This is driving me nuts. So after a week of fiddling and searching through three different forums I decided I might as well make a post and see if someone else has been in the same boat.

I bought my truck with 75k just a little over a month ago. Added K&N intake and just got the exhaust done along with a few other things. In all the excitement of having a new truck, I didn't notice my plastic coolant tank run dry. I sure did notice the temp gauge climb to 3/4 about 4 miles from home though.

I turned the heater on to full blast and checked under the hood, sure enough the plastic tank was empty.

One mile towards home and the temp had dropped to normal. Got home, filled the tank and cooled her off. Started off again and she went up to 2/3-3/4 again and then immediately leveled back down to normal-ish about 1/2 on the gauge.

I figured must be an air bubble, so after driving around a bit I get home, look up the burping method and go give it a shot. I get a couple-three hiccups and figured she's got to be good. Same thing tomorrow though. Tried the burp again, didn't notice anything at all. (Then again not sure if I'm leaving it idle long enough).

Just to get it out of the way, I replaced rad cap and the IAT the next day, with no change. I have a thermostat ordered and plan to do it tuesday when I have a friend around to give me a hand. Hoping while while the housing is off we can inspect the water pump and ensure it's functioning.

Last couple of days I drove the car instead. Today when i got back home I decided to research the fan clutch to figure out how you determine if it is functioning. It spins freely while cold, and freely while engine is the current normal-ish temp. Which is slightly hotter than it used to be. I did this after it letting idle with the front end up and rad cap off for at least 30 minutes or so.

What had me convinced that my issue is the thermostat is that one the initial peak has been hot the truck will not fluctuate very much and will not overheat while idling for long times.

I think that's the gist of it, I hope some of you guys with more experience can point me in the right direction.

 

It's easy enough to check the t-stat, and you don't need help with it, it's right at where the top hose enters the engine, real easy to get to.

Remove it and drop it in a pan of water that is over fairly high heat, if the water reaches a boil and the thermostat hasn't opened, it's bad.

 

Even if it pops open, I'd replace it. It might be intermitent for some odd reason, partially open..etc
You need to idle for quite a while to burp the system. For atleast 15-20min after it gets up to temp. You had the actual rad cap off right, not the reseviour cap? Air can't go downward.
Also, I just seen thread the other day about guys saying aftermarket rad caps have given them problems and they had to get the exact one from the dealer before their problems went away. Just throwing it out there so your not chasing your problem all over and overlooking anything.

 

Some vehicles are hard to get all of the air out. It usually takes 2 or 3 times to get my Mustang air free. How much air is the fan moving? The fan should be fairly tight when cold and the fan is usually rather noisy for a couple of minutes on a cold start up.

 

Thanks for the input. I'll give it another shot of burping today. I'm not sure where the oil pickup is in these engines and if having the front end raised 12-18 inches is having any effect. So I plan on double checking the oil level first.

Does the thermostat have a gasket or do I need to buy some permatex gasket maker or something? It looks like a real easy job, but after I slipped a disc in my back I'm more cautious about stuff. I don't want to start something I can't finish and have to be the guy who paid to have a tow truck haul it in to a shop.

 

Mine started opening slowly and late. I just replaced it with a 180. Done and done.

 

My vote's for t-stat. Should have a gasket on it already , pop the old one out and seat the new one all the way in. Make sure to test the t-stat in boiling water, but if you're at high elevation (I'm at 4500 feet) you'll barely see any movement in the t-stat, but it will move a very small amount. Water boils at ~95 degrees Celsius where I'm at.

 

Got 'er done this morning.

Stupid thermostat came apart. It must have been wedging from the pressure causing the weird temperature spikes.

I'm not sure if it's a factory or aftermarket, because I could see that the hose clamp had been moved before.

I'll post pics of it if anyone wants to see.