98 f150 v8 4.6L
Recently I've been getting fluctuating temperture readings from the temp gauge on the dash and my heat would go cold after the truck had been running for a while on the highway. The temp guage would go from normal temp to cold and then suddenly hot! and then back to normal temp. So I flushed the system with prestone super flush and changed the thermostat and replaced the radiator cap. I still have the same symptoms as before except now radiator fliud likes to spill/shoot out of the cap I just bought. I have tried the old cap and it does the same thing. It doesn't seem to shoot radiatior fluid out after it does it the first time when I refill it. Also, one other symptom I forgot to mention, even though the temp guage reads normal, the heat coming through into the cab turns to cool. It seems after i give it a little gas that it comes back on again. I'm thinking now that it's the water pump but I looked in the service manual and it says the water pump is good if there is no anifreeze coming out of some sort of spout either on top or bottom of it and it is not. So what's happening here?

 

I have the same exact problem. I haven't started any problem shooting, I was going to start with a thermostat and hoping to get lucky. So if anyone has any answers that would be great.

 

Hey guys, I am having the same problem. 1998 F150 4.6 L V8. I changed out the thermostat, no good, flushed coolant system and replaced it, no good, put aluma seal in to see if it was a leak or something, no good. My next thing will be to change the water pump just to make sure. If that doesn't work, I will be changing out my heating coil. I dont get great heat either. If that doesn't work, I will have to assume the worst, it may be a blown head gasket. The good news, there is now the liquids which are a permanent head gasket repair instead of having it taken out and replaced. Hope this helps, if not then I need some help too.

 

I'm having a similar problem. 1999 f150, just had the heater core replaced. I was not having issues before that. Now if I start up and hit the highway the air warms along with the engine temp. Suddenly, the air will go cold and the temp gauge rises. I've had it go back to a normal temp before without doing anything or relieved the pressure through the coolant fill resevoir as I have noticed the upper hose is cold and rigged. After doing this, I could drive long distances without any reoccurence. Also, I have removed the thermostat and it will run fine(with a little cardboard for my manual thermostat). Also tried burping the cooling system(closed) to no avail. I also put in a new radiator....to no avail. There had been a large amount of rust in the system so I figured it couldn't hurt to do this as the new radiator weighed in at 6.8lbs. the old one weighed 18lbs drained!! 2 new thermostats and upper hose and radiator later ... still a problem. No oil or bubbles in coolant and no coolant in oil and no exhaust fume issues. Truck runs great except for this enigma!!

 

One of the common problems after draining the cooling system for repairs is trapped air in the system. There are several ways to correct this and one of the ways is to remove one of the heater hoses, preferably the higher one just enough to allow the trapped air to exit. The ideal way would be to do it when the engine is running, but one has to be careful of moving pulleys and belts. There are other ways such as applying vacuum to the fill hole, but most people don't have that kind of equip avail to use. Next best thing is to remove one of the hoses at the highest position and allow the air to go out. This is one of those times where patience helps a lot.

 

Keeping my fingers crossed as I have had no more problems since I did two things. First I drilled a 1/16th inch hole in the thermostat on the stopper. Then I filled the radiator by detaching the upper hose @ the radiator using a funnel attached to a chunk of gardenhose. Next I filled the upper hose to capacity and pinched it then shoved it back on the radiator(yes spilling a little but not too much). I've driven it Several times with no more issues.

 

Thanks Hanky!!! Now to tackle my sticky brake issue. When I first start off my rear brakes sometimes lock up when applied.

 

I don't know which one of these could be causing the problem, but if I leave anything out let's hope someone will tell us.
If the problem is confined to only one wheel you might have to remove the wheel and confirm that the hose/line to the wheel isn't pinched or with a partial blockage preventing the fluid from returning to the master cyl and releasing the wheel cyl /caliper. Last, make sure the piston(s) are free to return to the released position.
If it is both wheels the problem most likely would be further up toward the master cyl.
If the master cyl was replaced and the activating rod from the booster doesn't allow the pistons in the master cyl to return to the full released position it could cause the brakes to drag. If the parking brake cables are staying applied that could contribute to the problem. Lastly the hose from the body to the rear axle might have a problem preventing the fluid from returning to the master cyl and holding the rear brakes applied.
Also , make sure no hardware parts are missing or broken.
Make sure whoever replaced the rear brakes in the past assembled them correctly.
Check for any fluid or grease getting on the braking surfaces.
If all that is OK there is always the proportioning valve.

 

My 98 F150 does the same thing. I didnt have this problem until I replaced the brake shoes. Im pretty sure that the self adjuster in the brake hardware is bad causing my problem or I adjusted them to tight when I replaced the brake shoes. I find that if I have a load on my truck they dont do it near as ofter. Waiting for a dry day to tear back into mine to find the problem. But if your truck has disc brakes I would check everything that Hanky mentioned. Just a thought