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Prevent Heat Soak to Prolong Life


Everything on a farm works hard, and an engine is no exception. Regardless if it is gas or diesel in a tractor, sprayer, or pickup, one fact remains: The conversion of chemical-to-mechanical energy produces heat. Each gallon of fuel has a heating value measured in British thermal units (Btu’s). Thus, the thermal load is intrinsically linked to the rate of fuel consumption. 

This is not to be confused with the temperature gauge reading, which is the heat absorbed by the liquid coolant. Under high load, the liquid temperature may not change much or at all. The rest of the engine, and especially the exhaust temperature, goes up substantially. This raises the under-hood temperature. 

On newer diesels, this is exacerbated by the lack of under-hood air movement and other factors such as EGR, turbocharging, and an air-conditioning  system. Elevated under-hood temperature is the silent killer of engines and their components. 

Under-hood temperature rises dramatically when the engine is shut down. This is due to the mass of the engine having a high thermal capacity. 

It is known as heat soak and is defined as the excursion in temperature after the engine is shut off. 

Heat Kills Parts 

Heat is the enemy of everything under the hood and results is a shorter service life. Rubber hoses and belts, engine gaskets, wires, sensors, electronics, seals, alternator, battery, radiator, the emissions system, and air-conditioning components are all degraded during heat soak. Even the engine block, cylinder head, and turbocharger are impacted.

The good news is that it’s quite simple to reduce this effect. Simply idle the engine for one minute before shutting it down and then open the hood. 

Letting the engine run for just one minute will allow the cooling system to work and limit the thermal excursion.

Since heat rises, opening the hood will allow it to travel into the atmosphere instead of being absorbed. When you are done for the day or are stopping work for some reason, just open the hood and let the heat escape. It may take a sticky note on the dashboard to get you into the habit, but this little effort will pay huge dividends over time. 

Be prepared to enjoy longer gasket, hose, electronics, and belt life, and not have all the connections and wires become brittle. It will make the difference between a simple task turning into a nightmare because a connection broke when you touched it. 

Today’s farm equipment has an engine compartment that creates heat soak. If you want any engine and its systems to last longer, open the hood and let the heat out!


The Engine Answerman

Ray Bohacz has engine grease and field dirt under his fingernails from a life spent repairing vehicles and running a farm in New Jersey with his wife, Charlotte. His how-to articles also appear in Diesel Power, Engine  Professional, Hemmings Motor News, and Speedway Illustrated magazines. Contact Bohacz via email at


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