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Mechanics Corner: Too much heat

Jim Schlund Published on 09 October 2010


Engines run on combustion. Combustion creates heat. Although heat is good for oil to work properly, some engines will get too hot and that causes problems.



The energy we want to use in an engine is combustion and the pressure that is caused by that combustion. Heat is just a byproduct. We hope that a big percentage of the heat goes out as exhaust. However, there is still conduction going on inside the cylinder and heat is absorbed in the parts and casing of the engine.

The heat then needs to be dissipated into the oil or the coolant. In turn, the oil cools through convection, while the coolant dissipates the heat into the air as the coolant runs through the little tubes in the radiator. As the air flows through the radiator, it pulls the heat out.

Coolant has special chemicals that aid in the transfer of heat and that’s why it’s important to use the right type of coolant – the blend that was intended for your machine – and change it when recommended by your manufacturer.

Heat that is absorbed in the metal parts themselves, like the casing and the block, through conduction, needs to be cooled. The air pulled in through the radiator and fans in front of the engine push the air through so the heat can be released into the air.

There are two laws in thermodynamics that are at work here: heat always travels to cold and the greater the difference between the two temperatures, the faster the heat moves.


That’s the science behind it, but let me tell you where the problem is. There are a few things owner/operators do that can hinder the heat transfer that needs to happen in their machines.

Dirty engines
If you are careless or neglect the outside of the engine, the oil and dirt and debris that collects on the outside of engine will act as an insulator for the engine. That not only removes one of the heat transfer processes, it also increases the workload for the oil and coolant.

Power wash
While cleaning the engine will help remove the dirt and oil that insulate the engine, exercise caution when using pressure washers. If you spray a radiator with lots of pressure, you can bend the fins of the radiator, thus decreasing the air flow that helps cool the engine and coolant. Also, high pressure on seals and caps can damage the seals and force dirt into the system.

Steam clean
When using really hot water to clean your engine, be sure you know how the parts will hold up. You can damage wires and sensors with steam. Use good judgement so you don’t do more damage to the engine than good.

I like to use warm water with moderate pressure. I still get the parts clean but I don’t damage the seals or force the dirt and grime into the system.

Mechanic’s tip
When your engine overheats make sure you pull over to safety, stop the engine, open the hood and wait for the engine and radiator to cool down enough so you can put your hand on it. Then you can put coolant back in. The reason why is there are differing thicknesses of metal in the engine and cooling system. If you immediately put cool liquid into the system, it will crack the metal because it cools too quickly. Having the engine off is important because it not only reduces the heat, but it also won’t pull the coolant directly into the hot parts of the engine, which would again crack the block or damage a gasket. PD

: If you are careless or neglect the outside of the engine, the oil and dirt and debris that collects on the outside of the engine will act as an insulator. Photo by Ryan Curtis.


Jim Schlund
  • Jim Schlund

  • Retired Diesel
  • Mechanics Professor
  • College of Southern Idaho
  • Email Jim Schlund