A funny thing happened on the way thru an oil change

"Jan Kalin" > wrote in message
...
> In article >, Ross Garrett wrote:
>>
>>"Malt_Hound" > wrote in message
...
>>
>>> Which brings me to another thought... why do we need fans that run
>>> directly off the engine, increasing and decreasing with engine speed,
>>> when
>>> in all reality, the biggest need for additional air flow thru the
>>> radiator
>>> will be at the lowest engine speed, and the least need for the fan will
>>> be
>>> at higher rpm when we are making good speed?
>>>
>>> Seems like an intelligently controlled electric fan would be a better
>>> design, no?
>>
>>I am pretty certain the new era of BMW's have electric radiator fans. I
>>thought I read somewhere that is one of the means they used to lower
>>engine
>>loading to increase power yet maintain fuel efficiency (apparently better
>>battery capabilities mean less load without the fan belt, but also no
>>increased load for the alternator). The fan and fan speed are driven by
>>signals from the engine controller. I also think they might have electric
>>water pumps for the same reason.
>>
>>And I know both my E39's had at least some semblance of an electric fan
>>because it would run long after the engine shut down on hot days when the
>>AC
>>had been used.
>
> That's the auxillary electrical fan for cooling AC condenser. The main fan
> is mechanical with a viscous clutch. Check out
> http://www.realoem.com/bmw/partgrp.d...44&hg=11&fg=35
> for the main fan (located between the radiator and engine) and
> http://www.realoem.com/bmw/partgrp.d...44&hg=64&fg=55
> for the AC fan (located in front of the radiator).

Thanks. I was wrong on the new cars' water pump too. The site clearly shows
the water pump and alternator run from the same belt.

In article >,
Ross Garrett > wrote:
> Thanks. I was wrong on the new cars' water pump too. The site clearly
> shows the water pump and alternator run from the same belt.

Thing is if you're going to drive an alternator from a belt and then use
that electricity to drive a waterpump and fan, you might as well drive the
waterpump and fan directly. When we get high voltage alternators that are
part of the flywheel so no friction from the drive, things might be
different. I dunno how much power a waterpump devours, and whether the
ability to vary its output independant of engine speed would be useful or
not, though. But I'd say viscous coupled fans are pretty efficient - and
rather longer lived than the average electric fan - if the aux one on the
E39 is anything to go by. ;-)

--
*Certain frogs can be frozen solid, then thawed, and survive *

Dave Plowman London SW
To e-mail, change noise into sound.

"R. Mark Clayton" > wrote in message
...
> ----- Original Message -----
> From: "Malt_Hound" >
> Newsgroups: alt.autos.bmw
> Sent: Wednesday, July 06, 2005 2:16 AM
> Subject: A funny thing happened on the way thru an oil change
>
>
> snip
>
> > Which brings me to another thought... why do we need fans that run
> > directly off the engine, increasing and decreasing with engine speed,
when
> > in all reality, the biggest need for additional air flow thru the
radiator
> > will be at the lowest engine speed, and the least need for the fan will
be
> > at higher rpm when we are making good speed?
> >
> > Seems like an intelligently controlled electric fan would be a better
> > design, no?
> >
> > -Fred W
>
> BMW fans are viscously coupled - engine cold - fan slips ; engine hot fan
> spins.
>
> Electric fan should cut in if engine get too hot (e.g. in traffic), but
> represent a potentially disastrous failure mode if relied on completely.
>
> I should try and find out why the fan blades broke - any sign of the
remains
> of the neighbour's cat that hid under the bonnet.
>

No signs of the cat. Well, there wasn't any fur on the plastic parts that I
found. I did have some service recently, and I found that the fan shroud
wasn't fully clipped into place. I don't know that it came unclipped as a
result of the fan coming apart, or caused the fan to come apart. The shroud
is in good shape considering the other distruction in the area.

