Operating temps

ghautz

Member
As I recall the conventional wisdom is that the maximum antifreeze mixture for a Yanmar thermosiphon cooling system is 70-30. That gives a freeze protection of 7 deg F, which is borderline for my area. Therefore I have been keeping mine at 50-50, especially for winter operation. The last year the engine temp has been up to 130 when mowing. When it started to exceed that regularly I figured I'd bite the bullet and replace the radiator (after a local radiator shop's repair quotes bracketed the cost of a new one). Because winter is approaching, I put in a 50-50 antifreeze mixture, with a dose of water wetter. The operating temp has been around 205 since then. I figure that is safe. For that matter, I figure 230 is safe since the OEM idiot light sensor trips at a reported 238 or thereabouts. Anyway, the question is: Will a weaker antifreeze mixture drop that temp significantly? I have heard reports that some of these engines run at less than 190.
 

Mark777

Member
ghautz,

Replacing the radiator on your 28 year young YM1500D is the single and biggest cooling performance upgrade you could make. Thermosiphon systems, or systems without a water pump, actually DO work much better with the 70/30 water-antifreeze mix, and the 190° temperature is a realistic figure during hot, summer operation. The 70/30 dilution ratio is the best scenario due to thinner viscosity and much better heat transfer for the convection designed cooling systems.

All that said, I would NOT hesitate to add plenty of antifreeze to keep from damaging the cooling system and engine from freezing winter temperatures.

Mark
 

Doc

Admin
Staff member
Gold Site Supporter
Synthetic oil will also lower your operating temp. I switched to synthetic in my boat (7.4L / 454cc). It cools by pulling water from the river. I was running at 160 with dino oil. After I switched I've consistently ran 5 degrees lower (155). All due to less friction.
 

ghautz

Member
Thanks for the reply, Mark. I'm inclined to leave mine at 50-50 and watch the temp gauge. If it tends to overheat during the summer I will dilute it.

Doc--changing to synthetic oil might double the value of the tractor.:) Sounds like a good idea if the cooling is marginal, tho.
 

California

Super Moderator
Staff member
Site Supporter
I was surprised how cool these things run.

I parked mine after pulling a loaded trailer a quarter mile uphill on plowed ground. (going backward - the hitch ball is on the loader!) That should have warmed it up since it sounded like it was working harder than during the backhoe work I had gone down there for. After I went in the house, I wondered if I should have allowed some cooldown time, idling before shutting it off.

So I went back out to investigate with my new $10 toy, a Harbor Freight non-contact thermometer.
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Not to worry. It measured only 165 degrees at the hose outlet on the top-front of the block. (at the sensor for the dash warning light.) 160 near the injectors, and only 150 on the block and at the top of the radiator. I used to work alongside a guy from Hong Kong who would have called this '10 second hot' - that's how long you can touch it before you have to pull away - so its easy to repeat this measurement later without fancy instruments. The crankcase and mid-radiator were 140, lower radiator 125, and the oil filter 120. I was surprised that the exhaust manifold was only about 200.

I normally run this thing about 1400 rpm for light loads, 1650 for moderate load such as this uphill towing, and seldom need to use the recommended full-power band of 1800-2400 rpm. Aside from discing and mowing that need the full output, I could have bought a smaller tractor for 90% of my projects.

This test seems to show it can cool fine at moderate load / lower rpm.
 

Doc

Admin
Staff member
Gold Site Supporter
:sorry: Didn't mean to cast aspersions at your boat, Doc. I type faster than I think, and I almost failed typing class. I figured that if the tractor still ran too hot I would consider using synthetic oil.

No problem. I didn't take it that way at all. Your original post about doubling the value made me chuckle for sure. :D
 
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