Heating up 86 BroncoII
New User
Joined: May 2002
Posts: 13
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From: Calgary Canada
Heating up 86 BroncoII
I have a 86 BroncoII 2.9 196k I have replaced the rad, water pump & the thermostat. I have noticed that it starts to over heat then it drops down. Then it goes back up, this has started more in the last couple a weeks. I will get off the highway and it will read almost up to the red line about 3/4 ways up drops to the 1/4. What the hell is going on ? Am I going to have to get my heads done?? When I last changed my oil it did not have any anti freeze in it. It is not leaking it any where.
Freshman User
Joined: Mar 2002
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Heating up 86 BroncoII
You might test your radiator cap to verify it has the correct pressure and pressure test the system while you are there. You might also flush the system with some Prestone flush. Make sure you have the correct thermostat, a lower temperature one might also help. It is possible your sensor or gauge is just not working correctly. I do not know how to test. It is still possible your new thermostat is not working as it is supposed to. It can be tested by placing in a pan of water on the stove and with a thermometer that goes up high enough, find out when the button actually opens. Test your fan to make sure it is bringing in air and the radiator is not restricted in any way.
It would seem to me to have such a swing in temperature, either the thermostat is not opening correctly or the gauge is not working correctly. You might make sure the thermostat was installed correctly. If you put the new one in the same way it came out and it was wrong before, it could still be wrong. Probably not, but easier mistakes have been made.
It would seem to me to have such a swing in temperature, either the thermostat is not opening correctly or the gauge is not working correctly. You might make sure the thermostat was installed correctly. If you put the new one in the same way it came out and it was wrong before, it could still be wrong. Probably not, but easier mistakes have been made.
Elder User
Joined: Aug 2000
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From: home
Heating up 86 BroncoII
I vote for air in the system. I have had this happen on my 89 B II (new rebuilt engine, radiator, heater core, hoses & water pump), 93 Aerostar 4.0 and 92 F 150 with 5.0. In the morning check the radiator & overflow tank and make sure they are full. It may take 50 or 100 miles to get the air out. 
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Post Fiend
Joined: Jun 2002
Posts: 13,873
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From: Atlanta GA
Heating up 86 BroncoII
With 196K miles the most likely candidate is the fan clutch. An electric fan might be a better option. Your motor and heads will last a long time if they do not overheat.
If you have an AT, a bad torque converter can overheat your engine.
I have a 1986 too, with a guessimate of 253k. With a new single core aluminum radiator, from NAPA, I do not even make it 1/2 way into the hot zone in GA heat.
If you have an AT, a bad torque converter can overheat your engine.
I have a 1986 too, with a guessimate of 253k. With a new single core aluminum radiator, from NAPA, I do not even make it 1/2 way into the hot zone in GA heat.
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