Overheating
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Overheating
Hey everbody I've got a 1999 Expedition 4x4 with the 4.6 EFI and it over heated one morning, just warming up in the yard. Well I did a flush an changed out the hose the hole 9 yards filled it up and let it run for an hour all was good drive it the day not problem the next morning got up to go to work got about 3 miles from my house an it started overheating. The thing I don't get is this I open the cap just alittle to let air off and the gauge goes back down tight the cap and go runs great let it cool off and run it again the same thing all over again. Is there certain way to fill the system? To stop this I've checked the fan, change the hoses and put 3 yes new thremostas in but for the life of me can not find the 
temp send unit senor 
any ideas?
temp send unit senor any ideas?
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Joined: Aug 2009
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Could be a few things. The possibility to fear the most would be a blown headgasket. Have you checked the oil to see if it has turned milky? Are there any signs of oil in the coolant?
Engine compression can pressurize the system and cause rapid overheating. That would be the headgasket.
Is it really overheating or is it a sender issue? You can generally tell if the engine is truely overheated. Underhood will be extremely hot, hoses will be way too hot to touch, expansion tank will be full to overflowing. Just having a little pressure in the expansion tank is normal.
I am assuming no coolant leaks and proper coolant level?
Since you have changed the thermostat, coolant and hoses, I would do a pressure test next.
Engine compression can pressurize the system and cause rapid overheating. That would be the headgasket.
Is it really overheating or is it a sender issue? You can generally tell if the engine is truely overheated. Underhood will be extremely hot, hoses will be way too hot to touch, expansion tank will be full to overflowing. Just having a little pressure in the expansion tank is normal.
I am assuming no coolant leaks and proper coolant level?
Since you have changed the thermostat, coolant and hoses, I would do a pressure test next.
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did you pressure test it hot and cold sounds like you only have a problem when it's cold then when the engine heats up it seals the leak put by this point it has already over pressurized the system so it overheats you then release the pressure and it's back to normal they nake stuff to check for the presence of combustion gasses or you could put your pressure tester on the truck and start it up if the gauge goes up fast means you have a leak, also it could be a bad cap not releasing pressure then when you play with it you temporarily fix the problem
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No did the pressure check cold didn't do it hot, I'm going by ford today and get a cap and see if that maybe it the new one I put on is an after market one, I let the truck run for about an hour to bleed the air off shut it down and let it cool and did it again just to be sure but I'm going to give that a try to. thanks Fordtech08
