My trucks temp usually hangs out about halfway up the gauge. Occassionally it will drop down to a 1/4 and then slowly rise back up to half. No big deal. Well tonight it went all the way up to 3/4 and check gage light came on and then back off because the temp dropped all the way down to 1/4 quickly. It did this 3 times, it never got hot enought again to turn the gage light on but it did go up and drop down fast to 1/4 multiple times. This all happened within 10minutes of starting and driving. Then it rose to halfway and was fine for the next 10 minutes I was driving it.

My conclusion is the thermostat stuck. What's yours?

 

Agreed, the T-Stat is sticking or you have a cooling system leak. What level is your coolant at? Is your fan clutch working? Is your rad blocked? How is your Over-Flow container? Rad cap holding pressure?

Just give it a big check over before concluding the T-Stat, overheating a motor is never fun.

 

Everything else seems ok. Coolant is full, fan's working, over-flow container looks a bit gunky but full, holds pressure fine. I did put a bars leak in it awhile back, I believe that's why it looks gunky and maybe gunked up the t-stat. I don't believe the radiator is blocked as i get great heat and when I check the level it changes. I tried burping it last night and every 10 seconds a geyser of coolant shot out. I lost about 1/2 gallon of coolant this way. Then it stopped and I refilled it and drove around. Know it heats up to a little past halfway then drops and after a while it holds steady at the halfway mark.
I'm getting it flushed tonight then I'm taking it home and changing out the t-stat. I'll pay only $20 for the flush with the coupons I have but I'm not paying them $50 to change the t-stat when I can do it for $10 plus the cost of beer.

 

If there is no air in the system.. it's you stat.

Rich

 

Thanks.
I haven't changed my t-stat in awhile is there a gasket on the water outlet. I know the stat comes with the gasket ring but not sure of the water outlet.

 

if i remember right there is im pretty sure its premade but its been a hot minute since ive messed with one

 

Thanks. I'm almost positive there is one also so I'll have to pick 1 up.

 

Well I replaced the t-stat last night with a 198F. The flush is getting done tonight. The gauge now goes up to halfway and will sit there then shoot up to about 5/8 and then shoots down to about 3/8 before going back up to halfway and sitting there. better then before. It does this over and over again and each time the gauge doesn't shoot up as high or fall as low. Am I freaking out for nothing?
It is not technically overheating but I'm used to it just sitting halfway and this is freaking me out. Possibly some air in the system causing it to heat up quickly and when the air passes it cools right down. By the way I replaced the sending unit to the gauge while I was at it, only $7 so not that bad. Plus the engine seems to idle a little better, less roughness to it.

 

mine goes up to 3/4 then down to 1/4 it been doing that sice i got it about 8 months ago

 

Has the lower radiator hose ever been changed ? Sounds like it either is collapsing on you or a piece of the inner hose is flapping back and forth causing a blockage.
Same for the upper hose.

 

I wonder if the guage cluster is bad?

On my 06 (and most other cars sold in america) the temp guage is buffered from actual temps. They do that to keep people from "freaking out".

On my 06 it will reach it's "home position" in the middle at 170F and it'll stay there until 220F. Colder and warmer within that range **might** move the needle a hair either way. Can't really tell. But below and above that range and it clearly reads low / high.

Sounds to me like you need a scanguage. Use it to see what your trucks PCM is seeing. Which btw is a different sensor than the one the dash guage uses.

Rich

 

Not sure the last time they've been changed but it hasn't been in the last few years. After I flush it tonight that may be my next step.

I wish I could afford a scangauge, but swapping the cluster out will be a last resort.

 

Not sure the last time they've been changed but it hasn't been in the last few years. After I flush it tonight that may be my next step.

After you drain the coolant , pull both hoses off and check for any cracking or torn rubber inside .
If you find one crack or even a small tear , replace it.

 

I'm going to go ahead and replace the lower hose tonight. Thinking back it hasn't been changed since I had the truck, 9 years. The upper I just replaced this past summer when I changed my radiator. I didn't change the bottom one since no parts stores around here carry them and Ford was closed that weekend.

 

Flushed it and the lower hose changed. Still heating up a little higher then I'm used to. Could the 198F t-stat cause this? I also noticed that my belt tensioner is a little ****-eyed. If the belt is slipping it may cause the water pump to act up. Thoughts on this idea?

Someone told me the fins in the water pump could be damaged. I would think that I would always have a higher temp, not just occassionally if this was going on.

Went out in the bush today to hunt some deer and it rose up a few times but dropped right back down then held steady the rest of the day. And nope I didn't even see a deer today, just a flock of turkey and a bunny rabbit.

 

I was having this exact problem over the summer. My air conditioner would quit blowing cold air once i drove for a little while b/c the the guage would be a little over halfway. I'll tell you everything i did. First, i flushed the radiator REALLLLY GOOD!!! Then i added some anti-rust with the coolant. Well it was still acting up after this, so i changed the thermostat. After this, it never gave me another problem, except one time a sat in a drive-thru for awhile and it showed that my temp was high. That thermostat that you bought could already be bad since you still had NASTY coolant running through it. I would replace the thermostat again and then go from there.

 

No your water pump is not the problem.
You either have:
air in the system
it's your stat
Or the guage is not reading right.

Trust me... I was a water pump engineer for ford.. for six years. It's one of those three.

 

I'll start with air and t-stat one day this week.

Thanks