1988 Mercruiser 3.7 Liter LX 4cyl.

[CadillacMan]

I have had this boat out twice,and it has failed me both times. The port engine keeps overheating after about 2 hours of mild operation. It has a closed cooling sytem. I found after trying to pressure test this sytem that all my coolant was being expelled out the out drive. I took off the what ill call a radiator cap,put a pressure testing device on it,and i heard a gurgling noise from the sterndrive. It would not hold pressure. The boat was in the water at this time. All the coolant was gone from the reservoir. I did this same procedure on my starboard engine and it held pressure. I am stumped at this point as how the coolant can escape a sytem that is suppose to be a closed system. My starboard engine was overheating as well. I replaced the impeller and it seemed to fix that engine's overheat problem.

Any help would be greatly appreciated.

 

[bomar76]

Re: 1988 Mercruiser 3.7 Liter LX 4cyl.

A bad heat exchanger would be the most obvious culprit.

 

[Maclin]

Re: 1988 Mercruiser 3.7 Liter LX 4cyl.

CadMan,

There are two chambers in the heat exchanger. The inner chamber holds the engine antifreeze and is like the radiator in a car. This is the closed part of the system The outer chamber is what the raw water pump pushes the cooling water thru to take the heat away from the inner chamber "radiator", this cooling water exits thru the exhaust. If the inner chamber has ruptured then the antifreeze will exit under pressure into the outer chamber and flow out thru the exhaust. On a car the antifreeze would just run out on the ground and you would know it was leaking.

Circulating water around a radiator is more efficient way of removing heat than is an air cooled radiator so the units can be much smaller.

 

[CadillacMan]

Re: 1988 Mercruiser 3.7 Liter LX 4cyl.

Thank you.

I will take the exchanger off and remove the gaskets and see if I can see a rupture inside these chambers. I put new gaskets on the ends last year.

I appreciate your time and explanation. I now have a better understanding of how these systems work.

CadillacMan

 

[Don S]

Re: 1988 Mercruiser 3.7 Liter LX 4cyl.

99% Chance you won't be able to see the problem. Pressure check it and see if it will hold pressure.