hello all! i am new to this site but not to the truck. i just recently purchased my very own 2004 f150 lariat. problem is that after my first oil change i got the diesel sound. and in the last 1500 miles it has gone from barely noticable to sounding like a cummins! ( a little dramatic) anyways i am just trying to figure out how long i have mefore an overhaul is in order. i did a tune jst before the oil and it was running great. still is its just really annoying. i had a yellowish foam surrounding the oil fill cap not sure what that means! any thoughts would really help!

 

What oil with what filter did you use? These 3vs need 5w20 to run well with a motor craft FL-820s oil filter which has an anti-drainback valve.

Yellow film under the oil cap usually indicates you take too many short trips without the engine being fully warmed up to temp ( 2 miles down the road, then park/shut off ).

 

That foam could also indicate failing PCV valves. Like Darren said, make sure the correct oil is in there before you destroy the mains. Use the motorcraft 820 filter. If you didn't put in the correct oil and filter stop driving it before you hose yourself. If the wrong oil was used it may be to late. Dieseling is also something that happens with **** poor fuel or timing gone wrong.

 

Yellow film surrounding the oil fill cap. Like on the outside of the filler neck or cam cover ? Under the cap is normal. Which oil did you use, - should always use the recommended blend in cold claimants, - a switch to full syn creates the most blow-by, plugging things up and at times, freezing them.

All posts are good, - so....What did you do? Yea, a correct oil filter is a must.