AcesHigh

My 5.4L is doing the same thing that I've read in a few other posts:

Heater slowly warms as engine temp comes up to operating temp. It then cools off and feels like it is blowing air conditioning air. The engine temperature starts to spike and end eventually drops suddenly and I get heat out the vents.

I have done the following:
1. Replaced thermostat
2. Pulled thermostat to check it in boiling water
3. Drained coolant including pulling plug by freeze plugs.
4. Refilled with vacuum system although I couldn't get the vacuum to 20-25 in/Hg as suggested on the vacuum.
5. Tested for CO in coolant reservoir tank with test kit - negative results. I may redo this test.
6. Put radiator flush kit on heater hose and filled with coolant from there with the hose completely above the engine.


The heater hose coming from the heater core is not hot like the one feeding it, but how would that have any relation to the temperature spike issue???


I'm thinking about back washing the heater core tomorrow. I may pressure test the heater core if I can find a test kit at O'Reilly's or somewhere.

Any ideas?


I've read quite a few posts about the head gasket issue on these trucks. That's why I did the CO test. Do I need to put the truck under load when running the CO test?


Mark

AcesHigh

Bueler? Bueler? Bueler?

Any suggestions or ideas?

Would the heater core being completely blocked (air locked or sediment) have anything to do with the temperature spike? Doesn't seem like it.

Frank_Ford

It sounds like you have a blockage somewhere in your system. You seem to have done all the correct things. I am thinking that you may have a blockage in your engine block but I cannot tell for sure. Has your cooling system been maintained in the past? If no, good chance that block is heavily rusted and creating blockage.