i just got back from holidays in one piece,barely.i was pulling a 15 mile long hill with my 12000 lb 5er in tow.eng. temp. was fine.it went from 180-190 to 210-215 which is fine.the fan came on.everythings good but suddenly the gauge shot to max.[230]and stayed there.i couldnt pull over right away so i kept in it expecting a boilover but nothing happened.i finished the hill then the needle dropped suddenly from 230 to 210 then slowly cooled down.when i did check things out there were no signs of overheating.it happened once more on the trip.do you suspect faulty sensor,sending unit,thermostat,etc.thx for any help and soory for long wiinded story

 

Sounds like the thermostat stuck.

 

yea sounds like that too. if it happens again try turning on your heat in the cab. my dads 98 chevy dump with the 454 does that and he turns the heat on and it comes unstuck

 

it is the thermostat i had the same thing happen when i bought my truck they are like 20 bucks and a 10 minute change and youll be good to go

 

Think I've actully got a few in stock!