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Would a thermostat cause the heat to go from warm to cool and then warm? It doesn't over heat or anything the coolant is good but it does bubble. I just don't see any way of a head gasket. The temp gauges stays in the middle normal area never goes up past normal.

 
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Could.

Why would a full cooling system do this?Then explain the above question.

 
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Was thinking it wasn't opening correctly. I had it tested at a shop were they used a fluid to test the coolant and it was good. It don't get hot,smoke, or have water in the oil that's why I wasn't sure of head gasket. It does push it out into the overflow.

 
Rep Power: 518

Many blown head gaskets will pass all those common checks with flying colors.


A head gasket has maybe a dozen different jobs to do. Most people only look for about 3 or 4 of the more common failure areas.
They all do this as part of normal fluid expansion when heated, but the reservoir is supposed to go back to the original level when the engine cools down. And the radiator is supposed to stay completely full under all conditions.

If it fills the overflow reservoir while at the same time the radiator goes low.....


Read up on all the stuff about 7th gen head gasket issues.
6th gen uses the same gasket design.