Interesting temperature readings on radiator

Hi all
So today I used my IR temperature reader on the FRONT of the radiator by going through the intake hole on the bonnet. The top of the radiator was 100-105 or so. As was the middle. But the bottom 4 or 5 inches was 145-150°. I was surprised by this and wondering if this might be an indication of a problem with the radiator. Clogging perhaps?

Also, I realize there is no fan shroud on the lower portion and wonder if I might want to add something to get the fan set to pull through the lower portion of the radiator

Was the engine running?

I’d call those readings suspect and recheck with the car at operating temperature and the engine running. Open the bonnet and be sure you are hitting the top and bottom tanks.

far too little information. Questions:

  1. What was the temperature on your gauge?
  2. Were the fans running?
  3. How long had the car been running?
  4. Was the top hose hot to the touch?
  5. Stock radiator or replacement?
  6. Condition of radiator?

This condition would be unsurprising if the thermostat wasn’t open yet, as there’s no circulation, but may still some migration through the open lower hose. The closed thermostat would tend to raise pressure in the block, which could force some coolant backwards through the radiator.

If the engine is warm and the fans are running, it may just be a peculiarity of measurement caused by airflow.

If the radiator is partially clogged, some tubes may never warm up fully.

On the question of the fan shroud, it’s always best to get airflow across the whole face of the radiator, but they did what they did and it would be tough to change. There’s no room for the big single fan of the S1’s, and with two 10" fans, you really can’t get full coverage. And it’s a down flow system, so the water at the top will be hotter than at the bottom anyway. The stock setup works just fine if everything is in good shape. But if I was going to do one mod, I would add a strip of sheet metal to the center of the shroud, to isolate the flow between the right and left fans.

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See above for replies. I’ve been running hot, see question 1 and have tried just about everything. Ready to pull the radiator and wondered if these temperature readings were an indicator


Did you see my answers to your questions?

Before you go to that trouble I’d take out the thermostat and test it in a pot of water on the stove.

From my limited experience I’d estimate the temperature to be between 200F and 212F for that needle position, assuming the gauge and sender aren’t wonky.

Fans on tell you the otter switch has closed it’s contacts which happens around 180F-190F. That’s assuming the otter switch is operating properly.

Perplexing is the apparent temperature of the upper hose and that you could squeeze it. The rubber hose doesn’t conduct heat as well as metal so it’s apparent temperature isn’t the best indicator of the cooling system temperature. Best to make sure you are getting a good reading of the temperature of the radiator where the hose enters the top tank.

A 68 might be different, but on my Series II the upper hose is pretty much unsqueezeable when the engine is at operating temperature. Are you sure the cap on the header tank is sealing?

I think Geo is right. First step is to pull the thermostat and check it’s operation

Thermostat, almost for sure. Even if the thermostat is closed, there’ probably enough leakage through the air bleed to trigger the fans. It’s certainly going to have to be checked, even if you do the radiator. So do it first.

My understanding is that 68 is the same as an S2 cooling system (S2 has the larger opening in the bonnet, but that’s the only difference)
My hose is definitely not firm at full temp.
There is no sign of leakage at either cap. Not really sure how to tell if it’s sealing…
Any suggestions?

I picked up a new thermostat housing, and have ordered a new thermostat. I was planning on doing that when I pulled the radiator, but I can do that first and perhaps save me the task of pulling the radiator.

Using the IR again, the top tank where the hose enters is about 205° and the bottom outlet is about 185°

That configuration sounds normal but the temperatures seem a bit high and the temperature drop from top to bottom possibly not enough (lots of other factors here including air movement).

Another exercise with the IR thermometer is to check various parts of the radiator to see if there are any spots that are cooler.

Don’t forget gaskets. I always order 2-3 for the otter switch, t-stat and other things that micht require more frequent removal and replacement.

On mine I built a rig with fittings, hoses a pressure gauge and valve that I plumb in line with the expansion tank. With the engine cold I can use the air compressor to put about 10-12 PSI into the system, close the valve and let it sit to see if the gauge drops or holds pressure. If it drops there is a leak somewhere.

I seem to recall reading that one way to test if the bypass isn’t being closed off is to put an external clamp on the hose between the thermostat and the water pump.
Is that correct?

The bypass is always overdiagnosed as a possible problem area. If the thermostat was wide open, you would have negligible flow through the bypass, even if the valve was completely gone or the casting lip was corroded. In fact, if you simply ordered a thermostat from any random parts store, you would likely get a single poppet thermostat rather than the correct item, and it would work reasonably well. You have a bad thermostat, period, don’t overthink this.

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Me? Overthink? Never! :roll_eyes:

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So… it doesn’t seem like it was the thermostat. I bought a new gates, and pulled the old one, and put them both in a pan of water and started to heat them. They both started opening at about the same time. They new one started out with the foot longer and it continued that advantage throughout the temp range.

I also installed the new housing, as the old one was corroded.

Put it all back together and while it seems better, the temp still is climbing past the L and approaching the red…

I’ve tested the system for leaks and when cold it holds 7 pounds.
Also tested for combustion fumes in the radiator and got a negative result.
Sounds like maybe it’s time to pull the radiator?
I’ve got new: hoses, 50/50 coolant, blades for the round fan motors, thermostat, thermostat housing, Water Wetter, swapped distributors to sure of timing and advance, and it seems it’s running a bit on the rich side to make sure I’m not running lean…

**Fans come on when they are supposed to, and never turn off as long as the car is running. The temp never seems to drop, only continues to climb. **

I’m out of ideas, and am tired of this problem that just won’t get better, regardless of how much time I put into it.

Did you try this as the radiator heated up?

There are several failure modes for a radiator including clogging and lack of good contact between the tubes and the fins.

Sometimes the mere weight of a removed radiator is enough to tell you it is full of sediment.