I have an odd issue with the cooling system, i have about 190k miles on the truck now, and am about 1600 miles from home. Before i left on this trip my truck was running hot, never completely overheating but running about 30 degrees above normal, somewhere around 245ish. i thought maybe the water pump i installed last year had crapped out so i changed it again, and although the bearing were starting to to go bad, stupid autozone parts, that was the problem, so i pulled my radiator and had it corded out at reputable shop, i thought that fixed it so i left for my trip, now the fu part. about 6 hours in it starts getting hot again, well crap, i talked to my dad while driving and we figured out if i turned the heater on then it would start to run cooler again, so i got to my parents, and decided to flush the entire system, twice.

Well it didnt work, at idle it will stay a constant temp, but once its at anormal temp and i start driving, mostly highway it will get hot, so then i turn the heater on and it cools down, then i will drive through rain and it will drop to about 180 or less, and then i hit a hill and downshift, and it spikes back to 240. I changed the thermostat when i did the water pump, and then again when it was doing it again.

Im not sure what to do next, someone said that maybe my radiator is just shot, possible but i dunno. Or maybe its my clutch fan? but dont they just spin at a constant speed when goin 70mph on the hwy, and with that amount of air flowing into the engine compartment? im not sure. maybe the gauge is just freakin out, but i doubt that.

Sorry about the length of this, but i need as much help as possible.and any help will be good help. Thankks for your time guys and your advice.

 

With it cold the fan should spin freely, with it hot you should feel some resistance. And remove the belt and see if it's wobbling around at all.

And if you normally are running @ 215, that's not right. What brand t-stat did you install. And it could be just the sending unit, and you can test it with a meter and a manual.

 

its a 180 stat that i picked up at my local auto parts store, i used the same kinda last year with no problems. my normal temp is about 200 or at least it was before all this starting happening, at the most last summer i would see it get to maybe 220ish. With the stock gauge is tough to tell exactly wear the temp is, but it shouldnt fluctuate nearly as much as it is. Yesterday in only about a 60mile trip i saw temps ranging from almost redline down to 175, that was in driving rain through the mountains in virginia, air temp around 75.

i will check to see if the fan is wobbly, ive had it off two or three times since this has started.

 

Cold he have a bubble in the system, Or the fan clutch is going out? It is very odd that the temp picks up on the highway and not in traffic!!!

 

Could be more serious obviously, but I'm thinking sending unit or a Tstat problem,maybe even as simple as the rad. cap. are you sure the radiator and tanks are full , and you're not loosing coolant?

 

Ok I just need to make sure you are putting the t stat in correctly?

 

im not losing coolant, and i have checked for bubbles in the system. radiator is full, tank is full.

why would it run significantly cooler when i heater on. i know the coolant gets to flow more that way, but it shouldnt cause that much of a difference i wouldnt think. when i turn it on heat within about 1min the temp can drop 20-30 degrees

 

I would take the radiator cap off and run the truck till it hits normal operating temps and t-stat opens. Watch to see if the coolant is moving or not. Also I would check and see if the hoses are open and not clogged, it has happened. Like others have said check the clutch fan. With engine off spin the fan. It shouldn't spin more than two turns if that.

The radiator cap is a possibility. I had the opposite problem with my truck getting hot at a stop. The rad cap would allow coolant into the tank but not back in to the radiator.

I would either replace the temp sensor of install a mechanical temp gauge temporary and ensure the dash is giving you correct info before dumping anymore money into the truck.

edit: reason for temp dropping when heater is on is because your increase the distance the coolant has to flow allowing it to have a bit more time to cool as it cycles.

 

+1..........

 

i replaced the radiator cap only a few months ago, the old one had been leaking. I went ahead and ordered a new fan from napa after talkin to a few mechanics and the guy at napa. if that doesnt fix it, then i will just have to limp it home where i will be able to really get a good look at it. I appreciate the responses and now have a better idea of what to look for.

the upper radiator hose is brand new, and the lower is pretty new, i did check to make sure they were not clogged, they are not. the system has been flushed several times recently. the lower hose is flowing properly as well.

as far as letting it run with the cap off at reguar temp, i have done that several times, to verify that there is not any bubbles or air in the system. I really hope its just the clutch fan.

if it doesnt fix it, then i will put on a temporary aux temp gauge to verify the readings, but i dont have the time to do that right now. im supposed to drive from Virginia to oklahoma on saturday.