R. Mark Clayton wrote:
> ----- Original Message -----
> From: "Malt_Hound" >
> Newsgroups: alt.autos.bmw
> Sent: Wednesday, July 06, 2005 2:16 AM
> Subject: A funny thing happened on the way thru an oil change
>
>
> snip
>
>
>>Which brings me to another thought... why do we need fans that run
>>directly off the engine, increasing and decreasing with engine speed, when
>>in all reality, the biggest need for additional air flow thru the radiator
>>will be at the lowest engine speed, and the least need for the fan will be
>>at higher rpm when we are making good speed?
>>
>>Seems like an intelligently controlled electric fan would be a better
>>design, no?
>>
>>-Fred W
>
>
> BMW fans are viscously coupled - engine cold - fan slips ; engine hot fan
> spins.
>
> Electric fan should cut in if engine get too hot (e.g. in traffic), but
> represent a potentially disastrous failure mode if relied on completely.
>
> I should try and find out why the fan blades broke - any sign of the remains
> of the neighbour's cat that hid under the bonnet.

Yeah, but my SAABs with 4 cylinder transverse engines all had electric
fans, and they were pretty darn reliable. They worked simply on the
thermostatic switch that measured the coolant temp in the radiator. So
long as the coolant in there was OK then the cooling system should be
able to regulate properly via the regular coolant thermostat.

The nice thing about that design is that when you are traveling at a
decent speed (45mph+) the forced airflow through the radiator is more
than the little fan can create so it does not need to run.

OTOH, there is a 2 speed control on the SAAB fan so that with the AC on,
or if the temp gets above a secondary threshold the fan goes into warp
drive.

This really seems to be a more intelligent design to me...

-Fred W

Dave Plowman (News) wrote:
> In article >,
> Ross Garrett > wrote:
>
>>Thanks. I was wrong on the new cars' water pump too. The site clearly
>>shows the water pump and alternator run from the same belt.
>
>
> Thing is if you're going to drive an alternator from a belt and then use
> that electricity to drive a waterpump and fan, you might as well drive the
> waterpump and fan directly. When we get high voltage alternators that are
> part of the flywheel so no friction from the drive, things might be
> different. I dunno how much power a waterpump devours, and whether the
> ability to vary its output independant of engine speed would be useful or
> not, though. But I'd say viscous coupled fans are pretty efficient - and
> rather longer lived than the average electric fan - if the aux one on the
> E39 is anything to go by. ;-)
>


Well, sort of... My thought was with electric auxiliaries, you can turn
them on and off with intelligent controls rather than just having them
run all the time that the engine is running.

For instance, running a water pump full time, or the fan full time, even
though the engine may not need them.

I also recall reading somewhere that a pusher fan is more efficient than
a puller type such as one driven off the engine.

-Fred W

"Dave Plowman (News)" > wrote in message
...
> In article >,
> Ross Garrett > wrote:
>> Thanks. I was wrong on the new cars' water pump too. The site clearly
>> shows the water pump and alternator run from the same belt.
>
> Thing is if you're going to drive an alternator from a belt and then use
> that electricity to drive a waterpump and fan, you might as well drive the
> waterpump and fan directly.

Well maybe the water pump. The heat generated inside the engine is
generally proportional to rev's and a bit dependent on load, so the flow of
cooling water should vary with engine speed, which it will do if the pump is
directly driven.

The operation of the fan depends on the amount of heat generated, but also
on how difficult it is to get rid of. Factors such as ambient temprature,
current block temperature, speed of the car, wind, is it raining, use of the
in car heater etc. all affect how fast the fan will need to go to dispose of
the suprlus heat.

> When we get high voltage alternators that are
> part of the flywheel so no friction from the drive, things might be
> different. I dunno how much power a waterpump devours, and whether the
> ability to vary its output independant of engine speed would be useful or
> not, though. But I'd say viscous coupled fans are pretty efficient - and
> rather longer lived than the average electric fan - if the aux one on the
> E39 is anything to go by. ;-)
>
> --
> *Certain frogs can be frozen solid, then thawed, and survive *
>
> Dave Plowman London SW
> To e-mail, change noise into sound.

