Overheating Raw-Water Cooled Volvo

[coma]

Hi,
Sorry I can't help you with your problem, but as another MD5 user I'd like to ask you several questions.
What size prop are you running? Mine is 14x7 pushing a 5200# 26' Chrysler 26 and doesn't seem to achieve max rpm., although I can hit 5.8 knots.
Mine seems to smoke at all rpm settings,leaving soot on the transom. I've read a little about injection angle but can't find info about checking it that I can understand.
The boat is new (to me!) and I haven't had much time yet to sort things out. I should try running it on the water with the alternator disconnected as it's a 66 amp Delco and was a problem when I first tried to start it!

thanks, Lamont

[danielb]

Hi Lamont, I also have a 14x7 folding prop on a Volvo Saildrive.
My boat is 25.5 foot 1800+ kg. I get max 5.8-6 knots on GPS when the bottom is clean, and there's no opposing wind/tide. Not sure about RPM (need to fix my RPM gauge), but I have a tiny bit of throttle left at this speed. If I open the throttle fully, it only sounds like an extra 100RPM or so but makes very black exhaust water!
My engine smokes (light grey) a little even when warm and under light load. I don't seem to use hardly any oil so put it down to slight overfuelling. Apparently Volvos are renowned for being a bit smokey even when in good condition.
That alternator may rob you of a bit of power when the batteries are low. The standard alternator is only 35amp.
Let me know if you have any other questions - I've done a fair bit of work on this engine!

Regards,
Daniel

[danielb]

Thanks Everyone for the suggestions, I have resolved the problem.

Turns out that my custom thermostat housing was to blame.

Water entered the housing, then went straight out the exhaust. Even when the thermostat opened, this was the easiest path, so there was very little circulation throught the head and block.

A modification to the housing restricted flow between the inlet and the outlet to exhaust elbow (made it 50% smaller hole than 'prefered path'). This 'encourages' correct flow path, but still allows it to go out the exhaust while thermostat is closed. The new housing opened everything up too much, and did not direct the flow.

Now sits at 62-67 degrees under load - much happier about that than 80+.

[larrys]

I also operate a 30 year old Volvo MD5A engine with a 1.91:1 MSB reverse gear. Engine and gearbox are raw water cooled. In forward at full throttle, the engine runs fine, but the gearbox seems hot. Can anyone tell me the gearbox normal operating temperature?