Temp gauge running hot

[Irish Pride]

Well, i got my 91 out yesterday and cleaned her up really good. i havent driven her all winter so i can keep the rust away. i let it idle while i washed it, then when i got in to drive around the block to dry it i noticed the temp gauge was at the very top but still inside the normal area. i sat and watched it for a minute and it never moved up or down. just stayed all the way at the top of normal. i take it around the block and as soon as i start driving it immediately lowers to its normal level about a third of the way up. get back home and put the brake on and idle and it starts rising again. i check the coolant and its fine. the fan was on and blowing, and the water pump isnt leaking anything. could i have a blocked radiator or could the temp gauge be messed up? any ideas??

 

[93rev2sev]

Temp guage could be messed up, but I usually see this when there is low coolant in the system. I know you said you checked it and it was fine...so here's a few other things to check.

After turning it off, how long does the upper radiator hose stay pressureized?

How old is the water pump?

Remove thermostat, stick it in a *** of hot water on the stove...use a meat thermometer to monitor the temp and make sure it opens completely and when it's supposed to.

 

[sperold]

Nine times out of ten it will be the thermostat. Do the test, but have a new one ready to do the test as well.

 

[Irish Pride]

What temp is the stat suppost to open at?

 

[SHOtime2511]

IIRC 192
some people swap to 180 degree t stats.

 

[93rev2sev]

It better be fully opened by 200° for sure. If it continues to move after 200°, then it's fuxord, I'd say.

 

[itwonder]

Sounds pretty normal to me if you have a 192 degree t-stat. Might change out the cap with a new Motorcraft one and pressure test system to be sure.