"Malt_Hound" > wrote in message
...
> Dave Plowman (News) wrote:
>> In article >,
>> Ross Garrett > wrote:
>>
>>>Thanks. I was wrong on the new cars' water pump too. The site clearly
>>>shows the water pump and alternator run from the same belt.
>>
>>
>> Thing is if you're going to drive an alternator from a belt and then use
>> that electricity to drive a waterpump and fan, you might as well drive
>> the
>> waterpump and fan directly. When we get high voltage alternators that are
>> part of the flywheel so no friction from the drive, things might be
>> different. I dunno how much power a waterpump devours, and whether the
>> ability to vary its output independant of engine speed would be useful or
>> not, though. But I'd say viscous coupled fans are pretty efficient - and
>> rather longer lived than the average electric fan - if the aux one on the
>> E39 is anything to go by. ;-)
>>
>
>
> Well, sort of... My thought was with electric auxiliaries, you can turn
> them on and off with intelligent controls rather than just having them run
> all the time that the engine is running.
>
> For instance, running a water pump full time, or the fan full time, even
> though the engine may not need them.
>
> I also recall reading somewhere that a pusher fan is more efficient than a
> puller type such as one driven off the engine.
>
> -Fred W

One idea I like with the electric fan and water pump is the car can then
continue to run them after the engine is off until the engine temp gets
below a set temp.

In article >,
Malt_Hound > wrote:
> Yeah, but my SAABs with 4 cylinder transverse engines all had electric
> fans, and they were pretty darn reliable.

With a transverse engine and a front mounted rad it would be difficult to
have an engine driven fan...

--
*If at first you don't succeed, redefine success.

Dave Plowman London SW
To e-mail, change noise into sound.

In article >,
R. Mark Clayton > wrote:
> > Thing is if you're going to drive an alternator from a belt and then
> > use that electricity to drive a waterpump and fan, you might as well
> > drive the waterpump and fan directly.

> Well maybe the water pump. The heat generated inside the engine is
> generally proportional to rev's and a bit dependent on load, so the flow
> of cooling water should vary with engine speed, which it will do if the
> pump is directly driven.

> The operation of the fan depends on the amount of heat generated, but
> also on how difficult it is to get rid of. Factors such as ambient
> temprature, current block temperature, speed of the car, wind, is it
> raining, use of the in car heater etc. all affect how fast the fan will
> need to go to dispose of the suprlus heat.

Hence the temperature sensitive viscous coupling? And I'd suggest a BMW
one is more powerful when locked up than any electric one.

--
*Warning: Dates in Calendar are closer than they appear.

Dave Plowman London SW
To e-mail, change noise into sound.

"R. Mark Clayton" > wrote in message
...
>
> "Dave Plowman (News)" > wrote in message
> ...
>> In article >,
>> Ross Garrett > wrote:
>>> Thanks. I was wrong on the new cars' water pump too. The site clearly
>>> shows the water pump and alternator run from the same belt.
>>
>> Thing is if you're going to drive an alternator from a belt and then use
>> that electricity to drive a waterpump and fan, you might as well drive
>> the
>> waterpump and fan directly.
>
> Well maybe the water pump. The heat generated inside the engine is
> generally proportional to rev's and a bit dependent on load, so the flow
> of cooling water should vary with engine speed, which it will do if the
> pump is directly driven.

That is true and has worked for years, but given the need to enhance power
while lowering fuel consumption, an electric driven water pump and radiator
fan makes a lot of sense. I agree with Fred on this. I found the article I
was lloking for, and BMW is using an electric water pump (engine cooling,
not just heater core flow) in the E90...and their results indicate the
savings from the pump compared to the increased load on the alternator, is
well worth the change.