www.iFourWinns.com

l have a 2007 358 Vista with twin 5.7 GXLI-H Volvo Penta inboards with closed cooling. The port engine has been gaining coolant and I suspect a heat exchanger leak. My question is two-fold. First isn't the closed cooling side pressurized? I would expect if that's the case, I would be losing coolant not gaining. We don't see signs of antifreeze coming out the exhaust. All fluid levels are normal and the engine is operating at normal temperature (175 Deg. F). I have not yet pulled the end-caps off the heat exchanger to see if there are any signs of leakage at that level, but I would suspect since I'm gaining level that I won't see any signs there either. Any thoughts as to what a good diagnostic check would be?

Yes, the "antifreeze" side of the heat exchanger is pressurised, as is the antifreeze mix that recirculates in the engine. There is also an expansion tank.

The pressure cap on mine ( VP aftermarket kit) is actually on the heat exchanger and the expansion tank is not pressurized. On the VP kit I had on my previous enzgine, the pressure cap was actually on the expansion tank. Is this gaining of coolant reversible, or does it continue to rise and rise??

If reversible bear in mind the coolant will expand as it gets hot and the level in both the expansion tanks will rise. If it starts to boil though, the expansion is much greater. The pressure cap basically suppresses boiling.. Maybe one pressure cap is leaking so little pressure is being generated; you could try swapping them over.

If it is not a reversible rise, I can't think from where / how water could get into a pressurised system, again, unless it wasn't pressurising properly.

Graham

Thanks for the post.

Unfortunately, the cooling gain is pretty continuous. I would think that after shutdown, since the raw water side is no longer flowing/generating pressure, and the coolant side is pressurized from expansion, it would want to leak back/drain to the raw water side. I actually noticed a slight increase in fluid late last season and it appears to be getting worse this season. I've actually removed fluid from the expansion tank a few times this season (last time it was a 12 oz bottle) so as to not overflow into the bilge. I've been told the problem could be either the heat exchanger or the exhaust manifold by a few folks thus far. I'm going to try and pressure test the system. I'm planning a short trip this weekend and will try swapping the caps, but the fact that raw water is coming in indicates a leak that shouldn't be there.

A pressure test should reveal something. As a matter of interest, do you boat in salt water? If so, have the heat exchanger anodes been changed every year ? ( I find mine need changing every year). Slight corrosion on one of the soldered joints could result in a pinhole. The raw water pump does generate some pressure, possible enough to force water into the coolant when the engine is cold, before the coolant side becomes pressurised.

Graham

It's a freshwater boat. I have not checked the anodes this season (I should know better). We'll see what we find...