Yanmar Tractor Is Over Heating

My Yanmar Tractor Is Over Heating...... What Do I Do?

The Yanmar tractor cooling system is very simple but can still develop overheating problems. A little investigation & prevention can save you a lot of time and money.

be sure that you are using NO MORE than a % 25% antifreeze mixture in the summer (add more in the winter). These models use a very effective ThermoSiphon system and do not have a water pump. They use the natural tendency of hot water to rise to circulate the water. Too much antifreeze will not circulate correctly and does not conduct heat as efficiently. It sounds funny but Please Believe Us.... We get at least 2 or 3 of these calls per day! Dilute your mixture to 25% or less in the summer if your tractor does not have a water pump. Don't forget to add more antifreeze in the winter to avoid freezing.

Are you SURE it is overheating? If all of your water is "boiling" out of the radiator it could be a blown head gasket! Before you assume that it is overheating - check the water temp with a thermometer or mechanical temp gauge to be sure it is really too hot. A lot of "overheating" calls are actually "blown head gasket" calls. How to test- Let your tractor cool down completely. Fill radiator completely with water. Start engine with radiator cap off. If you see continuous bubbles in the radiator when the tractor is running then you probably have a blown head gasket. More info available by CLICKING HERE

Is the tractor really getting hot? The light is probably coming on but that may not mean that it is really getting hot. Temperature switches (the thing that turns the warning light on and off) do get weak. When they get weak they come on too soon. A $5 thermometer can be purchased at any automotive store. Placed into the water in the overflow bottle will tell you the temperature of the water and rule out any electrical problems. The light should come on around 220 degrees. If the thermometer shows around that temperature you will need to move to step 2. Otherwise you may need to replace your switch or look for other possible causes.

It is NORMAL for water to flow out of the radiator into the plastic bottle on the side. This does not necessarily mean that it is overheating. It does this because the water is heating up and expanding - it needs somewhere to go. Once the tractor cools, the water should be pulled back into the engine automatically. If the water is boiling out of the overflow bottle it is probably too hot or you have other issues.

Be sure that your radiator is clean on the OUTSIDE. If you have straw or tiny pieces of grass plugging up the fins then the air can not pull the heat out of the radiator and the engine will get hot. Even having a very small percentage of the radiator blocked can cause problems. Use compressed air to blow out the fins. Never use a pressure washer on a radiator. Also be sure that the outside fins are all open (not bent in or crushed) and the holes between the fins are all open & clear. They make a tiny comb to straighten the fins if you have some smashed spots. Check your local air conditioning supply shop.

Be sure that the radiator is clean on the INSIDE (flushed out). Keep in mind that just because you can put a hose in one end and the water shoots out the other does NOT mean that your radiator is working right. There are hundreds (just a guess.. I didn't count them) of tiny passages inside the radiator and the water may not be making it through enough of those to actually cool efficiently. Your tractor has 30 years worth of buildup in the radiator and it is likely causing a coolant restriction. You can run your hand along the front side of the radiator & see if you can feel spots that are noticeably cooler than other spots. This indicates that the coolant is not flowing through the radiator correctly. It may not be possible to flush the radiator if the buildup is severe enough. You may need to replace it.

Be sure that your belt is tight. The belt drives the water pump and the fan. If the belt slips your fan & water pump wont spin fast enough.

Check your hoses. Remove them & be sure the inner lining of the hose is still intact. A hoses inner lining can separate causing a bubble which can block the water flow.

Check your air filter. A clogged air filter will cause the tractor to work harder and possibly heat up faster.

Yanmar published a service bulletin in the 1980's in which they suggested owners of some models with overheating problems add foam rubber weatherstripping between the fan shroud and the radiator. The idea was that the fan was sucking air in through that gap in the sides instead of through the radiator. Be sure that 1- you HAVE a fan shroud and 2- that it is tight against the radiator.

If all of the above checkout- it might just be that you are working the tractor too hard. In the heat of the summer the tractor may not be able to perform at 100% for extended lengths of time. This is especially true when you factor in that the radiator is old and might not be working at 100% efficiency.

If you are unsure about any of these steps- please ask a qualified mechanic for help!