I have a 2000 Ford F150 5.4L 2V with 93000 miles. As of recently when I start the truck I can hear coolant bubbling through the heater core rather loudly. After driving a while, whenever I come to a stop light the heat goes cold. Yesterday I checked the overflow bottle and noticed it is sludgie from oil. It was also down almost a full gallon. I just recently had radiator flushed and filled. I have checked compression and all cylinders are good. No coolant in oil. New intake manifold and gaskets less then 500 miles ago. New plugs and COP's less then 1000 miles ago.(properly torqued) New IAC valve and EGR valve 50 miles ago. No loss of power at all throughout range, no hesitation, no missing. I have read a few articles about possibility of oil cooler adapter seal leaking. Would this cause this problem?

 

if you have oil in your coolant it sounds like your oil cooler has failed. the oil cooler is usually made into your radiator

 

Only the trans cooler runs through the radiator.

The brown gunk you see in your bottle is probably hard deposits from before your flush. Could have also came from your heater core after the flush. Unless it smells like exhaust gas, I would not be concerned. I don't think it is oil and is somewhat normal depending on what coolant you used and how long it was used.

The bubbling sound seems to me like you have air trapped in the system.

A bit concerning that you were a gallon short..... no visible leaks???

 

No leaks in the system. Decided to replace the radiator since there was quite a few dinged sections. After pulling it out I did notice a lot of buildup on side with trans cooler so a possible leak there. I already had a replacement gasket for the oil cooler adapter so went ahead and replaced that also. Flushed the system and back-flushed the heater core. So far everything seems to be working fine in that department. Now I notice that when in park if I rev up to 1500 rpm as soon as it hits 1500 it will drop suddenly around 200 rpm. No codes as of yet. Any thoughts?

 

FYI... total cost to replace radiator, flush system, replace oil cooler adapter gasket, and replace antifreeze $231.30

 

After reading another post about cleaning the MAF sensor I went ahead and checked mine out. It was really dirty so I followed the write-up and cleaned it with some Lectra-Motive. No more problems at 1500rpm. Still a slight erratic stumble at idle though when in park.