How to find water/air leaks in cooling system
05-04-2021 | 02:35 PM
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How to find water/air leaks in cooling system
Since @boater24178 asked...
I don't take credit for the original idea. Dodge on another forum I think told me about it.
This engine would start and run 'fine', but the temp would go up, then down, then up, then down, then up, then down. All damn day.
Many parts later I did figure it out, but only after ignoring most of my friends/mechanics as to what 'couldn't possibly be' the issue.
Well, if you eliminate what's possible, the only logical next step... what's not possible.
anyway, during troubleshooting on this engine, I got some clear hoses of the right size and some joints and some stainless clamps. (Home Depot)
The idea is to add/replace the OEM hoses (temporarily) to see if you have air in your cooling system. This is primarily for open water cooling system, but I guess could be used closed loop too.
Start with the hose from the raw water pump to the thermostat - if it has no air in it (running boat in water, running off a hose will not give you answers since the water is under pressure) good. move on. You've confirmed your system is not sucking air into the cooling system. If it shows air in it, find the next logical place (lower unit to raw water pump) and see if that has air in it. Wherever you find air - your problem is before you see it.
In my case, it was no air until after the thermostat - so my engine was pumping air from the combustion chamber into the cooling system. Other than that didn't really have any ill effects, and since it ran, and was 20 years old - i just ran it as is rest of the season. End of the season I went to change the oil and found a milkshake for oil, so I replaced both base engines fall 2019. (myself) Put 100 hours on them first summer!
The temp fluctuations followed me to the new base engine (but the milkshake oil did not)... about 1/2 way through the new season (and lots of troubleshooting) later I determined it was the thermostat housing that was the issue.
I don't take credit for the original idea. Dodge on another forum I think told me about it.
This engine would start and run 'fine', but the temp would go up, then down, then up, then down, then up, then down. All damn day.
Many parts later I did figure it out, but only after ignoring most of my friends/mechanics as to what 'couldn't possibly be' the issue.
Well, if you eliminate what's possible, the only logical next step... what's not possible.
anyway, during troubleshooting on this engine, I got some clear hoses of the right size and some joints and some stainless clamps. (Home Depot)
The idea is to add/replace the OEM hoses (temporarily) to see if you have air in your cooling system. This is primarily for open water cooling system, but I guess could be used closed loop too.
Start with the hose from the raw water pump to the thermostat - if it has no air in it (running boat in water, running off a hose will not give you answers since the water is under pressure) good. move on. You've confirmed your system is not sucking air into the cooling system. If it shows air in it, find the next logical place (lower unit to raw water pump) and see if that has air in it. Wherever you find air - your problem is before you see it.
In my case, it was no air until after the thermostat - so my engine was pumping air from the combustion chamber into the cooling system. Other than that didn't really have any ill effects, and since it ran, and was 20 years old - i just ran it as is rest of the season. End of the season I went to change the oil and found a milkshake for oil, so I replaced both base engines fall 2019. (myself) Put 100 hours on them first summer!
The temp fluctuations followed me to the new base engine (but the milkshake oil did not)... about 1/2 way through the new season (and lots of troubleshooting) later I determined it was the thermostat housing that was the issue.
