converting an older motor to fresh water cooling

[dtime]

I'm concidering purchacing and installing an monitor fresh water cooling kit for my 91 4.3 omc, and i have read that if the motor is an older one with long hours on it that it is not reconmended. i uss this boat in salt water and would loveto not need to run the salt thru the engine. the kit is for the engine only and the raw water will still exit thru the exaust risers. If any one has any experience with this kind of conversion the advice would be greatly appricated

 

[Haut Medoc]

Re: converting an older motor to fresh water cooling

100 hours or one year is the cutoff for the conversion, & you are well beyond that.....
Scale from the block will constantly clog the heat exchanger....
Consider doing it when you repower.......

 

[dtime]

Re: converting an older motor to fresh water cooling

thanks for the replay and under stand that the scale would be an issue is there any way to flush the block and descale it with the engine in it and operating? also i would not need to run anti freeze for i live in the southeast. I work with chemicals and occonally need to use a descaler in my trade to remove scale from in side of boilers. this motor runs like a caddy.really dont want to hurt it. and dont want ot destroy it by creating any troubles.

 

[bruceb58]

Re: converting an older motor to fresh water cooling

My understanding is that the salt leeches way into the block and then when anti freeze is used, it emulsifies so you are correct that you wouldn't want to use anti freeze for awhile.

As far as the scale, I have a feeling you will be cleaning your heat exchanger often. I went through the same thing you are going through right now. I had 125 hours on my engine and decided not to do it. Only half of my hours were salt. I spoke with an engineer at San Juan who was honest enough to give me his thoughts on not doing it.

 

[HydroDog]

Re: converting an older motor to fresh water cooling

100 hours or one year is the cutoff for the conversion, & you are well beyond that.....
Scale from the block will constantly clog the heat exchanger....
Consider doing it when you repower.......

Just a curious question? Does this apply to motors only run in fresh water also?
I purchased a 1991 boat this summer that has spent it's hole life in the rivers in the portland but would like to take it up to the Puget Sound more adventure boating. Or should I not worry about it and just flush out the motor with salt-a-way after every outing?

 

[joncrisler]

Re: converting an older motor to fresh water cooling

My understanding is that the salt leeches way into the block and then when anti freeze is used, it emulsifies so you are correct that you wouldn't want to use anti freeze for awhile.

As far as the scale, I have a feeling you will be cleaning your heat exchanger often. I went through the same thing you are going through right now. I had 125 hours on my engine and decided not to do it. Only half of my hours were salt. I spoke with an engineer at San Juan who was honest enough to give me his thoughts on not doing it.

I too spoke to the main guy at San Juan Engineering about a used motor conversion. It all depends on how much scale is in the engine, and you would expect more problems with a salt water engine than a fresh water engine. Its certainly doable, just depends on how rusty the inside of the block is, especially in the lower passages. Rigging up some sort of filter in the cooling system would be a nice thing to try, but cooling systems do not run enough pressure to offset any but the most coarse filter.

There was an article in DIY magazine where somebody converted a very old Atomic 4 (popular small snail-boat engine) to closed cooling with good results, but he rigged up a system to run muriatic acid through the engine to descale it first. I have not been able to locate that article since then, but it is probably on their CD collection.

 

[HT32BSX115]

Re: converting an older motor to fresh water cooling

Howdy,

I did my 1997 122hr since new, (fresh water) 7.4L engine 3 years ago using a San Juan system.

They told me that it would be ok and would work well. So far, It has......I used 50:50 DEXCOOL


So far no problems at all. I did remove a fair amount of loose rust in the block & manifolds.


Next year I'll probably drain the heat exchanger and block and have a look at what's in there.....



Cheers,


Rick