Overheat help! (5 Viewers)

[BiminiTwist]

Hello all,

To preface, I’m not a mechanic. I can however read and have not been able to find a solution (neither has a shop). I have a 78’ FJ40 with a 76 2F motor. I have had it for about 4 years and have maybe put 100 miles on it. Odometer says 3300 after the rebuild that I didn’t do. Shortly after I got it, it started overheating and I am out of ideas for how to fix it. I have replaced thermostat, replaced the radiator, water pump is good and flushed it multiple times.

It has an electric fan that I reinstalled after the previous owner took it off. I don’t know what else to do any help would be greatly appreciated.

Some side information, anytime I turn on an electrical component I.e. heater or fan, the temp with will immediately go up 10 degrees with every electrical item turned on. I know the gauge isn’t accurate in that case and when I shoot the block with a temp gauge I’ve gotten up to 450 degrees.

I would really like to get this done myself but I would also really like to be driving it…

 

[brian]

Hello all,

To preface, I’m not a mechanic. I can however read and have not been able to find a solution (neither has a shop). I have a 78’ FJ40 with a 76 2F motor. I have had it for about 4 years and have maybe put 100 miles on it. Odometer says 3300 after the rebuild that I didn’t do. Shortly after I got it, it started overheating and I am out of ideas for how to fix it. I have replaced thermostat, replaced the radiator, water pump is good and flushed it multiple times.

It has an electric fan that I reinstalled after the previous owner took it off. I don’t know what else to do any help would be greatly appreciated.

Some side information, anytime I turn on an electrical component I.e. heater or fan, the temp with will immediately go up 10 degrees with every electrical item turned on. I know the gauge isn’t accurate in that case and when I shoot the block with a temp gauge I’ve gotten up to 450 degrees.

I would really like to get this done myself but I would also really like to be driving it…

450F?

 

[Pighead]

Are you using the temp sender that came in the '76 block? With your '78 gauge?
Hook up a real water temp gauge before you panic.

 

[charliemeyer007]

IR laser thermometer are cheap. Sample the block and head plus the radiator in many places. Park on a steep ramp - take cap off and run long enough to burp the system, by seeing the surge as the thermostat cycles. If you have two heaters, put a big hemostat on one supply hose for a while then the other one. How does it run, retarded timing will make it run hot. Bad brake booster leaking can may it run hot - look at #5 spark plug. Maybe they bored it way out and the cylinder walls are too thin.
Fan turning the wrong way - might be trying to push air forward. Direct wire it so it stays on and see if that helps any.

You are running 50/50 mix, 100% ethylene glycol will run hot

 

[Rocky_LC]

It can’t be 450*.

All good suggestions (above).

The dollar bill trick (put a dollar bill on the front of the radiator to prove the fan is sucking) is a good test.

Does it puke out fluid when you stop with a full radiator? Does it make boiling sounds?

Rocky

 

[BiminiTwist]

Are you using the temp sender that came in the '76 block? With your '78 gauge?
Hook up a real water temp gauge before you panic.

It is an aftermarket gauge cluster, I don’t think it is stock to either year.

 

[BiminiTwist]

It can’t be 450*.

All good suggestions (above).

The dollar bill trick (put a dollar bill on the front of the radiator to prove the fan is sucking) is a good test.

Does it puke out fluid when you stop with a full radiator? Does it make boiling sounds?

Rocky

I didn’t think so either, I’ll try and get a pic next time. Fan is spinning the right way, and yes when it’s topped off it will dump out fluid for a while. Doesn’t sound like it’s boiling though.

 

[Mr. Green]

So electric fan, does it have mechanical fan too or just electric?
Likely you have air in it yet too not burped out… unsure if you got thermostat installed correctly OEM or aftermarket but gasket can be misleading.

 

[John McVicker]

On these engines a mechanical fan will cool MUCH better than an electric fan. MUCH BETER.

Get an IR gun to determine what your actual temperature is. Then decide if you need a new radiator (if so, get a good one) and/or if all you need is a proper burping of the system.

Are you using a fan shroud? Etc. etc.

 

[charliemeyer007]

I have a big rear heater so my coolant capacity is near 4 gallons. If I fill the system to cap cold it will puke fluid out the rad cap when it gets warm to operating temp. My overflow system is weak, and it doesn't get sucked back into the radiator. Any way when it cools down, the radiator will be down a little. However it will stay at that level for years and never pukes any more coolant.

 

[JohnnyC]

I second that it’s the electric fan

Pic of the fan setup?

