MD7A Raw Water Cooling Temp

[Joe Amorese]

First off, thank you for the wealth of information this board has provided. I purchased a 1980 CD28 # 258 this spring. Everything on the boat was in great shape except an annoying drip coming from the thermostat housing. I finally got around to replacing the supply water o-ring. The temperature gage prior to replacing the o-ring never went past the white and the previous owner said it always ran at that temperature. Now the temperature gage goes to the “T” with the engine at 1000 rpm. At full throttle 2200 rpm the needle modulates around the “M” in TEMP just below the red scale. I then replaced the thermostat same thing. Replaced the impeller same thing. Checked the thermostat in a hot water it opens at 140. With the thermostat out the needle does not move off the low end. This boat has always been in fresh water the thermostat housing has no corrosion or blockage so I am assuming the block is in the same shape. I have no idea why the temperature gage registers now but I am concerned that I might overheat. My next step is to calibrate the sending unit. Any suggestions? Where should the needle be at normal operations? The water temperature in Lake Ontario is in the mid 70’s

Thanks,
Joe



jamorese@rochester.rr.com

[John MacArthur]

snip
Now the temperature gage goes to the “T” with the engine at 1000 rpm. At full throttle 2200 rpm the needle modulates around the “M” in TEMP just below the red scale.
snip

Thanks,
Joe

Joe -- My MD7A will get pretty warm at full throttle, too. I usually run it at about 1800 rpm, and it runs fine there. Keep full throttle for when you need it for a just a few minutes.

Johnny MacArthur
CD-30 "Stork"
Taos, NM &
San Carlos, Mex.



jmacNOSPAM@laplaza.org

[J Bierwert]

First off, thank you for the wealth of information this board has provided. I purchased a 1980 CD28 # 258 this spring. Everything on the boat was in great shape except an annoying drip coming from the thermostat housing. I finally got around to replacing the supply water o-ring. The temperature gage prior to replacing the o-ring never went past the white and the previous owner said it always ran at that temperature. Now the temperature gage goes to the “T” with the engine at 1000 rpm. At full throttle 2200 rpm the needle modulates around the “M” in TEMP just below the red scale. I then replaced the thermostat same thing. Replaced the impeller same thing. Checked the thermostat in a hot water it opens at 140. With the thermostat out the needle does not move off the low end. This boat has always been in fresh water the thermostat housing has no corrosion or blockage so I am assuming the block is in the same shape. I have no idea why the temperature gage registers now but I am concerned that I might overheat. My next step is to calibrate the sending unit. Any suggestions? Where should the needle be at normal operations? The water temperature in Lake Ontario is in the mid 70’s

Thanks,
Joe

Joe, check inside the 90's of the housing. I found an impeller lobe from the previous owner. Must have been there two years.



jbierwert@nisource.com

[John R.]

Double check your hoses at full throttle to make sure none of them are collapsing.

First off, thank you for the wealth of information this board has provided. I purchased a 1980 CD28 # 258 this spring. Everything on the boat was in great shape except an annoying drip coming from the thermostat housing. I finally got around to replacing the supply water o-ring. The temperature gage prior to replacing the o-ring never went past the white and the previous owner said it always ran at that temperature. Now the temperature gage goes to the “T” with the engine at 1000 rpm. At full throttle 2200 rpm the needle modulates around the “M” in TEMP just below the red scale. I then replaced the thermostat same thing. Replaced the impeller same thing. Checked the thermostat in a hot water it opens at 140. With the thermostat out the needle does not move off the low end. This boat has always been in fresh water the thermostat housing has no corrosion or blockage so I am assuming the block is in the same shape. I have no idea why the temperature gage registers now but I am concerned that I might overheat. My next step is to calibrate the sending unit. Any suggestions? Where should the needle be at normal operations? The water temperature in Lake Ontario is in the mid 70’s

Thanks,
Joe

[Larry DeMers]

Joe,

The MD7a/b should have a thermostat in it. I use the 190 Deg. thermostat (on Lake Superior, we have maybe 55 deg. water at it's warmest, usually closer to 40 deg. though), and the temp gauge will waver around the T in "TEMP", while at around 1500 rpm, and will waver around the M or P area when at 2000-2200 rpm for like 30 minutes or more. This is normal for this thermostat.

Yours is the cooler 140 deg. thermostat, which I would expect to hold the temp at the "T" on the gauge. I am considering getting a directly reading temp gauge and sender and replacing the existing unit, just so I can read the temp directly..the 'dumb' gauge, without calibration of numbers is near useless really...good for only a relative reading.

I would try maybe blowing compressed air thru the cooling passages, and see how open they are. You indeed may have something blocking them..it happened to me. I found 5 impellor blades in the passages when the engine was rebuilt. The only way to get them out is remove the thermostat and flush them out or blow them out. A thin wire may be of some help too. Ugh..nasty job.

Good Luck,

Larry DeMers
s/v DeLaMer
Cape Dory 30 Lake Superior

Thanks,
Joe

demers@sgi.com

[Larry DeMers]

Double check your hoses at full throttle to make sure none of them are collapsing.

-or sucking air!! (Good Point)

Larry

First off, thank you for the wealth of information this board has provided. I purchased a 1980 CD28 # 258 this spring. Everything on the boat was in great shape except an annoying drip coming from the thermostat housing. I finally got around to replacing the supply water o-ring. The temperature gage prior to replacing the o-ring never went past the white and the previous owner said it always ran at that temperature. Now the temperature gage goes to the ?T? with the engine at 1000 rpm. At full throttle 2200 rpm the needle modulates around the ?M? in TEMP just below the red scale. I then replaced the thermostat same thing. Replaced the impeller same thing. Checked the thermostat in a hot water it opens at 140. With the thermostat out the needle does not move off the low end. This boat has always been in fresh water the thermostat housing has no corrosion or blockage so I am assuming the block is in the same shape. I have no idea why the temperature gage registers now but I am concerned that I might overheat. My next step is to calibrate the sending unit. Any suggestions? Where should the needle be at normal operations? The water temperature in Lake Ontario is in the mid 70?s

Thanks,
Joe

demers@sgi.com