intermittent heat

[halls51]

Folks, I did a search for this and found zilch so here goes.

I have a 2000 Exp XLS 5.0 V6. I do have a CEL for codes P0171 and P0174 this is left and right banks lean. It is still too cold for me to go out looking for vacuum leaks (probably the PVC elbow) so that can wait a little longer.

Here is my conumdrum, After warm up the heater works fine. After a few miles it blows cold air in a few more miles it blows hot again. Its is driving me crazy.

Last year during the summer, I changed the thermostat and both temp sensors and burped the engine so I don't know what to do next.

If it were the thermostat seems it would be cold or hot all the time not just sometimes.....Exp does have about 150,000 miles on it.

 

[sidd2v]

Same thing was happening to me a few months ago. My water pump was failing. Replaced it and no it's fine.

 

[1996BLKBauer]

The thermostat should not be an issue, the heater core, which provides heat to the passenger compartment, is actually behind the thermostat. the waterpump simply pumps coolant through the heater core, until it reaches a certain temp. then the thermostat opens and then it goes though the rad. If it wasn't, you would not have heat for something like 30 minutes. Start with simple things, like is your coolant low?

 

[radman]

It can still be a thermostat

Some thermostats can be bad right out of the box. They can stick open or stick closed or can be very lazy going both ways. How does your temperature gage read when this is happening? If it is also fluctuating check the actual coolant temperature reading. If you do not have an infer-red heat gun just lightly touch the upper radiator hose with your hand, you will not hold on long if the thermostat is operating (195*) properly. If the heat is correct at the top radiator hose check the heater hoses where they enter the fire wall, both hoses should be hot. If they are not check the heater control valve in that same area.

If all is correct under the hood then it is time to check your heater box, blend door for operation or you AETC for proper functioning.

 

[corkey]

check the coolant level again, bet it's low again,,

sometimes the burp doesn't get all the air,,

 

[halls51]

Thanks for the inputs.. The thermostat was changed over a year ago and I have not had problems till now. I don't think that this is the problem though. The temperature gage is constant during this hot cold cycle but you have to remember that there are two temp sensors on this vehicle. I will check the other things and post again later. It is a rainy weekend here and I'm not going anywhere anyway.

Thanks