Re: Thermostats

Interesting post on thermostats. My Md never gets out of the "cold" zone even when plowing for 6-7 hours in May 55-60 degrees. I know about restricting the bypass but didn't want to risk cracking the head. I'm paranoid about proper warmup and cool down on this thing. It seems like shutters would be the answer, but I've never been able to find one for an MD.

Head cracking on a Gas start Diesel Run IH is not caused by running them at temperature. It is most often caused by rapid changes in head temperature.
Not warming them up from cold for 5 minutes or so before going to full power, or getting them good and warmed up from field work and shutting them off like a light switch. (also should take 5 minutes of near idle/idle running)
I believe (and was successful with mine) that they cool off more uniformly when idled on diesel than switching to gas, as a idling diesel makes much less heat than a gas burner, and the quick reheating of the spark/compression release chamber running on gas would seem to me to build more temperature change into the head and starting valves just before shutdown than running on diesel. (I have read the manual) Jim

Thanks for comments, Jim, which are always valued. So far, I've gone by the book on shutdown...I let the tractor idle on diesel for 10-12 minutes but have switched back to gas before shutting off without issues. I suppose the book says to shut down on gas for easier starting next time. If shut down on diesel, how hard is the tractor to start after an hour or so. I've always believed in "going by the book" but I see your point on the cooling aspect.

The starting valves should be closed (diesel mode) after shutdown in either case. The reason being that the valves when open are hanging in the combustion chamber with no edge support, and no cooling touch to the seat. I believe that leaving them closed provides less heating of the starting valves in the first place.
The head castings are complex. The saturation heating from real work/load is as uniform as it can be through the mass of the casting. I see no concrete reason to "cool" it by using gasoline combustion exposing more surface area to heat. (I ride diesel busses every day to work. They have diesel powered heaters that provide cabin heat for passengers because the busses are not worked hard enough to provide engine heat to the heater cores)
Jim

its a diesel engine, and I have always shut down on diesel. a diesel engine at idle produces less heat than a gas and cools lots faster on diesel. diesel shut down has no effect on the gas restart at all. many people say they switch to gas to clean the plugs for the next start. well this is totally not true as the diesel combustion never see's the plugs. proper warm up and cool down is the biggest factor as in any engine. other than the jimmies ... as they are 2 cycle and not as particular. say when power goes down in a hospital they can have the jimmie back up power running wide open quickly.
I have always thought to myself that whoever wrote the manual did not totally understand diesel operation back then.
also on the WD40 it is gas start also and CANNOT be switched back to gas once it is running.

Thanks, I will try this as soon as I have it up and running again. Head is off right now. The diesel shutdown totally makes sense and easier since lever is already in diesel position. I have never dared to question manuals (lol) but maybe its time to start.

Gas start diesels have served on our farm for 61 years and we still find uses for them today. We have never shut down on gas and they start just fine. I completely agree that proper warming up and cooling down is paramount. We have cracked 3 heads. The first one was cracked by by my brother starting the tractor in the spring and not realizing that the water had been drained in the fall. He started adding water and of course that cracked the head. The other two heads were cracked by incorrect timing of the injection pump on one tractor. At some point in time the timing had been adjusted to make the tractor switch over to diesel effortlessly and run very smooth at idle when cold. This causes the engine to run warmer than normal, even at idle. In the field, the tractor ran fine and the temperature gauge would easily get to the normal zone (which is not normal). This resulted in two cracked heads before the problem was discovered.

I recall another member's comments about the manual stating that the engine should be shut down on gas. That member suggested a very good point which was when these tractors were first sold some of them may not have had electric starting so the hand crank was the only option. Shutting down the engine on gas may have helped starting with the crank by having some gas pass through the system at shut down. This is basically a non-issue with electric starting. It was a good comment by that member, whoever it was.

Take a bunch of testing with heat sensors added to the heads to know for sure what's the coolest shut down. I don't know the answer.
Can only say out of 11 MD to 450 tractors I owned in my lifetime. Only one still was equipped with the original head and according to the previous owner it was always switched back to gas before shut down.
Kind of think there may be more causes to the cracking other than what fuel they were shut off on. Many claim one or the other is how they done it with good luck. Also many from both ways claim problems.
All I can claim is if you work one hard and have the temp. up and kill the engine its best to have gas in it and a good starting system to quickly get it running again.

(quoted from post at 15:45:06 02/09/14) Interesting post on thermostats. My Md never gets out of the "cold" zone even when plowing for 6-7 hours in May 55-60 degrees. I know about restricting the bypass but didn't want to risk cracking the head. I'm paranoid about proper warmup and cool down on this thing. It seems like shutters would be the answer, but I've never been able to find one for an MD.

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One thought about putting shutters on a gas start diesel. With shutters, it is very easy to forget that you have left them closed or perhaps closed a little too much resulting in overheating the engine which most of us can agree that overheating a gas start diesel will likely result in a cracked head. Instead of shutters, I prefer a piece of cardboard or plastic on the outside of the grille in cold weather. It is a much better visual reminder that the radiator is covered and I adjust it accordingly for the weather as required.

Just a few more comments to go along what you said. I bought a used MD in about 1966 with about 3500 hrs. It now has about 7200. The head has never been off in the 45+ years I have had it. Never pulled it hard when it was cold and never shut it down when hot. I put a new temperature gauge with numbers on when I got it. After it warms up it will idle at about 140 in 50 degree plus weather. So the thermostat must still be working. I also have a 650-D that also idles at about 1/2 way up on the cold mark. So I think the gas-start diesels should show some heat on the gauge at idle after they have been warmed up. When we used the MD for farming, I always let it idle down on diesel to about 140 before stopping it. But I always switched it gas for a few seconds before shutting off the switch. Then always pulled the lever back to diesel to close the starting valves. Anyhow, just wanted to say the gas-start diesels will run a long time it you take care of them. Al

Are you sure the engine is not coming up to temperature. I discovered that my MD was coming up to temperature, but the temperature gauge was bad. I put a thermocouple in the radiator and found it was at temperature when the gauge said it was still cold. Roger

Thanks. The gauge is new but that doesn,t mean much these days.

actually its not a major issue since the tractor is never used in winter. I'll just be sure the thermostat is working.

Thanks. I do the same with mine. The temp gauge registers about in the middle of cold when at the temps you mentioned, but never gets quite to run range even when working.