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How are you getting the coolant temperature reading? Unless it's a manual transmission, the coolant temperature isn't even monitored by the PCM.
im using an ae. it has a engine coolant input. im guessing it is reading it but not sure. came back just now and truck is doing same thing. I started with tank half way down. fluid came to top. I shut it off 3 times to let level go back down. once thermostat opened around 200 oil temp level was ok. it just climbs until therostat opens. I know it will some but not this much. wonder if a plugged oil cooler can cause a problem? it just acts like the coolant isnt coming out of engine. both hoses and coolant are cold until thermo opens. thanks for the input.
im a 1 1/2 inches below the min mark. about 3 from top. still coming out. im thinking about getting kit to check for gasses in coolant. kinda lost right now.
All of our trucks have the Engine Coolant Temperature available on the software, but only specific trucks have the sensor on the OBDII port. When I look at my ECT, it starts at 300, then it drops down, then it climbs to some mystery number that has no direct correlation to the actual coolant temperature. I had a boilover reading on ECT with AE one time, and two different laser thermometers agreed my coolant temp was 165 degrees F (winter).
I now disregard that "sensor" on the list of available PIDs.
That doesn't necessarily mean you need to pull the heads. That means you had the system completely closed off and the expansion of the air and liquid in the system had no way to relieve the pressure. The cap relieves that pressure when it reaches 16 psi. To do a cooling system pressure test, you pressurize the system with the engine cold and off and see if it leaks down over time.
Don't pull the heads just yet. Besides, they are about 200 pounds each. The likelihood of a blown head gasket is all but non-existent. Cups, however, are a whole 'nother matter. That picture in my first post is from combustion gasses getting into my coolant, from a damaged cup and a loose injector. A bad cup and a bad copper washer on an injector can do the same thing.
If you were to pull the heads, you'd have to do a lot of tear-down. Before digging too deep, you can pull the injectors and inspect the cups. A problem this big will be obvious - mine was very subtle and harder to spot.
I recently had a problem with coolant blowing out of the degas bottle the bottle was completely full. I changed the cap and now all is well. If it is a Dorman mfg degas bottle, the threads are a smaller diameter then the factory bottle and the cap may not seat correctly.
I'm with rich on this. If it were a head gasket I think it would pressurize the system to the point you would loose a lot more coolant. cylinder compression runs around 400 psi.
When my semi had a bad head gasket it would empty my reservoir about every 600 miles and started blowing heater hoses and radiator hoses. I know the radiator cap shouldn't let the pressure build that high but maybe old hoses contributed to the problem. And it had an overflow similar to the ford degas bottle.