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[Rob]

Last weekend I added about 1 gallon of coolant to my 1990 toyota
pickup. I decided to add coolant because the heat was not very warm
(just noticed with the colder weather) .
This week on the way to work the engine got very hot (very close to the
red on the gauge) As soon as I turned the heat off the engine went back
to normal.
I know most of the time if your engine is hot you are told to turn the
heat on to help with the cooling.... this is just the opposite.
Is my problem the thermostat ? or somethhing else?

[xblazinlv]

Did you add a gallon of water or anti-freeze. Anti-freeze is no
"coolant," water is coolant. The problem could very well be that you
added more anti-freeze than water and the engine isn't being
sufficiently cooled. You are correct though about turning the heater on
usually helping when the vehicle is overheating, that is a strange
problem.


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[Rob]

I did mix about 60 - 40 with water. Today I am going to top it off with the
engine running to make sure there is no air in the system.

[Mike Romain]

Running with pure coolant or too strong a mix will cause your engine to
overheat. I have seen that a lot.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
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[ase-tech]

overheating because of a strong coolant mix is not likely. the more likely problem is your vehicle over heated and lost coolant but went unnoticed till you lacked heat and investigated. more likely your problem is your thermostat.