common coolant leak points

[redbeard1]

Hello all,



Our engine was recently run for about an hour without raw water. I just about fixed the damaged exhaust system but today discovered anti-freeze under the water heater. Our system has AF cooled via heat exchanger which is cooled by raw water.



Our AF reservoir is aft of the water heater and the AF hoses run from the water heater to the reservoir than back to the engine. see attached drawing.



There is no spilled coolant around the reservoir. see picture



My questions - Isn't the reservoir supposed to have a release valve in the cap? Do water heaters commonly have relief valves? Is a leak from a hose the most likely scenario?

[skipperpete]

I have no helpful insights into where the coolant leaked from but I'm impressed by the diagram.... it resembles our "hash house harriers" course, complete wit refreshment stops.

[DougR]

An hour without raw water?? Wasn't your overheat alarm screaming at you?

My guess is that the pressure cap on the expansion tank opened and the antifreeze overflowed and then ran under the hot water tank. The opening pressure of the cap is moulded into the top of the cap. Might not be a bad idea to have the opening pressure of the cap checked. Of course it could have leaked from a loose hose clamp instead....

Hot water tanks do have relief valves, but they are on the heated water side, not on the antifreeze coil side.

What I'm surprised at is that the engine isn't cooked! Maybe the hot water tank absorbed some of the heat...?

DougR

[Nicholson58]

The reservoir cap, same as the radiator cap on your car, is spring loaded and will release on over pressure. You will get additional cooling as your coolant boils. This will afford some cooling for a short time. There is usually a small drain hose from the fill cap to the bilge or more likely, the auxiliary expansion tank. Perhaps you needed new hoses anyway. if you ran the raw water pump dry it may need a new impeller.

Other leaks, all bad:

the coolant can leak into the water heater through the internal heating pipes.

Coolant pump seal.

Leaking heat exchanger into the wet exhaust.

[jamhass]

My last "hard to find" coolant leak on my Volvo 2003t proved to be the coolant pump seal. Only dripped very slowly when running. Passed pressure test fine when not running. Have had other slow seeps from the various and multitude little rubber seal rings ubiquitous to that engine.

[redbeard1]

Originally Posted by DougR

An hour without raw water?? Wasn't your overheat alarm screaming at you?
DougR

Thanks for reply. I was not the skipper. It is a sailing club boat and times like this make me wonder about our mission statement.

Originally Posted by DougR

My guess is that the pressure cap on the expansion tank opened and the antifreeze overflowed and then ran under the hot water tank.
DougR

That was my guess as well. I'm confused why the cap and tank look so clean (picture). When my car coolant hose cracked, the dried coolant was easy to see and track back to its source. Instead, this reservoir is clean.

Originally Posted by DougR

What I'm surprised at is that the engine isn't cooked! Maybe the hot water tank absorbed some of the heat...?

DougR

Skippers usually use the engine for 15 minutes leaving and 15 minutes returning. Just enough time to get out of the harbor (harbor has no wake rule so revs are kept near minimum) and raise sails and then douse sails and return to the dock. Two skippers x 2 round trips equals my guess of 60 minutes.



I guess it took a while for the cold engine to heat up without the raw water, probably because of your guess (water heater). Both skippers claim the alarm only sounded for a few minutes before they shut engine off (either because they were ready to raise sails or because they were docked).



I think the club got very lucky. To my untrained ear, the engine sounds as before and we saved a 5-10 thousand bill. The impeller was completely shredded, some hoses and the muffler needed to be replaced. And whatever/if anything will need to be fixed for the coolant leak.

[redbeard1]

Nicholson58 and Jamhass,


Thanks for the ideas. I'll look at those areas when I'm next on boat.

[redbeard1]

Hello,


Thanks for all the replies. I just wanted to write a quick note to report final outcome on the thread.



On closer inspection, there appears to be some coolant residue under the reservoir tank and no traces anywhere else in the coolant circuit. I can't easily inspect the coolant connections behind the water heater, but for now I'm going to assume the leak came from the reservoir. Maybe in the spring, I'll try to inspect the water heater.


We just motored for six hours to get out boat to winter storage without incident. Final list of damage from overheating was : lift muffler, impeller, an exhaust hose, thermostat, oil change, coolant change (we had to add 105 ounces to a 185 ounce system - we apparently lost more than half of our coolant).