1990 Ford Bronco Teperature runs from Lower to upper end of

PAUL ANDRESEN

MEMBER
1990 FORD BRONCO
V8
4WD
AUTOMATIC
119,000 MILES

I ran hot and blew my head gasket. I had new heads put on as well as new radiator and hoses. I drove Truck a couple of days ago and was running hot. The red light for check engine came on. When I got the Truck home I decided to swap out the thremostat. It had never been replaced by the mechanic when I had all of the work done. Now with a new thermo, ( installed facing the right way) max temp 195 deg. The gauge goes down to the N and runs up to the L back and forth like this. I also took the Truck out of overdrive RPM at 2500 and it jumped above the L. I am affraid to overheat this Truck again, the last time ran me over 3K. Any ideas why it is jumping around so much.

2 Replies

DOCFIXIT

MECHANIC
18,828 POSTS

If the engine is not getting hot my guess is the temp sender was fried on the overheat. Have you put a new one in since overheat?

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Friday, July 18th, 2008 AT 12:24 PM

RASMATAZ

MECHANIC
75,992 POSTS

Have it block and pressure tested-do the block first to pinpoint a combustion leaking into the cooling system or a gas analyzer to sniff for hydrocarbons at the radiator fill neck.

Pressure test: do not do a pressure test if there's leakage at the headgasket this might cause coolant into the cylinders and lock it up or bend a connecting rod if cranked thereafter. The headgasket should be repaired before doing the pressure test.

If the block and pressure test passes check the following: Thermostat, Pressure test the Rad. Cap, Clogged radiator, Fan clutch, Radiator electrical fan, collaspe hoses, water pump.