Troubleshooting an Over-heating Engine

Chris Riley by Chris Riley Updated on August 7, 2019. In

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You have been offshore doing a little fishing, sitting stationary in a sargasso weed line. Both you and your fishing partner have noticed that each year it seems that more and more trash is accumulating in the weedlines. Styrofoam cups, plastic bags, and pieces of flotsam are strewn throughout. You have your limit of dolphin and can’t wait to get in and cook them “fresh off the boat.” The engine in your single inboard fires right up and off you go for the marina. Just a few minutes from your fishing location, you suddenly notice the temperature gauge is above normal and rising. What is your first course of action and how do you troubleshoot in the proper order to track down the problem in the shortest amount of time?

Many of you quickly diagnosed the probable problem as being a clogged through-hull intake. This may have been caused by sucking up trash, plastic or weeds as described in the questions’ scene. But what if that were not the problem? A special thanks to Bob Pone for providing information on how to remedy the worst case scenario, that of having a broken water pump. In order to trouble shoot an overheating engine you should:

  • Immediately shut down the engine.
  • Have your fishing partner keep sharp eye out for traffic.
  • Drift for a while to allow the debris that “could” be blocking the intake to float free while allowing the engine to cool. After the engine is cool you may have to go in reverse to dislodge the obstruction.
  • Meanwhile, you should open the engine room hatch and check the sea strainer.
  • Be sure to close the through-hull valve before taking the top off the strainer.
  • Once the wing nuts have been removed, take out the strainer basket and check for debris.
  • If there is no debris, gently “crack” the through hull valve to see if you have raw water flow from the outside coming into the strainer.
  • If you do not have water flow you know the intake is clogged.

Good news, the obstruction has floated free and you have water flow.

  • Put the sea strainer back together and be sure to open the valve.
  • Once the temp gauge reads in the safe range, start the engine and head home watching the temp gauge closely.

What if, however, you checked the water flow to the strainer, it was okay and the strainer was clean. What is next?

  • If you have water flow you know the problem is not a clogged intake.
  • Loosen the clamps and remove the hose where it enters the water pump. Open the seacock and check for water flow there.
  • If you don’t have flow, this hose is blocked. If you do you must go further.
  • Take the face off the water pump and check the impeller. The fins should be pliable and not cracked. If it appears worn, replace it with the spare that you “always carry.”
  • If the impeller appears to be in good shape it is most likely a problem with the water pump itself.

What to do with a broken water pump?

Contributed by Bob Pone

Your engine starts overheating, you go below and find that your raw water intake pump has become terminally ill and has stopped working. Panic sets in because the fish dinner you were dreaming about is as far away as your home port.

Not to worry! With a little imagination and some tools you will be on your way. Remove your galley’s electric pressure water pump or your electric bilge pump or any other electric pump that you can put into service and rig it between the raw water intake and your engine’s cooling system, bypassing the broken raw water intake pump.

This should get you to that fish dinner.


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