Alright folks, it's time for another installment of 'My old broken truck'

97 F150 v8 4.6l

So yesterday when I drove to work (about a 15 min drive) the oil light came on as if there was no oil/low pressure, but the gauge showed that l/h was good. The engine temp gauge dipped to right below normal operating temp and then immediately flew up to overheating, which put it into failsafe mode aka limp mode. I pulled over, and watched the temp gauge fall right back to normal range. Check engine light came on but everything else shows normal. I've been reading some posts about the thermostat and CHT being the culprits of a false temp readout, but I can't seem to find the CHT on this beast. This happened on my way home again that day, and both times today. I don't even know where to begin on this. Any help is appreciated!

 

What color is ur coolant right now, normal neon green or a rustic brown sludge? And how often do u change ur coolant?

 

Coolant is neon green. I change it yesterday, along with thermostat and ect sensor and switch. Still no change. I ran the truck with heater on high and degas bottle open to force any air out of the system. When I turn on the heater there is hot air and coolant level drops. When I turn on the a/c, the coolant level rises and pressure builds. When I relieve the pressure, the coolant level drops and stays way below the cold fill range. If I rev the engine while the a/c is on and degas bottle is open, the coolant gets displaced from lower hose, but stays about the same level. If degas bottle is closed and a/c is on and truck is revved, the level rises. Then drops once I turn the heater on. I don't even know where to go after the thermostat and ects. TIA!

 

Before u changed it was it brown? Because It could be ur water pump , that's what I had my issue with last yr it was corrodied down to where there were no blades to circulaate the coolant enough to keep the engine from over heating

 

I don't believe so, because if the water pump wasn't working, the coolant wouldn't move/displace at all, would it? Also, the coolant was neon green when I changed it as well. I do get some white smoke when I start her in the early morning temps (~48 degrees) but I really hope that was condensation and not coolant leaking into through a busted head gasket. But, when I start her in the mornings now (~74 degrees), there's no white smoke and no loss of power, except right before the overheat. I've only gotten the overheat when I run her from a cold start. If I drive her from any temp besides the block being cold, I do not overheat. I'm going to try letting her get completely up to operating temp from a cold start and see if she overheats again tonight.

 

Before u changed it was it brown? Because It could be ur water pump , that's what I had my issue with last yr it was corrodied down to where there were no blades to circulaate the coolant enough to keep the engine from over heating

 

The coolant was still neon green.

 

Have you checked your oil yet? The water pumps rarely fail on these models. Make sure it doesn't have a burnt smell to it, I may change it just for good measure.

 

I literally changed the oil two weeks ago. Even now, it doesn't have any signs of head gasket leakage (i.e. coolant/water coming out before oil, frothy texture, etc.). What would it be if the oil smells burnt?

 

Could be the oil pump if smell burnt oil and see a pressure difference. The guages arent that accurate, but if they go from one extremem to the next, there is usually an issue. Pull out your PCV valve and check on top of the valves for a burnt smell.