Merc 260 closed cooling question

[Dogdave]

I have a 79 merc 260 with a San Juan cooling kit on it including the exhaust manifolds. My question is it pulls water from the alpha 1 impeller pump only. The original drive was pre alpha . The boat has been family owned since 81 and not changed. When I got it I put the alpha drive on and all new hoses and such. The engine puts out 311 hp on the dyno. My question is on a long run at 3400 rpm the temp gets to 185 to 190 on the gauge . Is this normal? Does the drive push enough water for the cooling system ? Should I not worry about it?

 

[Scott Danforth]

old motor and new kit? or refreshed motor and new kit? or old motor with kit installed years ago? salt water or fresh water?

if this is an old motor with a new kit - did you flush the block out? if it was run in salt water, it would be too late to install a closed cooling kit as the inner walls of your block would be all scaled over.

you should be running a 160-180 thermostat with a closed cooling system. that being stated, what does the block temp read with an IR thermometer (not your gauge - gauges are not that accurate) running 185 - 190 on the gauge would be normal with a full system under load for a long time considering the gauge accuracy of +/-15%.

are you saying the impeller has not been changed? if that is the case, change it.

if your gauge is dead nuts on - then I would keep an eye on it.
a few things to check:
raw water pump output - MC and Alpha pumps put out 19 gallons at 20 psi - at 1500 RPM, you should fill a 5 gallon bucket in about 16 seconds
debris in the heat exchanger. pull off the end covers and have a look.

 

[Dogdave]

Thank you, the cooling system was installed when the boat was new. I rebuilt everything 3 years ago block boiled, heads and heat exchanger last year. It is salt water only boat. I replaced the impeller last year for good measure. It runs a 165 stat. I have not checked the flow into a bucket though. Water pours out pretty good though

 

[Bondo]

Thank you, the cooling system was installed when the boat was new. I rebuilt everything 3 years ago block boiled, heads and heat exchanger last year. It is salt water only boat. I replaced the impeller last year for good measure. It runs a 165 stat. I have not checked the flow into a bucket though. Water pours out pretty good though

Ayuh,..... Pushin' over 300 hp, it could be the impeller pump is too small, or the heat exchanger is too small,....

Horsepower, equals fuel burn, which equals Heat,...

Yer bump in hp, mighta push marginal system over it's limits,....

 

[achris]

A 1979 MerCruiser-1 drive (no such drive as 'pre-alpha', and if I ever find the SOB that caused that term to become common use, I'll strangle the git) runs exactly the same water pump as an Alpha One... What rev are you making at wide open throttle? If it's not reaching the 4200 to 4600 range I suggest the engine is overloaded and that you account for extra heat in the cooling system....

 

[tpenfield]

I would add that the heat exchanger could becoming clogged, or perhaps you need a secondary pump running off the engine . . . The temp should not rise that much at the higher throttle ranges.

 

[Dogdave]

I think I'm propped right I can trim it out and hit 4850-4900 with a light load and 1 person in the boat. Cruises at 33-3400 @ 27 mph . 16 x16 prop. I had the heat exchanger boiled ( or maybe just painted) at a radiator shop. It is an earlier style 2 pass exchanger . I'll take IF thermometer readings this weekend and report back. Thank you

 

[Dogdave]

Well after the heavily loaded boat going out Saturday morning , running at 3800 rpm and we got hot half way to the destination. Limped in at idle at 190 degrees. We idled home , long day . Found that the alternator / water pump belt had lost a portion of the inner V . . New belts 60 hours ago. Pulleys look good . So hmmmm,m.