Closed cooling system help

[dwna1a]

I've got and had a issue with my closed system and I could use some help.

Ive got twin Mercs both have new risers and manifolds, new pumps and impellers. I did all this before my trip, they were due. Both engines run about the same temp with 115 thermostates (also new) All of you know I baby my 1750hr engines.

I have one reoccurring problem, once in awhile all the antifreeze goes missing from the heat exchanger and the engine runs hot. To hot for my liking but not overheating.

Question is, have I got a cracked tube or more, leaking the antifreeze into the exhaust or raw water? Do I pull the exchanger and have it tested or just replace the thing?

 

[magstang1]

Any evidence of coolant in the bilge? Mine burped 3-4 times before the level settled down. Check the small hose that goes from the filler neck to the overflow bottle. Mine had a little hole burned in the back and I would lose some every trip. Had a bad radiator cap too mine was 7 lbs.

I spent all summer chasing cooling problems. Add some details and I'll try to help.

 

[dwna1a]

There's none in the bilge at all and the overflow tube also looks to be good. Caps are fine as well. The first thought was a hole in the raiser gasket but now the gasket is new. I can go all month with no issue then suddenly it's all gone.

Only thing I can think of is to replace the exchanger, but that's just throw parts at a problem

 

[SCORPIO]

You can take the exchanger to a radiator shop and have it cleaned and pressure checked. I'd also smell the exhaust while its running and see if I could smell AF in the exhaust plume. I has a distinctive odor which would indicate a leak either in the manifold or a head gasket. My money is on the exchanger though, if its original to the boat, a tube(S) could have eaten through and causing your leak. Pull them and have them checked.

 

[dwna1a]

You can take the exchanger to a radiator shop and have it cleaned and pressure checked. I'd also smell the exhaust while its running and see if I could smell AF in the exhaust plume. I has a distinctive odor which would indicate a leak either in the manifold or a head gasket. My money is on the exchanger though, if its original to the boat, a tube(S) could have eaten through and causing your leak. Pull them and have them checked.

i called two different shops today..they will not test heat exchangers. Slip neighbor thinks he can test it, but no one can fix it. I hate throwing parts but maybe this time, I don't know

 

[mnm99]

i called two different shops today..they will not test heat exchangers. Slip neighbor thinks he can test it, but no one can fix it. I hate throwing parts but maybe this time, I don't know

It's easy to pressure test it. I just did it with my manifolds and elbow. Just have to go out and buy a couple fittings, clamps and a gauge.

 

[SCORPIO]

You can buy radiator pressure testers at auto parts stores, I have one. It fits on in place of the cap. All you have to do is block off the inlet and outlet tightly as show above and test it to the pressure your system normally runs, usually like 12-15 psi. As far as repairs if its bad, it may be a good idea to replace it if you can't get someone to repair it. I'd test first, shouldn't cost more than $40 for the supplies to do it. A new exchanger is close to $1000 EACH.

 

[Air O'Nautical]

Many auto parts shops will loan you the pressure tester free!
Just don't mention it's for a boat because, they'll think it won't fit.

Follow the instructions the kit has and you can trouble shoot several things without removing anything.

Just as a case for replacement parts many (me), suggest new heat exchangers at 10 years of service in a Mercuriser gas engines.
Repairing is a bandaid at best and it'll soon fail again at the worst possible time.

 

[dwna1a]

I ran her all afternoon up till about 11pm or so, she never lost a drop of antifreeze

 

[hottoddie]

You mention 115 degree thermostats. FWC cooled engines call for 160 degrees. The motors will run more efficient at 160. Also I could never understand the need for 14-15 PSI heat exchanger caps on FWC motors in a boat. I know the higher the PSI in the heat exchanger (radiator in a car) the higher the boiling point of the coolant. However boats run much cooler than car engines and don't require those higher boiling points. I replaced my caps 2 years ago with stainless steel 7 PSI caps and have never lost a drop of coolant.