Loosing Coolant but can't find out where

[millterr222]

Hey all, new to iboats!

I have a 1989 5.7L Mercruiser that I have been slowly restoring on my 1989 Sportcraft Fishmaster 23'. Last week, after taking my boat out I noticed the temps rising within 20 minutes of running and stopped the engine. Noticed coolant was low, so I refilled the tank, about 3 quarts worth, (luckily I always pack extra of everything). Ran it for another 15 minutes and engine temps started creeping up again. Rechecked coolant levels and noticed it was all gone. Refilled her a final time (emptied the coolant bottle) and brought her back in and started looking. Oil seems fine. Pulled the dipstick while on the water, on the ramp and back at home, no milkiness of any kind. Did I rule out cross contamination/ blown head gasket?

I recently pulled the heat exchange and there was almost no debris or scaling of any kind. Looks like there is no saltwater/coolant mixing from inspecting tubes. I am now going through the rubber connecting tubing to look for any kind of damage but am so confused on what this could possibly be. Thanks for your help.

 

[Scott Danforth]

have your heat exchanger pressure tested.......

 

[Bondo]

Ayuh,...... Welcome Aboard,....... Are the exhaust manifolds on the freshwater side, or the raw water side,..??..??

 

[tpenfield]

The coolant is probably going out with the raw water . . .

So, as mentioned, you probably have a leak in the heat exchanger . . . or . . . if you have coolant running through the exhaust manifolds, then there could be a leak in the gasket sealing them from the riser/elbow.

Closed cooling systems are easy to pressure test, so have at it.