Mercruiser 470 3.7L Coolant Issue

[bikemtn]

I have fresh rebuild still under warranty on a 470 Mercruiser. I have had no issues with the motor, but the last few times it seems that the coolant level is low. Last time I went out the level was super low. So I added to the resevoir and the aux tank.... It is not leaking at the cam seal or anywhere inside the bilge. I am thinking that it is being exhausted somehow? Could the heat exchanger be bad? Does not overheat, etc...Oil is clean, bildge is clean......

1988 model...4" exchanger....alternator conversion

 

[Maclin]

Re: Mercruiser 470 3.7L Coolant Issue

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.

 

[bhammer]

Re: Mercruiser 470 3.7L Coolant Issue

I would pressure test the whole system for sure. You can pick up the pressure tester at the automotive store. Just listen for where it is escaping from. You can remove the fore and aft end caps from the heat exchanger and listen there.


I had a radiator shop repair a heat exchanger for under $50.

 

[winter$4]

Re: Mercruiser 470 3.7L Coolant Issue

I had the same problem and it ended up being the gasket between the manafold and the resevior had cracked allowing coolant to leave with the exhaust. the gasket was less than $10.

 

[bikemtn]

Re: Mercruiser 470 3.7L Coolant Issue

I dropped the boat off at the mechanic as it is still under warranty...They said they pressure tested the system cold and hot and could not find any leak????? Said they have a call into the Mercruiser Tech. I told them the coolant was going somewhere!!!! I am not convinced that they could not find a leak

 

[bikemtn]

Re: Mercruiser 470 3.7L Coolant Issue

Just wanted to follow up and let the guys that helped know what I did to fix my leak.
The riser looked to be original so I went ahead and ordered a new one and a new gasket. Went in super easy. I decided that I better go over the whole engine and see if I could find any obvious coolant leaks. I could see staining along the side of the block behind the starter. Looked like the head gasket was leaking!!!! Pulled out my manual and it stated that the head needs to be retorqued after the initial run (fresh rebuild). I retorqed the head per the manaul and the leak is gone!!! Thanks for all the help guys!!! It was very appreciated.