Maybe that's when the air comes into the system and cools the temp guage?
Maybe that's when the pump stops pumping so it's standing water by the guage and eventually cools it off?

Just to clearify the amount of time between each symptom as they come.
From a cold start: Truck warms to normal temp like... normal.
About 4-5mins later, Truck starts to cool down, slowly cools down. Takes about 1min to reach C (Cold on the dash temp guage).
Stays at C for another minute maybe 1 1/2min.
Shoots up past H (Hot).
Stays for about 30secs, then returns to normal temp.
The heat coming into the truck acts accordingly except when after it overheats and returns to normal temp. Sometimes it goes back to warm but other times it stays cold. There is a faint warmth to it but it's still cold. (FYI: I live in Minnesota). When it's cold air coming through and the dash temp reads normal, it does its thing again... normal, cold, overheat, normal. Then there's heat coming through but one time it did it twice like that and it was cold air all the way home (about 15mile drive) and the dash temp was normal the whole time BUT my guess is that I may have been low on antifreeze at that moment. Not sure.

 

Welp... Found the problem... It's what we all fear I'm sure. Blown head gasket. Took it to Car-X and they did the pressure test and it was clear as day. They're asking for $2500 but I'm pretty sure someone else can do it for much cheaper or should I say less expensive Anywayz, thanks for all the help and to those that have this problem... Highly recommend it get it taken care of fast or you'll be buying a new engine!!!

 

Ugh! Certainly not good news.

Is the $2500 for a gasket replacement, or for a remanufactured engine?

Thanks for the follow-up on the findings. Always good to hear what the final outcome is, even if it's bad news.

 

2500 for gasket replacement. It's another 800 if the heads are warped or cracked BUT I found another shop by my house to do it for much cheaper... 1600, not sure what they want if the heads are warped/cracked.

 

@%&!*)

 

I just read the post from czecter01 about your odd cooling problem on your f150. Looks like an old post (4 years?) But I had to comment. It caught my attention because this is my problem exactly! I have a 98 f150 4.6L v8 It is doing the same thing down to the smallest detail. Mine is slow to warm up, then when it gets to temp the heater starts to slowly go cold as the temp gauge drops slowly then the gauge shoots up over the red for maybe a minute or so, then back down to normal and i get a burst of hot air from the heater again. Sometimes it will repeat this cycle once or twice before settling down to normal temp and heater operation.I have learned that these trucks have a system that makes them go into a 4cyl mode when they overheat. They will run on 4cyl to help cool the engine when overheated. when this mode is triggered the temp gauge goes all the way above the red immedietly. once there is sufficient cooling the gauge drops back to normal. this explains the gauge jumping up suddenly. but I still have the erratic cooling problem. I have replaced the thermostat twice, the water pump twice, flushed the system several times and purged the system of air in every way possible more times than I can remember with no results. I was just settling on the posssibility of a clogged radiator when I read in your post that you just put a new one in and it didnt help. Now I dont know what to try. I was hoping it isnt a seeping head gasket building up pressure in the cooling system and sapping the heads and block of coolant but Im running out of options. I thought it was a clogged radiator also because I can hear coolant gurgling in the heater core sometimes when in the cab.I did have the engine light come on while this was happening once. When i checked the code it said exessive cyl head temp. Also i am having alot of knocking and pingging when accelerating. Whats frustrating is that I have read many other post about people having this same problem with these trucks but nobody seems to have an answer. this seems to be a common problem. Can any one help???

 

The gurgling is exhaust gases from a bad head gasket probably. You have 14/16 PSI in the cooling system if it is sealed tight, but not that if the head gasket is leaking, then you have what ever the engine wants to throw into it circulating thru the system and forcing coolant out the overflow. This constant gas psi messes with the ability of the motor to circulate water properly and then messes with your head. Other problem with this motor is intake manifold and bolts bringing about coolant and vacuum leaks. Once the engine overheats head temp puts the rig in limpmode trying too cool off until you shut it off and let it sit. Some try a can of sealant in pure water to seal up for a cheap fix. I heard one guy say it worked for him. I never fixed one that way. It's always been a top end repair job and gaskets, bolts and sealer. It will get real expensive if let go too long, water getting into the cyl in enough quantity to cause a Hydroloc condition. This will bend a rod and do serious damage. Only way to keep from happening is to pull the plugs and turn motor over blowing out the coolant. Not a nice day. The gurgling continues until sealed by a good gasket clamp down.