Potomac_Jerry

One of my 525 EFI's got hot last weekend. I felt a stagger at about 4000 rpm and saw the temp gauge at 210. I shut it down immediately and limped home.
The closed cooling system had spewed coolant all over my engine from the coolant reservoir cap.
The raw water pump was/is working fine (visible in strainer) and has a fresh impeller. At first I thought I had a thermostat failure but I added 4+ gallons of coolant/water over the course of 24 hours trying to test the system. I believe the closed system holds 14 quarts. If that is correct, how can I add 4 gallons of coolant and still have a low level unless it's leaking out ? I see no milky/nasty appearance on my oil dipstick and oil level is correct so I assume no coolant is getting into the engine. I see no visible leaks as the engine sits and runs on the lift. Does this indicate a bad heat exchanger ? Is it possible to get it tested or test it at home? I am thinking of doing a basic pressure test at 15 lbs like I would on a car cooling system. Is that a good place to start ??
THANKS for your help. Jerry

Mbam

Yes, start with a pressure test just like a radiator

Sydwayz

iTrader: (1)

Take it off, and put it on your workbench. Pull the endcaps off, and you will see where you need to cap it off and pressurize it. It's not a hard task. I went through this last year. There is a procedure in the Mercury Engine Manual for doing this while the H/E is still on the engine, however when I did this it was inconclusive (waste of my time). 7 hose clamps or so, and it pops right off. It's very easy to test with a couple of generic radiator hoses from Advance Auto and a couple of PVC pipe end caps; along with a rubber tip blow gun from an air compressor.

You can braise closed up to 3 of the tubes and still have it be cooling efficiently according to Mercury specs.
I ended up just replacing both of mine on my 496HOs. 1 of mine was bad. 1 of mine (off of 2003 496HO)...
http://www.mercruiserparts.com/bam/s...31823/6708/170 (part 15)
...is STILL GOOD. I can rent/sell it to you for the big weekend if it will work for your application. It's in my garage about 20 minutes due East of Kings Dominion.

And/or you can call Chris Dann at https://www.facebook.com/Rappa-Boat-...47046/?fref=ts
(804) 443-4434 in Tappahannock, VA He is a full Mercury/Mercruiser shop, and is quite tight with the Mercury Parts Warehouse in the Hampton Roads area. If they have it in stock, he can have it next day in Tappahannock, but you need to call him tomorrow if you need it by the weekend. Have your wallet and KY ready; they are not cheap.

**You will also want to replace the grommets between the Heat Exchanger and the crossover as these are a "wear item" and regularly fail/leak. I think I have a few of these as well, and any Merc Parts house can get them too.

Potomac_Jerry

Thanks for your input. I'm getting into it first thing tomorrow. I'll let you know what I find.
Jerry

paul buckner

Just help a friend with the same prob on a 496 Ho , coolent was disappearing no milky oil so we took off the Heat Ex and and tested it , just blew into it with latex gloves over the hose fittings and it was leaking .
Found a replacement from a Mr cool $ 680 as sydwayz said replace the rubber fittings .
Can pass number onto you if you need it .paul