That darn yellow light is on again!!!

   / That darn yellow light is on again!!! #1  

dougfollett

Member
Joined
Aug 31, 2002
Messages
25
Location
Olympia, Washington.
Tractor
Yanmar 1500
It's me again with the Yanmar 1500 with the front loader. I was working around the homestead today trying to tidy up some areas that were kind of lumpy. Nothing real serious. I had already done most of the work the week before with the neighbors JD. I just wanted to smooth things out a bit so I droped the bucket and drug it backwards. I also scraped up several buckets of debri as well as pushed some piles aside. Nothing real strenious as far as I could tell. I did bog down a couple of times when I got in too deep with the bucket. After about half an hour I noticed the yellow light on the left side of the dash was on. I poped the hood and put my hand on the motor and radiator. It was hot but not smoking hot. I even dared to twist of the radiator cap (not smart) and it spit a bit but didn't boil out. Plenty of fresh green fluid inside. Front of radiator was clean. The round air filter does need replacing but other than that I'm not sure what is going on. Wire to the senor seems ok. Any ideas?
 
   / That darn yellow light is on again!!! #2  
Sensor could be going bad
 
   / That darn yellow light is on again!!! #3  
You are over reacting, that is the Japanese "time for a cold one light!"
 
   / That darn yellow light is on again!!!
  • Thread Starter
#4  
Could you be a bit more specific. If it were the heat sensor on my cars gasoline engin I would be very worried. Are you saying that it is different with diesels? I barely did any work with it. Is it typical for this motor to overheat that easily? I guess if it was serious they would have made it a red light and not a yellow one right?
 
   / That darn yellow light is on again!!! #5  
When I first got my 1500D it was doing the same thing. The problem was the anti-freeze mix. If the engine is overheating but the radiator is not too hot, I would suspect that you have too much antifreeze to water in the mix. If the mix isn't right, it won't circulate so the hot water isn't getting to the radiator to cool. The engine will be too hot and the radiator will still be cool or just warm to the touch.

To test for that problem, drain all your coolant into containers and then refill with water only. Then go work the tractor. if it doesn't overheat with water, the problem was the mix ratio.

The thermal siphon cooling system in the 1500 will not work if you have more than 40% anti freeze to 60% water.
 
   / That darn yellow light is on again!!! #6  
If I remember right I think He stated in his earlier posts that he was using a 50 50 mix. So if you are right that might be the problem.
 
   / That darn yellow light is on again!!!
  • Thread Starter
#7  
I think we're on to something. I drained about two quarts out and added water, then went out and did pretty much the same job I had done when it previously overheated. It overheated again. I then took a towl and lifted the cap off. About a quart of water\coolant blew out. It couldn't have been that hot because I wasn't scalded. It was hot though. I then put in another quart of just water, went back out and worked her again. This time I couldn't get the light to go on. I'm thinking it was pure coolant. How much liquid does the cooling system hold, any idea? Guess I need to drain it copleatly and go to a 60/40 mix like you suggested.
 
   / That darn yellow light is on again!!! #8  
or a 50/50 mix.
 
   / That darn yellow light is on again!!! #9  
I seem to remember that in past posts the experts have recomended less than 30/70 unless it gets very cold where you are. The correct mix does make a difference. You might want to read some of the old threads.

Chris
 
   / That darn yellow light is on again!!! #10  
Guys,
Here's the deal with the antifreeze mix and older Yanmar, and other Japanese tractors (including some of the older US Kubotas). The older tractors (including Doug's 1500) don't have water pumps to circulate the coolant. The system relies on the change in density of coolant as it changes in temperature. Basically, the engine heats the coolant, and the coolant becomes less dense (or lighter), thereby tending to rise upward. The highest spot in the system should be the radiator upper tank - this is where the hot coolant tries to go. The warmer, lighter coolant moving toward the radiator is replaced from below with cooler coolant in the bottom tank of the radiator. This circulation is referred to as the "thermo-syphon" effect.

Water has a relatively high coefficient of thermal expansion - that is to say it gets quite a bit lighter as it heats. Anti-freeze does not get much lighter when it heats. The thermo-syphon cooling system relies on a very clean system and a large change in coolant density to work properly. So the more anti-freeze in the mixture, the less the coolant circulates. For these cooling systems, you should use as little antifreeze as is necessary to prevent freezing in the winter. This provides the most effective cooling in summer.

I know this is a long post, but hopefully it explains the concept for those with thermosyphon cooling systems.
 

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