Fj60 overheating when driving (1 Viewer)

[mnaser1994]

I have a 60 and I’m trying to tackle am overheating issue. It will only overheat after 5-10 min of driving. Never when idling

I have replaced the thermostat and radiator cap
Burped the system until no more bubbles came up
I ran a pressure test to 15psi and it does lose pressure but I’m not sure how to find out where it loses pressure from
The heat occasionally works well, other times it blows cold

any idea what to do? Thanks

 

[SteveH]

Do you know for sure that it's overheating? Have you aimed an IR thermometer (with the engine OFF to prevent engine fan wind) at the head when it's overheating? My head reads 201-205F at full operating temp, with the 188F t-stat (FJ62). Are both the upper and lower radiator hoses blazing hot when it's overheating?

If your heater is blowing cold air when the engine is overheating (and your heater valve is working correctly) something is whacked. I would do a compression test to check for a blown head gasket, and to give you peace of mind.

Many pressure test systems (that I have used) leak around the cap, so unless you have another leak, it may not tell you much. If you do a cooling system pressure test, and the engine misses when you start it, you may be pushing coolant into a cylinder, which is another indication of a head gasket issue.

Just some ideas here - others should chime in.

Steve

 

[Dr. John]

No coolant circulating to heater core could indicate water pump failure. With the rad cap off...look for a coolant level surge when revving engine. Engine must be warmed up enough to open the thermostat. As a firm believer in "cause and effect", was anything done to the engine just prior to this problem?

 

[ScottT]

This could also be a lean mixture problem. After 30 or 40 years there may be an accumulation of junk that blocks or partially blocks jets or air bleeds. This is not uncommon especially when using gas containing etoh.

 

[Seth S]

If you are going off the stock gage you need to verify it by other means. The IR gage @SteveH mentioned is a good way to go. Otherwise are you seeing coolant boiling out the radiator? It’s also possible you still have air in the system which is a common problem.

 

[cruisinAloha]

This could also be a lean mixture problem. After 30 or 40 years there may be an accumulation of junk that blocks or partially blocks jets or air bleeds. This is not uncommon especially when using gas containing etoh.

can you elaborate a little on how this ties into cooling?

 

[SteveH]

Lean engines run hotter than engines running with a proper air fuel mixture. They also tend to fry valves, and can spark-knock (suffer pre-ignition, technically).

 

[ScottT]

What SteveH said. One of the functions of fuel in an ice is to cool the engine. When there is not enough fuel to air the engine overheats potentially melting pistons etc. if there is gunk in the carb it can be sucked up into a jet causing a lean mixture condition. If it is only present at high demand situations it may drop back from gravity only to appear again at high demand situations.

 

[Seth S]

ICE = Internal Combustion Engine