Why a water cooled alternator?

[verite]

Lots of other cars get by fine with a regular alternator.

Why would BMW opt for such an expensive design?

Just curious, as I'm sure many of us have had to swap these complex and pricey pieces out.

[zM3]

Alternators, like other electrical equipment, need to be protected from heat to survive and operate efficiently. Alternators have integral fans that help with cooling but still require airflow of sufficiently low temperature for heat transfer. Some cars (at least one 4 cylinder Ford/Mazda engine I've seen, for example) have a duct which directs air from the grille down to the alternator for cooling. Everything in a car design is about optimizing different attributes - choosing water cooling is expensive and complex but may provide more flexibility in where the alternator is placed on the engine and probably provides more cooling than just air, and that may enable a higher rated (power) alternator to be used. It may also enable other positive tradeoffs to be made (styling, engine power, etc) that result in higher underhood temperatures but won't kill the alternator.

[verite]

Thanks! Great answer.

[bullard123]

And from my understanding only the v8 models have one

[JimLev]

They didn't want to use the pulley mounted fan because of noise concerns. I really don't remember air cooled alternators being noisy.
The tu alternators were 150 amp 3 phase units with no brushes or slip rings.
So without air for cooling, water was used which was suppose to keep it at a constant temp. Is that lower or higher than the air cooled units that have a cooling duct?

For the E39 models only the V8 tu engines got them.

[Arctikz]

The alternators are tucked to far down to be cooled adequetly by the small amount of airflow that the duct system found on the non vanos m62 provides. The water cooled alternators will last must longer and i beleive run at a higher amperage then the ones on the pre 98 cars which is the reason water cooling was choosen. Though i definently prefer the non-water cooled alternator when it comes to replacing it. BMW redid the entire cooling system after 98 and the water cooled alternator must have gotten into an engineers mind and they decided to make it a reality. After all, the e39 was designed by the japanese.

[verite]

http://www.allpar.com/eek/alternators.html

[Guam135i]

interesting

[TriniSpeC]

why plastic timing chain guide rails?

[jaym540i]

why plastic timing chain guide rails?

plastic timing chain guides have been in common engine building use for quite some time. They keep things quiet. The other alternative is a timing belt and i would much rather have the chain as opposed to the belt.

[TjGonzo]

and here I thought it was just a way to rape us for parts and repairs later on....

[JimLev]

and here I thought it was just a way to rape us for parts and repairs later on....

Bingo! hit the nail on the head.

[carlos1212]

Don't forget about the 97-98 540's, those came with air cooled alternators. and don't really have problems.

to me it seems stupid BMW would go water cooled

[kysteezy]

Don't forget about the 97-98 540's, those came with air cooled alternators. and don't really have problems.

to me it seems stupid BMW would go water cooled

It was explained up there more^^^

[carlos1212]

It was explained up there more^^^

sorry, how the hell did I miss that? I was pretty sure I read the entire thread before posting

Also, are water alternators really more reliable? in the 3 years that Ive been on this forum Ive seen more threads on water cooled alternators

[Random77]

sorry, how the hell did I miss that? I was pretty sure I read the entire thread before posting

Also, are water alternators really more reliable? in the 3 years that Ive been on this forum Ive seen more threads on water cooled alternators

You probably see a lot of threads on water cooled alternators, since there are a lot of people with '99-'03 540s on here. There was a poll on here recently that asked what model e39 members have and about 53% have a 540i and only 2 years of production have the air cooled alternator on the 540i. http://forums.bimmerforums.com/forum...highlight=poll

Most people have never seen a water cooled alternator before, so there are a lot more questions about it. It's also notable when it fails, since it costs a lot more than the air cooled alternator.

[verite]

It's also notable when it fails, since it costs a lot more than the air cooled alternator.

Ya, when I first looked up the price for one, I thought it was a typo.

[webdesigner]

why plastic timing chain guide rails?

You can't use metal

Plastic composites have come a very long way, there's a lot of engineering involved

Plus, this tends to only happen after 100K.

BMW does not care about cars past their lifetime, i.e. 100K miles.

I mean hell, I bought a $65,000 car for $18,000? I could care less about a couple thousand in repairs.

[bmb527]

You can use metal, some manufacturers did use metal. One main issue with it though is noise. it makes plenty. Another is wear. The metal used in guides is softer than the chain, so it wears just as a plastic one does. The metal ones don't last even as long as the newer plastic parts do! With the technological advances in composite materials in the last few years, plastic is certainly the best way to go.

[motion]

Don't forget about the 97-98 540's, those came with air cooled alternators. and don't really have problems.

to me it seems stupid BMW would go water cooled

When i purchased my 540 the alternator cooling ducts from the front valance back was totally impacted withe leaves and debris.

[TriniSpeC]

and here I thought it was just a way to rape us for parts and repairs later on....

yeap. everything has a expiration

[514mach1]

The correct phrase is, "I couldn't care less", as in you could not possibly care less because you don't care at all. Back in the '50s it was expounded upon by some with the statement, "I suppose I could care less, but I don't possibly see how." That may be where the confusion comes from, but I think it's more likely an issue of people not hearing the end of "couldn't" and it's stuck.

Anyway, the water cooled unit may well have been done to reduce noise. I see no other logical purpose for it. To me, it's way too expensive and BS-ish to justify. My '97 has the ORIGINAL air cooled alternator at 230K miles. I got my car from the original owner who kept ALL the receipts from oil changes to radiators and motor mounts. I even dug into the alternator a bit while I was doing the timing chain guide job. The bearings were smooth and the brushes had only a little life left. The slip ring is also pretty worn. I've got a new brush/regulator in the garage and should get a slip ring and bearings to rebuild it some convenient fair weather day.

And my alternator duct was full of leaves and sand also.

[rf900rkw]

Everyone seems to be focusing on why they put a water alternator in the E39. A better way to look at it would be why they put a water cooled alternator on the M62. Was there a need or justification somewhere else and they just made an across the board change? Environment-proofing for the X5? Higher output for the police/rescue/limo package? We can only guess. But I'm quite confident the reason was NOT just to screw the third-hand owner 15 years hence.

[TriniSpeC]

Everyone seems to be focusing on why they put a water alternator in the E39. A better way to look at it would be why they put a water cooled alternator on the M62. Was there a need or justification somewhere else and they just made an across the board change? Environment-proofing for the X5? Higher output for the police/rescue/limo package? We can only guess. But I'm quite confident the reason was NOT just to screw the third-hand owner 15 years hence.

everything has a purpose, the alternator is mounted low in the block, or well the timing cover, a water cooled unit was perhaps the only way to keep it from overheating. Im not mad.

[edjack]

The water-cooled alt was a German wet dream, as was the use of probably the worst tire ever: the Michelin TRX.

Note that subsequent V8 Finfers do not, AFAIK, have a water-cooled alt.