A funny thing happened on the way thru an oil change

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I was changing the oil in my car, and while waiting for the dripping to stop, I looked around at all of the stuff there is to look at under a car, and wondered what all of the plastic parts were that were laying around near
the bottom of the radiator. It hit me that the fan was gone. The plastic parts were the remants of the fan blades. The fan was completely gone.
I had no idea from the guages or anything else that the fan wasn't with me anymore. Indeed, I have been wondering if the motor runs too cold in the morning because I have seen the guage take forever to reach the mid point of the scale, then over the course of a mile or so on the freeway, the needle will drop to the blue and slowly rise back to the mid point again. I was guessing that the tstat might be stuck open, but I had no idea that the fan wasn't there. I would expect the engine to get very hot, at least is slow moving traffic on a hot day, if the fan was not working, but there was no indication whatsoever.
The fan is very easy to replace, one reverse-threaded nut on the fan clutch and three small allen screws. That's it.
I just wanted to share ...
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Jeff Strickland wrote:

That is a funny one, Jeff. But I suppose one would never notice their lack of a fan unless, or until, they get stuck in traffic and need to stand stationary for a while.
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
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Years ago, I had a 1971 Ford truck. the fan was bolted straight to the water pump. It didn't matter much since the engine didn't go much past 4000 RPM anyways.. However, in the newer cars. they have a fluid clutch, so when its cooler, the fan almost completely slips. As it gets hotter, the clutch will engage more and more until its fully locked. This has worked for many years, but just as you say, its not the most efficient way of doing it. The fan usually robs about 15-20 HP. So removing the mechanical fan and putting in an electric one with a thermostat is better, but also costs a fraction more. This is most common on front steel drive cars with the transverse mounted engines.
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That's what I woulda thunk too. But, I'm in Southern California and we have already been well into the 90s and I've been stopped in traffic with the A/C on high.

Anything that won't break would be an improvement.
It isn't the engine speed that dictates the air flow, it's the ground speed. If the car is moving, there is air flow through the radiator, and if the A/C is on, there is an electric fan that kicks in, maybe this fan is enough ... Hmmm,
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Strictly speaking, no. It's the air speed only. However, we won't quibble for a motor car... :-)
For an aircraft it really matters whether there is a headwind or tailwind. The difference between ground speed and air speed can easily reach 50 mph or more.
DAS
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----- Original Message -----
Newsgroups: alt.autos.bmw Sent: Wednesday, July 06, 2005 2:16 AM Subject: Re: A funny thing happened on the way thru an oil change
snip

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.
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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.
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R. Mark Clayton wrote:

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

It would be difficult to have an engine driven fan that was between the engine and the radiator. If one didn't care where the fan was relative to where the radiator was, then it would be a relatively simple matter to have an engine driven fan. It wouldn't be a very useful fan though.
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Not so - the original Mini did just this. With a side mounted rad...

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Or a progressively driven mechanical one which idles when not needed...
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wrote:

The latest hi-tech zenith of efficiency is the Viscotronic fan. This has an engine management controlled variable speed viscous fan. It is an amazing piece of kit. I happen to have a bit of experience with an application where a diagnostic laptop can be linked to the vehicle and the speed of the fan can be infinitely varied within reason by means of mouse on slider. It so happens that I have two near identical vehicles except that one has a simple viscous coupled fan and the other having the latest viscotronic unit and the reduction of noise from the latter is very noticeable. With the same fan blades it is probable that this equates to a significant gaining of horsepower or reduction in fuel consumption.
Huw
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Huw wrote:

Cool beans...
That is the exact bit of trivial detail that had me asking the question in the first place. On my Z3, once the engine reaches full temperature, the fan noise at normal engine rpm (above 3000 rpm) is annoying, even though I'm tooling along at a high enough rate of speed so that the need for the fan is negligible.
-Fred W
PS - I'm just back from 2 weeks R&R in northern Maine, in case anyone missed me (or hoped I had dropped off the planet...)
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Dave Plowman (News) wrote:

err, but it DOES do just that.....
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;-)
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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spare-me-spam wrote:

No, it doesn't. The fan runs even when the car is moving forward at a high speed forcing more air through the radiator than the fan ever could.
-Fred W
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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.
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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.do?model 51&mospidG544&hg&fg5 for the main fan (located between the radiator and engine) and http://www.realoem.com/bmw/partgrp.do?model 51&mospidG544&hgd&fgU for the AC fan (located in front of the radiator).
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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.
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