Engine overheating

[ALEXGAR]

I did a search and could not find a suitable answer to my problem, so here goes:

I have a 1971 fj40 with an F engine. The engine is overheating and I can't find the problem. I have replaced the thermostat and tested the old one which still works. I also checked and tightened the fan belt.

The radiator is dumping water into the overflow reservoir (aftermarket), and when I stop and pull the radiator cap a "normal" coolant fizzes out (not even a teaspoon). I ran the engine in idle and placed a thermometer inside the filler neck of the radiator. It never went higher than 168 degrees. Meanwhile, the temperature gauge is over the third bar indicating overheating.

I could use some help! Many thanks!

 

[FJ40-GARAGE]

It never went higher than 168 degrees. Meanwhile, the temperature gauge is over the third bar indicating overheating.

I expect that your OEM gauge crapped out.

 

[numby]

Bad radiator cap. The spring in the cap has lost its tension allowing the radiator to overflow into the reservoir. Water boils easily at normal atmospheric pressure. The cap pressure makes it harder for boiling to occur.

 

[Southeast Overland]

Burp your system = free.

New radiator cap = cheap.

New OEM temp sender = little more $.

All should be easy. I might even have a temp sender if a 2f sender will work.

 

[inkpot]

Howdy! Sounds like you have some blockage in the system if the hot water isn't making it to the radiator. Check for a buckled lower hose. Could even be a thermostadt put in backwards. It's pretty rare, but I have seen the impellers on the water pump corode away to nearly nothing, so the don't move any water. John

 

[MtnClimber]

Not to mention the impellers can be bent if run with partially/totally frozen coolant. If they are bent, a new pump is in the works.

It sounds like there is no movement of coolant. Replace water pump, replace rad cap just for measures, and make sure the overflow is the type where the dump tube is submerged at all times.

 

[Southeast Overland]

Alex, are you wrenching today? Shoot me a text, email or PM. I don't have any plans for today besides beer and wrenching.

 

[ALEXGAR]

Bad radiator cap. The spring in the cap has lost its tension allowing the radiator to overflow into the reservoir. Water boils easily at normal atmospheric pressure. The cap pressure makes it harder for boiling to occur.

Thanks! I thought the same thing and replaced the cap. Still overheating.

 

[ALEXGAR]

Alex, are you wrenching today? Shoot me a text, email or PM. I don't have any plans for today besides beer and wrenching.

PM sent

 

[Thornton]

Just read your thread and sounds like your having the same issues I've been having. My '71 F always ran at the second mark on the guage for the past 4 yrs. While doing power steering I went ahead and installed a new water pump and hoses, also installed a 2nd valve to completely shut off the loop to the heater. That worked great keeping the cab cooler but the guage went up some more and on the trails it would run all the way up when idling. Next I changed the radiator with one that I had ordered for the '73 I'm working on and ordered a 6 blade plastic fan and t-stat. This brought it down a little, just below the 2nd mark on the guage. Here's why I really feel stupid over the whole deal. After I installed the new water pump I also got a new sending unit and guage, one point I thought Ihad fried the guage. I finally went out today and installed the new sending unit. After going out for about 45min. in 90 deg temp the needle on the temp guage went it's own width past the 1st mark. I should have tried the sending unit earlier. FYI the part # is 83420-20010

 

[Brian in Oregon]

A leaky head gasket can cause exhaust gas to be forced into the cooling system. This can raise pressure to beyond what even a brand new cap can hold. It appears to be overheating because the cap can vent, as noted by the coolant going into the overflow. There are pressure checking tools that replace the radiator cap that can tell you what the system pressure is. This particular problem is very difficult to diagnose without the pressure gauge tool.

 

[82HJ47]

I recently fitted an auxiliary VDO temp gauge on my '77 FJ40 as I don't trust the OEM ones. Word of caution if anyone is thinking of going this route, the OEM sender needs to be swapped out for one that's compatible with the new gauge.

Discovered immediately I was running VERY hot. Had already flushed the cooling system prior to fitting the new gauge as a general maintenance measure so was now left wondering what my problem was......took the radiator in and they opened it up to do a flow test, it was about 53% blocked [85 out of the 160 tubes], I saw it with my own eyes! There was my problem right there. Replaced the radiator with a new one [same price as a re-core on my original], fitted a new OEM 82 deg C thermo with the rubber sealing ring, new hoses, fresh coolant, new OEM cap and I'm now sitting at 82 deg C [180 deg F] no matter how hard I drive her....problem solved.

So, despite having flushed the rad, and water seemingly flowing through it beautifully with the hosepipe in the top flushing clean water through it was actually over 50% blocked and the cause of my problem, so Alex, something to bear in mind.

I think I can attribute this to the vehicle having been laid up in a shed for close on 20 years and only recently being re-commissioned.

 

[ALEXGAR]

Found the problem(s)!

It's the sending unit OR the gauge. Trollhole came over and we inserted a digital temp guage into the top rad hose. We fired-up the 40 and let it idle for several minutes.

While my OEM gauge showed operating temperature, the digital showed roughly 130 degrees. When the digital rose to normal temp (180), my OEM gauge showed the needle half way between the third and last line.

Despite accelerating the idle, the digital temp remained at 180 degrees, the OEM crept upward.

Many thanks to all of you for pointing me in the right direction!

A leaky head gasket can cause exhaust gas to be forced into the cooling system. This can raise pressure to beyond what even a brand new cap can hold. It appears to be overheating because the cap can vent, as noted by the coolant going into the overflow. There are pressure checking tools that replace the radiator cap that can tell you what the system pressure is. This particular problem is very difficult to diagnose without the pressure gauge tool.

I recently fitted an auxiliary VDO temp gauge on my '77 FJ40 as I don't trust the OEM ones. Word of caution if anyone is thinking of going this route, the OEM sender needs to be swapped out for one that's compatible with the new gauge.

Discovered immediately I was running VERY hot. Had already flushed the cooling system prior to fitting the new gauge as a general maintenance measure so was now left wondering what my problem was......took the radiator in and they opened it up to do a flow test, it was about 53% blocked [85 out of the 160 tubes], I saw it with my own eyes! There was my problem right there. Replaced the radiator with a new one [same price as a re-core on my original], fitted a new OEM 82 deg C thermo with the rubber sealing ring, new hoses, fresh coolant, new OEM cap and I'm now sitting at 82 deg C [180 deg F] no matter how hard I drive her....problem solved.

So, despite having flushed the rad, and water seemingly flowing through it beautifully with the hosepipe in the top flushing clean water through it was actually over 50% blocked and the cause of my problem, so Alex, something to bear in mind.

I think I can attribute this to the vehicle having been laid up in a shed for close on 20 years and only recently being re-commissioned.

 

[numby]

So what caused the boil over? Head gasket or?

 

[ALEXGAR]

So what caused the boil over? Head gasket or?

There was No boil-over. My temp gauge was incorrectly showing overheating.

I'll be getting my new OEM sending unit from the good folks at Ralph Hayes Toyota.

 

[numby]

The radiator is dumping water into the overflow reservoir (aftermarket), and when I stop and pull the radiator cap a "normal" coolant fizzes out (not even a teaspoon).

Sorry - I guess I didn't quite understand the first post. Glad you've got it all squared away.