the engine to warm up much slower than normal and set fault code P0126 in the P.C.M. (Engine Temp insuficiant for normal operation). Several of our 6.5l engines have had this problem all of which were fixed by replacing the thermostats. Some of the thermostats look like this one and some look normal but the engine will only warm to 160 deg. or so instead of the normal 185 deg.
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gpjeep1974 User avatar

i was talking with kenny @ monroe school transportation today, he has 8 gm 6.5 liters that aren't putting out any heat. is there anything else that might be causing this problem?


Posts: 2008
Location: canastota ny
The best thing to do is check the temperature of the heater cores. If the temp is lower than the engine coolant temp then it could be a restriction or air in the heater core. Some have a vacuum controled valve on the right side of the engine that can malfunction or the vacuum pump could be bad. If the engine is not getting up to temp then its the thermostats.


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