I have a 525 EFI Merc that runs great but seems to be eating coolant at about a pint an hour. All temps and pressures are good but when I start it up I notice a very slight white sheen on the water from the water coming out of both pipes just at first.
The oil is normal, and all temps and pressures are normal. is it possible to have both head gaskets go at the same time? or is there somewhere else the coolant can leak in to the exhaust?
I have been adding coolant and running it but I don't want to hurt it.
The boat is a stag Gladiator and its the left engine

Do a leakdown. Might be a headgasket

have your heat exchanger pressure tested

ooh thats a thought, I assumed raw water cooled.

My bet is on the heat exchanger as well. If you are loosing antifreeze coolant, chances are you are mixing seawater in with your antifreeze (closed part of the system) too. If you are a saltwater boater, this is REALLY bad.

Where do you boat, and do you normally have to winterize? This could be the root of the issue. I'd check the other one while you are at it as well.

it looks like the heat exchanger for sure. I filled up the reservoir yesterday and it was down today from being static. I started it and the first fluid out of the pipes was the coolant.
I have been running it low for a while and it wasn't really changing. well the reason was is it was below where the leak is in the heat exchanger. when I filled up the reservoir to the cold fill line, the tank drained down and came out the pipes on start.
now where do I get a heat exchanger for a merc 525 EFI overnight.

its a fresh water lake I boat in. the boat has never been in salt. its in Idaho and I did have it winterized.

Good luck with the fix.
Call these guys in the morning:

http://www.mercruiserparts.com/
http://teaguecustommarine.com/

not sure what to order yet. what is a crossover? I see heat exchanger on the list but not sure of all I need.

I have a heat exchanger for 525 if needed.
Steve

I sent you a PM. is your exchanger new? price? where is it?