Ok im going to try and make this clear as possible. I just bought a 97 f150 4.6 triton 4x4. I ran and test drove it for atleast an hour had no problems except codes for egr and an o2 sensor. I drove it 88 miles with no problems what so ever. The next day i got in it drove probably 5 miles and heat went to cold, and was pouring coolant out of tank. but did not overheat. gauge stayed a norm op. I pulled over shut the truck off took cap off and let set for about 10 minutes. cleared the 2 codes got in started fine and drove for about another 5-6 miles no problems at all, heat was hot. parked it got ready for work got in it and drove about 3 miles and heat went cold, again temp gauge read good, and this time it wasnt pouring coolant out( which after the first time i filled back up) but there was pressure on the cap. so I shut it off let it sit for about 10 minutes got in took off for work heat was warm still not overheating. made it to work fine. I put a new cap on and tested the old one and it wouldnt hold pressure at all. I leave work about 2 in the am and drive about 5 miles and temp gauge pegs out for about 5 seconds then back to norm op range. but check engine light was flashing and started running rough. so i pulled over to get gas anyways and i took the cap off and let in sit. put cap on started temp gauge was in norm op range, but still running rough and a lifter tapping. I nursed it home and parked it. got up today to flush coolant system and change thermostat and each time ran it atleast 30-40 minutes never over heated didnt pour coolant out but still running rough and lift tapping. I checked oil it was about a quart low so I added a quart and some stp oil treatment and continued to flush system. still rough running unless you get into the throttle pretty good then it runs fine until you idle but never tried dying, still lifter tapping. any Ideas where to start? i think i know what most will say and what someone will know exactly but im hoping there might be something else wrong with it. and how do i fix the lifter tapping? also how hard is it to swap the engines a 4.6 for a 4.6 or even a 5.4? what all will i need, need to change etc. I wont be pulling the trans if i do a motor swap

 

Does the coolant smell like exhuast?

 

So since you changed the stat, - the cab heat and over heating are no longer an issue?

You don't have lifters, - lash adjusters only.

Being that it heated like it did, it's to hard to determine what damage was done. You may have gotten lucky, - time will tell.

Check all the plug chambers for coolant, -specially #5-#8. Check the others as well and blow them out with compressed air. Take the coils apart for any wet chambers you find and dry them out as well. Do that for now.

And DON'T clear any more codes. Write down exactly what they are first...The numbers.

 

Change the oil to 5w30, and get that STP oil treatment out of it. That molasses does not belong in a modular engine. Use a Motorcraft filter also.

 

Check idle air control valve