Cooling problem...or not

[DB_1]

Ok...i have a 97 Ranger with the 4.0 engine and last fri i had a little bit of a scare on my way to work. I came to a stop at a red light and the temp gauge caught my eye as it was in the red zone and t he "check gauge" light came on. Light turned green and i went ahead and was going to pull over asap to shut the engine down but the gauge went back into its normal range and the "check gauge" light went off. Thats the first time thats ever happened in the 6 yrs i've owned the truck. The needle on the gauge has always rock solid in the middle of the gauge no matter what i was doing, off roading, stop and go traffic...whatever.

So anyways first instinct was to check coolant level and it was fine, then I tested it to see how strong it was and it was fine. Next thing to check is thermostat to see if its stuck closed. Service manual says to touch upper rad. hose to see if its hot after warm up and it was.
Then I thought it could be hot because of the engine heat so thats still iffy. Other possibility could be temp gauge sending unit just above the T-stat.

As it stands, the temp gauge runs about 3/4 instead of the 1/2 way mark but it hasnt gone into the red again.
I'm gonna change the T-stat and coolant to see what that does then try the sending unit.

 

[Robb]

I think your t-stat may have gotten stuck there for a minute, then freed itself.

 

[DB_1]

Possibly...just when should you change a T-stat? The service manual and the owners manual doesnt say anything about it. I would imagine it should have been changed around 30 to 50k as preventative maint.

 

[Robb]

I usually just change mine first thing whenever a heating problem begins to show. It is cheap to do and a good excuse to change the coolant.

 

[Alec]

If you change the tstat go ahead and change the radiator cap too.