Question: The temperature gauge for my engine is reading higher than normal. One of my boating buddies told me that all I need to do to correct this problem is remove the engine thermostat. Is this a good idea?


Removing this outboard's thermostat may actually cause the engine to run hotter.

Answer: No! It’s a really bad idea. In fact, by removing the thermostat, the engine may actually run hotter.

Your engine’s thermostat is designed to keep your engine running at the hottest temperature it can without causing any damage. This in effect increases the engine’s thermal efficiency, which translated into plain English, means better fuel economy. At today’s prices, that’s a big deal. On the flip side, engines that run cooler than they should will tend to gum up inside over the long haul.

The thermostat actually acts as a controlled flow restrictor inside your engine’s cooling system. This is important, as the reduction in flow actually allows the cooling water enough time to absorb the heat generated and conducted through the metal parts of the engine. Without the restriction, the coolant will move too fast through the system and not allow enough time for effective heat transfer from the metal to the cooling water and ultimately out through the engine’s exhaust.

The best way to test your engine’s thermostat for proper operation is to remove it and set it in a pot of water on a stove top. Place an oven thermometer in the water and slowly heat the water while closely watching the thermostat to see when in begins to open. Observe the temperature at which this event occurs.

Based on the picture you sent your engine is an outboard, which means it is seawater-cooled. (Most modern inboard type engines have a closed cooling system.) Raw water cooled engines must be temperature regulated to a maximum of 160° F. This is very important because at approximately 165°F the salt from the seawater will begin to crystallize, wreaking total havoc on the inside of your engine through corrosion, plugged cooling passages, and so forth.

So, do NOT remove your engine’s thermostat as your buddy suggests. First determine for sure that the engine is actually running hotter, and not just having an issue with the temperature gauge. If it is actually running too hot, then further investigation will be needed. Let us know what you find, and we can discuss the next step.

—Ed Sherman