# 641 Overheating



## mjewell (Apr 26, 2016)

Hello All:

First post. Just picked up a 1958 641. Test drove it and it did just fine, but it was a 10 minute check out run. Got it home and mowed a little bit (around 2 acres). Ran and did everything just fine, but the temperature slowly but steadily climbed to the top of the green arc. I shut it down and let it cool till the next day.

This morning I looked it over and started it up. Checked the radiator, found the fluid looking good. No water in the oil. Fan is turning fine, and it pulls good air through the radiator. Lower hose got warmer as the coolant warmed up. Let it idle, as well as drove it around a bit, and checked water temp and found it got up to around 170. Gage was headed toward the top of the green arc but never got all the way up. Never any hotter than 170 or so.

It looks like the thermostat is supposed to be 160. I think the thermostat is working because the coolant is getting warm like it should.

My questions: 1) The radiator cap doesn't have any pressure on it when I open it warm...should it? 2) Is it possible the water pump is not pumping as well as it should? 3) Could the lower radiator hose be plugged up?

Looking for advice. Been around engines all my life, so I know my way around. My thought is that the radiator could use a flush, and that the pump isn't working as well as it should. I think, too, that the thermostat is probably OK, it just isn't moving water through the system well enough to cool efficiently. Thoughts??

Thanks,

Mike


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## sixbales (May 18, 2011)

Howdy mjewell,

Welcome to the forum.

The temperature readings of 170 degrees that you posted seem quite normal, and should yield a gauge reading mid-scale on the green arch. Are you using an infrared thermometer to get these readings? This would suggest that your temperature gauge is inaccurate if it goes up to the end of the green arch. I guess that I would change the temperature gauge or temperature sending unit, or both. Clean the connections first to see if it improves. 

Your radiator cap should be a 4 psi cap. Very low pressure. 

One thing....Fords will not tolerate a full radiator. When they get warm they discharge coolant out the overflow till the coolant level stabilizes at about 1/2" above the cores. Perfectly normal...leave it that way.

A system flush shouldn't hurt anything. Make sure you flush out all of the chemical with water when done. Also, put some corrosion inhibitor in the coolant when you are done.

To check the pump, let it warm up good to open the thermostat, then remove the radiator cap and observe flow from the pump.

Does your radiator have a fan shroud? This is a very helpful item in your cooling system. Is the fan belt slipping?

Are you seeing any small bubbles in the coolant?


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## mjewell (Apr 26, 2016)

Thanks for the reply.

No bubbles in the coolant. As it idles I can see some movement in the water, but not what I am used to seeing in an older car. Also, I am using a dip-style thermometer that has always been accurate.

I do have a shroud on the radiator, and the belt seems tight, though I am going to replace it due to its' ragged looks. As for the cap, there is no pressure when I take it off hot. Perhaps I will replace it as well.


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## RM-MN (Sep 11, 2015)

That ragged belt could well be the problem. You may not notice it but they slip and the fan just doesn't move as much air. The belt on my Ford 3600 wasn't even ragged but a new one solved the overheating I was having.


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## mjewell (Apr 26, 2016)

I'm going to replace them both, and the radiator cap, tomorrow. I will report back with the results. 

Thanks for the replies.


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## TraderMark (Nov 15, 2011)

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Excuse the crude drawing above but it's the best I could do at the moment.
You should check the pulleys on the crankshaft and fan as well as the things mentioned.
The groove in the pulleys should look like the first drawing, a smooth consistent sloped V shape.
If the grooves are worn and look more like the second drawing you should replace the pulleys.
My skid steer would start to run warm so I replaced the fan belt. It worked great for a day or two then started to run warm again. I finally traced it back to worn pulleys on the fan and crankshaft. Replaced those two pulleys and was good to go.

HTH
Mark


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## mjewell (Apr 26, 2016)

UPDATE:

Drained the radiator and flushed it today. While warming it up, I noticed that, when cool, the water in the radiator was moving pretty swiftly, even at idle speed. Replaced the thermostat, and watched the water as it warmed up. Didn't move at all until the temperature gage got up to around half, then the water would flow and the gage would drop down. Got it good and warmed up, and went out and mowed a little with it, really loading it up to see if it would overheat. Temperature gage never went more than slightly above half, and the water temperature was 170. 

So, for now, I am proclaiming this one as resolved! I tested the old thermostat, just because that's the way I am, and found that it didn't function at all in 190 degree water. The valve (old style butterfly valve) was open a bit, maybe around 1/8" when I took it out, and never did anything as it heated up. My guess is that it was open enough to let the water flow (used to take a while to warm up), but didn't let it flow slow enough to cool it as it passed through the radiator, which led to eventually overheating.

Thanks again for the help!

Mike


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