Got an 08 Stx 4.6 Ltr....truck has been recently making loud noise from passenger side engine. Sounds like the RPM's are through the roof but when you look at them they are normal..maybe slightly higher. Real loud at first then with each shift it lessons. Sounds almost like air coming back into the engine. Funny thing is it does this maybe for a little while (10-20 30 miles) then goes away for days at a time. I would take it to the dealer but it is so intermitten that I am afraid they wouldn't find it. Also I run it on dual fuel (propane + gasoline) that they would for sure blame the cause on that. It will make the noise on either fuel. There is no hesitation and for the most part the power is still there. Not sure where to look...but was thinking EGR valve?? bad cat??? IAc valve...Vac leak??

anyone??

 

sure its not your fan on your radiator, you know you fan cluthc is engaged

 

No, definately not the fan..i have had this truck over a year and it just started. Almost sounds like a jet engine when you hit the pedal...as if the rpms are at 5000 when they are showing 2500 to 2800 on accel

 

hmm interseting, youll just have to narrow it down from the engine bay nad go from there, get someon to hit the gas or something for you when it starts and listen

 

my dad had a 99 4.6L that did a similar thing, and like you said for the first few miles it sounded like a jet engine, but it was just the fan overspeeding, the clutch was stuck. like ford4wd said just check it with someone else revving it and see if the fan speeds up.

 

yeah I think you guys are right...it looks to be the the fan clutch. I opened the hood and the fan was spining so fast it felt like my hat was going to fly off...it is an intermitten thing....you think the dealer could find a fault when it is not doing it???