Hi all. I am back to having problems again with my 98 F150 4.6. About a month ago I was driving and peeked down at me temp gauge and noticed it was climbing fast up to H. I was at a stop light and just put it in nuetral and revved it a bit and it dropped back to normal within 5 seconds. I did pull over and check everything though and nothing seemed to be out of the ordinary. One time incident. Latley it has done this more frequently but never seems to last long. The other night I was driving home and it did it and when I put it in nuetral it revved up itself to about 4k RPM and stayed there. I immediatley pulled over, shut it off and restarted it and it was fine again. I have also noticed a strange alram or buzzing sound coming from the driver side maybe under the dash or very back of engine compartment only when truck is running. Kinda sounds like a shorted out door buzzer or headlight reminder buzzer. May be totally unrelated. Anyway, I did fill my overflow up good and hasn't overheated yet, although I really don't think it is REALLY overheating anyway. Now I have a constant CEL and a Cylinder 4 misfire code. The truck seems to misfire at idle and up to about 15 MPH then runs smooth form there. Also noticed pleanty of white smoke out the exhaust this AM while pulling a trailer. Headgasket going or something different. It is getting cooler here in the mornings say around 50 or so, only see the smoke for about 3 minutes thens clears up and never see it again. Any Ideas?

 

It just dawned on me. Is it possible to hear the head gaske t leak? That sound I am hearing, could that be the pressure escaping and thats what I am hearing?

 

check your dipstick - how does the oil look?

 

The oil looks fine. Just changed it about 2 weeks ago and still looks fine. The old oil was just dark and no soapy or frothy look to it. I have been adding water to the radiator quite often when it seems to start to overheat lately. Strange thing is it must be going out the exhaust because I sure can't see it leaking or in the oil. This has me baffled.

 

I had a '96 grand prix with the 3.1 v6 in it that did the same thing - I ended up scrapping the car never found out what the problem was with it. I suspected the Lower Intake Manifold as that is a sore point with those engines but it never leaked into the oil/crankcase so I was in the same boat as you.

Hopefully someone else has some relevant information to share with you.

 

Obviously constant adding of coolant isn't good. Have someone do a block-check of the system. It is a test where by the air in the top of the radiator is drawn thru a liquid, blue in color and if CO2 is present the liquid will turn yellow. Another test that can be done is to remove all spark plugs and pressurize the radiator. If a pressure drop is noted, crank the engine over with the starter and see which cylinder or cylinders pushes water out the spark plug holes.

 

Another thought, it wouldn't surprise me to find out your #4 cylinder with the misfire has the bad head gasket.