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Old 19-08-2009, 21:50   #1
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Engine Cooling Circuit - Choices

I have set up a heat exchanger (Bowman brand, from the UK; you just have to like it - it feels so nice and solid and heavily built) to convert my 36HP Bukh diesel from raw water to fresh water cooling. But I have to make a few choices - and welcome opinions on any or all of them.

A) Ideal Coolant Temperature:
My engine manufacturer's manual specifies the range of 160F - 200F for factory supplied cooling system (mine is third party custom).
At first I thought, go for the middle of this range. But then, a warmer engine is better for efficient and clean burning, so why not 200F? But is that a good idea in the long run (or for a long run) ... are there disadvantages to a higher engine temp setting?

B) Ideal Coolant Pressure Cap:
I also have to select a radiator cap for my coolant reservoir, and this cap will have a pressure relief rating. Manufacturer's manual is silent about this. Any recommendations for this rating?
(I am using an electrical circulation pump - Johnson magnetic drive)

C) Ideal Sequencing of Impeller Pump and Heat Exchanger:
I can place the heat exchanger before or after the raw water impeller pump. I thought, better to place it AFTER the pump. That way, the heat exchanger is not on the suction side and so I avoid air leaks, and it may be easier to spot water leaks (trickling out). But, there could be negatives ...

All opinions appreciated.
Martin
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Old 19-08-2009, 22:07   #2
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1. Are you using an electrical circulation pump for your coolant?

2. You want to pump cool water into the heat exchanger

3. I don't know what kind of reservoir you are using...I have seen reservoirs that are higher than the engine and they use gravity/expansion to achieve a proper level.

4. I would shoot for 160-180....that all depends on the thermostat you install.

I have serious reservations about an electrical circulating pump.
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Old 19-08-2009, 22:17   #3
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Quote:
Originally Posted by Chief Engineer View Post
1. Are you using an electrical circulation pump for your coolant?

2.
Yes Chief, Johnson electric pump CM30P7-1 (22.5L/min capacity, 15kPA or 2psi head).
According to the Johnson agent who sold it to me, it is intended for just such cooling circuit applications. Avoids another take-off from my space-challenged flywheel area.

Martin
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Old 19-08-2009, 22:26   #4
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That pump is rated for a max 100C or 212F range

I don't know what other respondents might say, but I am of the opinion that you may need to do a little more research into your choice of pump.

Remember...the guy that sold you the pump is not going to be sailing your boat.

Of course if you are going to use this to pump sea water thru your exchanger...then that should be ok.

If you are sailing in 200 degree water, YOU ARE IN SOMEBODYS" SOUP!!! Ha HA
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Old 19-08-2009, 22:34   #5
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Quote:
3. I don't know what kind of reservoir you are using...I have seen reservoirs that are higher than the engine and they use gravity/expansion to achieve a proper level.
Third party reservoir (separate from heat exchanger) situated at same height as rocker cover. Chief, are you saying I don't need a radiator cap?


Quote:
4. I would shoot for 160-180....that all depends on the thermostat you install.
I get to choose the thermostat, and its temp rating. Any opinion on why you feel 170 (midway between 160 and 180) would be better than say, 200F?


Re the choice of electrical circulation pump: Deep down, I don't like the idea, either. But when I work through the alternative of finding space and installing an external mechanical circulation pump with Power Take-off from another pulley on the crank, I succumb. I have a backup elec pump. The MTBF doesn't look too bad, but then, the figure is provided by the manufacturer ...
(Anyone want to chip in here with experience of using an electrical circulation pump on a diesel engine?)

Martin
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