I have a 2003
Volvo Penta engine with MS2
transmission and fresh water-cooling. The
engine worked fine last year, but this season it overheats at high rpms. The only change we made over the
winter was replacing the
exhaust hose with a slightly longer one, which shouldn’t matter. At 1500
RPM, it works fine with
raw water coming out of the
exhaust. At 2500
RPM in neutral it also works fine. At 2500 RPM with prop engaged, there’s a huge amount of steam coming out of the exhaust. This suggests to me that there is a blockage in the
raw water system, but how do I find it?
Checked so far:
1)Sea
water pump impeller. It had a large white shell in between two of the blades of the impeller. The impeller looked fine otherwise but I replaced it anyway. I had replaced the sea
water pump itself a year ago.
2)Exhaust
elbow. I’m told this is typically the cause of the problem. The old one looked ok, but I replaced it anyway.
3)Strainer. I dived under the
boat. As far as I could tell there was no blockage. It’s just a bunch of very thin slits there and I was able to stick a screwdriver through them, but not very deep. Not sure how that white shell could have passed through there, unless it actually grew in size within the raw
water system.
4)Heat Exchanger. Replaced it many years ago. Maybe I need to check it.
5)Hose loop attached to raw
water thruhull. The hose is old but it doesn’t collapse from the vacuum. Seems to
work.
Questions:
1)The first place the raw water enters, after the thru-hull and small hose loop, is the MS2
transmission (see photos). Does someone know if the
cooling rod can be removed from the MS2 and checked for blockage without removing the
propeller shaft that is above it? Does anyone have any pdf diagrams of the MS2 so I could see what’s inside and how to take it apart?
2)I don’t see a thermostat for the raw water side. I think I see what looks like a thermostat housing only for the fresh water
coolant. Am I seeing this correctly?
3)Where else could the blockage be? Should I just take all
parts of the system apart or is there another way to find the blockage?
4)I’m having trouble finding a
mechanic with any free time to look at this. Any suggestions? The
boat is in Norwalk, CT.
Aside:
The fresh-water engine
coolant must also be getting too hot since it’s not getting enough raw water
cooling in the
heat exchanger. It normally warms the hot water
heater, but now I’ve got hot water coming out of the relief valve of the hot water
heater into the
bilge. If I turn off the domestic water
pump so that the hot water heater does not fill from the water
tanks, the engine overheat
alarm goes off after about 20 minutes. This tells me that my domestic water system is now being used to partly cool the engine coolant; that eventually depletes all of the water in the fresh water
tanks.
Any
advice would be much appreciated.
Thanks,
Joe