Anpther FJ 60 Overheating question

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Apr 26, 2008
Hi I am new to this forum:

I own a 1984 FJ 60 with 200,000 and have had a heck of a time trying to figure out the cause of the OH(overheating) . Specifically, the truck runs at normal temp when driving around town and on the highway in cooler temps. Running on the highway in very hot temp causes the gage to go to 3/4 mark especailly after long rides. (two hours). The problem though is after running on a highway and then stopping like in traffic or at the exit offramp my guage climbs to the very top near the red zone. I have to put the heater on to pull the heat off. I also noticed that if i keep the engine revved, the temp gage drops down. The mech checked my block-no cracks, temp at idle is normal, cored the radiator, new water pump(aftermarket pump). He took out the thermostat?(should this be out) fan clutch is supposedly ok? Pressure tested system and is ok. Hoses fairly new? I also noticed water running under the dash after turning on the heater. Does anyone know what this good be?

Thanks for your advise
1984 FG 60 4in lift
lowered gears 4.92

If the problem occured after you changed hoses or replaced the coolant you could have air in your system. The high point of the system is near where the temperature sensor is and the air collects there and can give you an abnormally high reading. Do a search for "burp" in the 60's forum.

It could also be your fan clutch. It's a silicone oil clutch for the radiator fan that engages when the engine bay gets hot enough. If it's working, you can hear it kick in at the higher RPMs (I hear mine when I'm on the freeway on a hot day cycling on and off). At highway speeds you get a lot of air flow without the fan engaged, but not when you are stopped in traffic with residual heat to dissipate. That's when you need the fan clutch to work.
I would buy a new T-stat & install it yourself (very simple- 10 min. tops) be certain to ask for the rubber 'O' ring that sits on top of the T-stat. It's an important part that is often overlooked.

Try to mechanically lock up your fan clutch (I used a piece of rope) and see what the effect is.
Whoa, water running under the dash? Pure water or with coolant? Does your truck have A/C and were you using it at the time?

If your truck is leaking coolant into the truck, you must have it repaired before going after the heating problem. They may be related anyway.

A coolant leak in the heater core, hoses or valve can introduce air into the cooling system. Engine damage can result.

x2 on the thermostat. It sounds like the heat of the engine is not being conducted out through the cooling system. The thermostat is a REGULATOR of water flow. If the coolant is allowed to pass unrestricted through the engine, it flows too fast and cannot absorb the engine heat.

I would verify the claim that the fan clutch works. Your fan clutch should be locked after your freeway drive and the temp is high. Is that the case?

Please keep us informed of your findings,

X3 on t-stat...there's a reason it's in the cooling system to begin with :)

My other recommendation from dealing with similar issues myself is to get some actual temperature measurements on the cooling system. Install a mechanical gauge in place of the stock sender or check the temps with an infrared unit when you think the truck is close to the "red".


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