Heater blows intermittently and temp gauge goes erratic?

This query was asked by my customer for his ford expedition vehicle.
In his case the thermostat was replaced,but still the same problem is getting noticed.


As per this details the possibilities that can cause such problem is as follows :-----
The problem  is very likely trapped air in the cooling system due to the fact the cooling system wasnt bled properly during the thermostat replacement and trapped air will cause the heater to be intermittent as well as the gage to read erratic. It will also cause the overheat code to set because it caused it to overheat. I would start with having the cooling system bled once again nd then be sure its top off to completely full.

Flushing the cooling system will not hurt anything no matter how many miles on the engine and in fact will likely help. Providing there where no leaks since the thermostat was replaced I still suspect you had trapped air and flushing and bleeding should take care of it if this is the case.But if flushing is not helping then, It is also possible the new thermostat was defective and possibly did stick shut. For no more than they cost it might be a good idea to replace it again just to be sure .

If you notice any rough idle and cold start problems then there is one more possibility to be checked.

That is CHT (cylinder head temp sensor).

It is possible if the CHT (cylinder head temp sensor) wasnt reading right, I would get the overheating issue resolved first and see it this issue returns. Engine temp can and does effect engine running.

This details will help.

Thanks.

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