Overheating problem - '81 FJ40 (1 Viewer)

[mdwhiting]

Help appreciated in diagnosing my overheating problem. 1981 2F, RHD, has A/C but no heater. Serious overheating problem on drive home after purchasing a few months ago. There was fresh green coolant throughout system (pump and thermostat housing) but when I pulled radiator and flushed it - discolored. Also - there was no thermostat. Thought maybe air lock so flushed system. Flushed thoroughly - through block drain plug and from bottom of radiator. Burped system. STILL overheats, but is better than it was. Interesting though - turning on the A/C noticeably drops temps (almost a quarter of the gauge). Any thoughts - radiator problem? Temp sensor seems ok- checked with IR camera. My current 'fix' is no thermostat and running the A/C. Fan is 7-blade and a bit chipped but moves a lot of air.

 

[Grayscale]

Fresh radiator cap?

 

[3_puppies]

thermostat is a good idea with the top gasket
do you have a fan shroud?
you have a fixed fan, no fan clutch
have you used an inferred thermometer, to check actual temps? don't trust the gauge
bad water pump

 

[charliemeyer007]

AC load on the electrical system could make lower readings on the temp gauge, actual work done by AC should make it run hotter.

They likely pulled the thermostat because it ran hot. I would check the timing first retarded will run hot and so will a lean mixture.
Got a local shop - have the radiator rotted out. Make sure the fins are straight and clean. Use some chemical stuff to do the block.
Fan with good fitting shroud is important.

 

[hobbes]

You need a thermostat if you do not have one. It cycles the coolant at the proper rate to allow heat transfer. IOW, running no thermostat generally does NOT make your engine run cooler.

I'm not saying that will be the fix. But I'd start there.

 

[45Dougal]

Measure the electrical resistance of your temperature sender and confirm that it's correct for your year.
Check that the radiator cap is the correct pressure.
Check that your (aftermarket?)aircon isn't blocking the radiator airflow.
Perform an exhaust gas test in the coolant and check for head gasket failure.
Check that nobody removed the heater, and replaced it with a hose linking the two couplings on the engine and inadvertently bypassing your radiator.
More photos are always good

 

[cruisermatt]

x3 what are your actual coolant temps?

 

[mdwhiting]

thermostat is a good idea with the top gasket
do you have a fan shroud?
you have a fixed fan, no fan clutch
have you used an inferred thermometer, to check actual temps? don't trust the gauge
bad water pump

Yes, have shroud. I did check temperatures today after the drive home. I used a generic radiator cleaner, drove for about 20 minutes and checked temps. (no thermostat installed). Here's what I found (with engine/fan running):
Thermostat housing: 162 F
Upper radiator hose connection: 163 F
Lower radiator hose: 140 F
At these temperatures, the temp gauge was just a little right of vertical - not running hot. I find that if I am just driving around town at lower revs, no overheating issue. Any kind of sustained driving at 45 mph or more it is a problem.
I removed the upper radiator hose from where it enters the radiator to see how the water pump was working (while engine running - slowly and carefully.....) and a hose filling the radiator - the hot water came out in gushes (it wasn't regular, steady flow). It would come gushing out, then stop, then (about 5 s later) would repeat.....thoughts here? Maybe it was cavitating because I wasn't feeding water in fast enough? Or bad water pump? In my first photos you can see that PO patched it somehow.

 

[mdwhiting]

Measure the electrical resistance of your temperature sender and confirm that it's correct for your year.
Check that the radiator cap is the correct pressure.
Check that your (aftermarket?)aircon isn't blocking the radiator airflow.
Perform an exhaust gas test in the coolant and check for head gasket failure.
Check that nobody removed the heater, and replaced it with a hose linking the two couplings on the engine and inadvertently bypassing your radiator.
More photos are always good

Where is the temperature sending unit? Good thought to test that....
I did replace the radiator cap (13 psi - is that right?). Here's a photo - the AC doesn't appear to interfere with the radiator at all. I do wonder if the plate that it is mounted on places an excessive kink or restriction on the water pump?? Thoughts? Happy to send any photos that would help......

 

[mdwhiting]

You need a thermostat if you do not have one. It cycles the coolant at the proper rate to allow heat transfer. IOW, running no thermostat generally does NOT make your engine run cooler.

I'm not saying that will be the fix. But I'd start there.

My thinking was the same. I ran just water in the system for a while without thermostat and had the overheating problem. Put the thermostat (new) in and had a worse problem......

 

[mdwhiting]

AC load on the electrical system could make lower readings on the temp gauge, actual work done by AC should make it run hotter.

They likely pulled the thermostat because it ran hot. I would check the timing first retarded will run hot and so will a lean mixture.
Got a local shop - have the radiator rotted out. Make sure the fins are straight and clean. Use some chemical stuff to do the block.
Fan with good fitting shroud is important.

I thought exactly the same - the AC should make it run hotter. Visual inspection of radiator condition looks good - fins seem straight-ish and clean. I did try the chemical flush and it did help remove some rust/discoloration. Flushed that all out again today until it ran clear. Have the shroud - seems to be a good fit.

 

[hobbes]

The temperature sending unit is in the thermostat housing.

I believe it much match the gauge. That gets missed if the gauge or engine gets swapped for a different year.

 

[mdwhiting]

Just a couple of more photos.......appreciate all the advice!

 

[hobbes]

Typically the fan blades are somewhat exposed behind the shroud for best efficiency.

I believe Mark said direct drive fans move the most air.

My gauge stays left of center driving even in hot wx. Sounds like your gauge shows right of center even when not over heating if I’m reading your post correctly.

 

[mdwhiting]

The temperature sending unit is in the thermostat housing.

I believe it much match the gauge. That gets missed if the gauge or engine gets swapped for a different year.

Not sure where that would be? My thermostat housing has no electrical connections/sensors....what am I missing? This is pretty much what mine is:

 

[hobbes]

Maybe right here? In the parts files, it’s in the electrical section (switch relay computer)

 

[mdwhiting]

Typically the fan blades are somewhat exposed behind the shroud for best efficiency.

I believe Mark said direct drive fans move the most air.

My gauge stays left of center driving even in hot wx. Sounds like your gauge shows right of center even when not over heating if I’m reading your post correctly.

Ah - definitely no blades exposed beyond the shroud. Yes, the gauge is always right of center unless I am just puttering around town with the AC on! Any kind of sustained travel at 45 mph or more is a problem - gauge just keeps creeping to the right.....

 

[mdwhiting]

Maybe right here? In the parts files, it’s in the electrical section (switch relay computer)

View attachment 3734518

Oh shoot! I hadn't noticed that. Mine does not have that.

 

[hobbes]

You must have a sender somewhere. This is a 1981 general market diagram. Not sure your exact model so this might be off. But it looks like 2 sensor holes in the thermostat housing. If they are both plugged, then it’s been moved. Looks like it’s the same PN as the US models, 83420-20020. But I may have the wrong model.

 

[John McVicker]

I could be wrong on this, but from the pictures @mdwhiting posted he does not have the temp sender in the T Stat housing. I believe his temperature sending unit is on the right rear of the head in his picture in post 9.