 

[Skreddy]

At 450 degrees your coolant WILL be boiling out the overflow and you WILL have a cracked head and you’d probably already have burst the rubber coolant lines. Whatever you are using to check that temp is wrong.

I would bet you aren’t overheating at all, if all you’re relying on is the in dash gauge. Probably a mismatched sender and gauge?

But, I agree to ditch the electric fan and go back to stock type.

If you fill the radiator all the way to the top, it will spit coolant out. They need a little room for expansion so let it puke and don’t top
It off, it’ll tell you it’s happy level.

 

[BiminiTwist]

On these engines a mechanical fan will cool MUCH better than an electric fan. MUCH BETER.

Get an IR gun to determine what your actual temperature is. Then decide if you need a new radiator (if so, get a good one) and/or if all you need is a proper burping of the system.

Are you using a fan shroud? Etc. etc.

I did try to reinstall the mechanical fan but I just couldn’t get it to fit. When through 4 sets of bolts… the fan does have a shroud and the 450 came from an IR gun on the block.

 

[BiminiTwist]

At 450 degrees your coolant WILL be boiling out the overflow and you WILL have a cracked head and you’d probably already have burst the rubber coolant lines. Whatever you are using to check that temp is wrong.

I would bet you aren’t overheating at all, if all you’re relying on is the in dash gauge. Probably a mismatched sender and gauge?

But, I agree to ditch the electric fan and go back to stock type.

If you fill the radiator all the way to the top, it will spit coolant out. They need a little room for expansion so let it puke and don’t top
It off, it’ll tell you it’s happy level.

That’s what I was leaning towards also but it’s a little nerve wracking watching the temp gauge climb over 250

 

[BiminiTwist]

I second that it’s the electric fan

Pic of the fan setup?

 

[charliemeyer007]

450 on the exhaust manifold/header is reasonable. Maybe the holes were striped in the pump and someone re-tapped to SAE. Go to like Home Despot or Ace hardware and buy 1 bolt and nut in the sizes close to the size of the pump holes in both fine and course thread pitch. Ex 1.5" or 40mm long 1/4"-20 and 1/4 -28; 6mm - 1.0; 5/16" in 18 and 24 tpi, 7mm 1.0; 3/8 in 16 and 24, 8mm in 1.0 and 1.25; 7/16 in 14 and 20; 10mm in 1.5 and 1.25.

test the holes and see what fits

 

[John McVicker]

I did try to reinstall the mechanical fan but I just couldn’t get it to fit. When through 4 sets of bolts… the fan does have a shroud and the 450 came from an IR gun on the block.

A) get your IR gun on the radiator & the hoses going to/from the radiator. This is the best way to determine if you actually have a problem or not. And the temps you see will give you correct information as to what to do to solve the issue…OR…if you have an issue or don’t. Otherwise you are guessing & getting nowhere.

B) W/O being there with you it’s difficult to determine why you can’t get a mechanical fan on there…BUT…somehow get it figured out and REMOVE the electric fan. You will not solve your issue with your 2f until you do.

 

[Mr. Green]

In a pinch you could buy a flex a lite fan and adapter. Can make really short without a shroud and it moves mountains of air. That was my old setup.

 

[anothernz45]

Looks like the adapter holding your electric fan blocks off a lot of the radiator core, remove all that for a start. Your hand is a good IF thermometer, put it on the radiator top tank then bottom, should be noticeable difference if thermostat is working - always use a genuine one. X4 for refitting original fan

 

[bhsdriller]

Get something similar to this and see what your actual temps are

https://www.amazon.com/Dorman-7-123-Water-Temperature-Gauge/dp/B002ET4O5C/ref=sr_1_9?crid=3USO9GA2N0KU&dib=eyJ2IjoiMSJ9.DFqc963JO5rqiBR8n-VyKyL6NIjcDgrvG2ISzireBrMMuXr_ijgw2VI38biAsjg9u2b-4JPuoK7PHMdNVzyRsC6rRknCNmORp9tLx-7BgrfKh50WCbfb_U2Okttth96BIW1AlxZsIedb8pDQcO4TOyZE9b7yc2_F_xIeajNimJzhZSix0PIncizQDIum3yk9cnV9B32ojj3BUI9qMIpUbD9h8p0XN421Be6liHDn6ZQ.Mt1eNuam4AVYU7q0ggOpXGM2bXLD8jUBdeWLbc4Tc-I&dib_tag=se&keywords=water+temperature+gauge&qid=1749584746&sprefix=water+temp%2Caps%2C168&sr=8-9