In the Red Zone

No, I am not talking about Football, I am talking about machines running hot.  The red zone for operating temp is never a good thing.  I take a fair amount of questions about cooling systems running "hot" or just under the red zone.  I will try to explain how the cooling systems operate and how we check them in our shop.

First off I should state that the electrical system on Toro equipment is designed to help identify an overheat situation.  This helps us by either shutting the machine down, (or in more recently built machines) shut the PTO system off first, then if the temp continues to rise, shut the machine down.  These systems are in place to save the engine from severe damage that can occur from an overheat situation.  I caution people to never disable this function.

So what do you do if your machine is overheating?  Virtually every time I see this issue it is related to one thing.  Not enough airflow through the radiator.  Either the fan is not spinning fast enough, or the radiator is plugged.  This is how we diagnose this-

1.Check the belt tension

We test the belt tension with a 13mm wrench and put it on a fan mounting bolt. We then try to turn it clockwise.  Can you turn the pulley with minimal force?  If so, the belt is too loose causing the fan to not spin fast enough.

2. Check the radiator for airflow blockage

Without proper airflow over the radiator the is no chance the cooling system will operate properly.  The easiest way to tell if you are getting airflow through the radiator is to check it with your hand.  when I perform this test I open the hood, move the oil cooler out of the way and place my hand next to the radiator.  *Do this when the machine is cold to insure the radiator is not to hot to touch!  Move your hand around the radiator.  Do you feel good flow through ALL areas of the radiator?  Too often the corners or the bottom third are plugged solid.  People blow out the center and feel they cleaned it, but they have missed portions.  The other biggest problem I see is people using water to clean radiators.  This will cause the bottom of the radiator to become completely plugged.  It creates a concrete like surface that can not be blown out with air once it drys.  We often have to completely remove the radiator to properly clean it at this point.

3. Check the Fan Clutch

The fan clutch determines how fast the fan will spin.  This is the aluminium piece that the fan is mounted to. There is fluid inside the clutch that stiffens up when the clutch warms up.  So when the machine is cold there should be little resistance in the fan clutch.  When warm, the fan should be harder to spin. If there is no change, the fan clutch is bad, and you are not spinning the fan fast enough.

*If the spring steel coil is missing from the front of the clutch, the clutch needs to be replaced 

3.1 The Direct Drive Kit (Toro #117-5665)

If your fan clutch is bad (or you do not feel you are getting enough airflow) there is a Direct Drive fan clutch replacement kit.  This kit was designed for machines with a cab & AC that put a heavier load on the engine.  This kit is a aluminium block that removes the clutch and bolts the fan right to the pulley.  There are some downsides to this approach though.  The increased fan speed will increase machine noise. (Hearing protection is recommended) You may also need more frequent radiator cleanings and may influence the fan belt life.

Check the seal of the rear screen

Once you have determined what the root cause of your overheating problem is, another thing to watch for is how your hood seals against the radiator when it is closed.  If there is not a proper seal, grass and other debris will plug the radiator much faster.  Look at the weather stripping around the rear screen, does it make a good seal?  If you have a 4500-D or a 4700-D the rear screen swings out of the way.  Over time this screen can get bent and may need to be adjusted to get a proper seal.


Of course there can be other factors the come into play with an overheating concern, but from my experience these are the most common causes.

Jim