Model M John Deere, lower radiator hose cold?

psychonautbuddy · Apr 17, 2014

I am operating an old 1950 model "m", and after changing oil & other minor maintenance, I went out yesterday evening and cut brush for an hour.
Afterwards, before putting the JD to bed, I noticed that the lower radiator hose was cold?? I don't think the coolant is circulating! I took off
the cap, and the water/antifreeze could be seen at a level three or four inches below the cap.

As I understand, there is no pump or thermostat, so apart from a completely clogged radiator and or a very very efficient radiator, I'm at a loss as to WHY the coolant doesn't
appear to be circulating... There was no heat at the lower hose, is this normal?

RickB · Apr 17, 2014

If the coolant isn't above the level of the top hose connection, thermosyphon systems can't function. Make sure the radiator is properly filled.

psychonautbuddy · Apr 17, 2014

Yeah, I took the engine cover off and checked the fluid again, but that's as far as I got today. It didn't boil-over, so I guess it's just cold blooded.

pmsmechanic · Apr 17, 2014

I just looked in the parts diagrams and there is no thermostat. However there is an optional shudder for the radiator that closes the rad off via a manually operated cable. So a piece of burlap or plastic hung on the grill would do the same thing to bring up your engine temperature. You just have to learn to watch the temperature gauge.

RickB · Apr 18, 2014

M's are far more well known for running hot than cold. If you decide to cover the radiator (which I would not), make sure the temp gauge works, and keep an eye on it. There is no real benefit to artificially raising the operating temp of a gas engine.

pmsmechanic · Apr 18, 2014

There is no real benefit to artificially raising the operating temp of a gas engine.

I disagree with the above statement. There are benefits to running an engine at proper operating temperatures. The main one being that more of the gas gets burned completely which in turn means less unburnt fuel diluting the crankcase oil.

psychonautbuddy · Apr 18, 2014

Well, the ambient temperature was about 55f when I last operated. I have a digital thermometer; I will cut brush for an hour and sample the coolant temps just inside the cap to see if it's within range.
The lower hose is extra thick, two layers, maybe for abrasion resistance, so that could be why it felt cooler to the touch than say my automobile radiator hoses.

RickB · Apr 18, 2014

pmsmechanic said:
There is no real benefit to artificially raising the operating temp of a gas engine.

I disagree with the above statement. There are benefits to running an engine at proper operating temperatures. The main one being that more of the gas gets burned completely which in turn means less unburnt fuel diluting the crankcase oil.

We're discussing an underdesigned thermosyphon system here. One that typically is complained about due to overly high operating temps. If you had any direct knowledge of or experience with this particular system, just about the last bit of advise you would give is to cover all or part of the radiator.

psychonautbuddy · Apr 18, 2014

Alright, did a couple laps with brush hog, then I got out my digital multi meter, plugged in the thermometer, and got 212f sampling thru the radiator cap. I'm about a 50/50 mix.

I felt the lower hose, and the cast iron flange into the block, and it was barely above room temp. I popped off the sheet metal, felt accross the face of the radiator, hot at top,
warm in the middle, and so-so at the bottom of the fins. Putting my fingers on the lower tank, about room temp.

My guess is my radiator is clogged up! Funny though, it looked okay from the inside the cap.

If I get some positive feedback, I'll yank it and unsolder the bottom tank, rod it with an old dip-stick, and see what happens.

Whatcha say? Should this be in the part/repair forum?