Mordy Dunst/Gasket Works USA, LLC wrote:
> Question:
>
> I have a motor home with an 8.3 l cummins diesel pusher. the coolant
> radiator is on the rear and side of the coach. This radiator is probably 48
> inches wide and possibly 30" tall. It is cooled by two fans powered by
> hydraulic motors. The system seems very complex. It has dual hydraulic oil
> filters lots of high presure hoses and a special gilmer cog belt drive for a
> large hydraulic pump driven off the crankshaft. this belt is very expensive
> (about $300.00) and is not an automotive belt, but instead is an
> industrial belt not at all easy to get. It took some doing to find a spare.
>
>
>
> The point is ... Why did the engineers do this? why not two or four
> electric fans thermostatically controlled?
>
> I'm tempted to take this maze of hydraulic pumps, filter, motors, hoses and
> accumulator tanks and toss them.... and replace by two or four electric
> fans....
>
> comments that would shed some light on this would be appreciated.
>
> Please answer directly if you like...
Mordy, I can't for the life of me figure out why hydraulic fan drives have
persisted. Where I've been working for the
past thirteen years, we produced transit buses with transverse-mounted engines,
so the radiator was always mounted on
the left rear of the bus, because that enabled direct fan drive from the
engine. When the powers that be decided they
needed a t-drive arrangement (to compete with other manufacturers), they still
retained the left-side radiator and chose
a _very_ expensive hydraulic drive arrangement to run the fan, even though
previous experiments with mechanical and
hydraulic drives had failed miserably. Their most recent attempt in this regard
added, by my calculations, $4700 to the
cost of the bus. Made no sense at all.
At least one other manufacturer has had a thermostatically-controlled electric
fan motor for all cooling requirements at
about 1/4 the cost of hydraulic arrangements. It works well and is more
reliable than hydraulics, which leak, even with
careful attention. But, for many transit agencies, adding some hydraulic fluid
at fuel stops is cheaper and easier than
maintaining another electrical system.
That said, for motor home use, electrics would be far preferable, as long as
there were adequate controls to prevent
overheating. I don't know what C-series Cummins you have installed, but the
later ones (those with integral injector and
fuel distributor) do have an electronic control in the computer for engine fan
tied to the engine heat sensor output, so
thermostatic control would be easy with that. Earlier mechanical engines would
require an additional sensor in the
system for such control.
There are distinct advantages in having electric fans--that's why most auto
manufacturers have reverted to
them--single-speed motors coupled to fan blades designed for optimum efficiency
at that speed have pronounced effects on
mileage compared to variable-speed engine-driven fans, and on cost, compared to
the complexities of speed control for
hydraulic systems.
Maintenance seems to be the issue--if one keeps pumping fluid into the
hydraulic system, it continues to work, well
enough to get by. When some part of an electrical cooling system quits, it
quits completely and overheating results.
Keep on top of the maintenance, and an electrical system is simpler and cheaper
to operate.
Cheers.
--
Michael D. Porter
Roswell, NM
[mailto:mporter@zianet.com]
Never let anyone drive you crazy when you know it's within walking distance.
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