Does anyone know why Jag used the engine-driven fan (+additional electric) rather than electric only (eg E-type) for the XJ12 and XJ-S?
It seems to me that the all electric system is superior
Figuring out the âwhy?â of Jaguar decisions can sometimes be entertaining and amusing. Or, annoying. Jaguar tended to cling to existing ideas and technology long after others moved on. In many cases it comes down to saving money.
The mechanical fan got the job done so I guess they decided to spend money elsewhere.
Always remember that there are no design flaws on a Jaguar. Anything appearing to be a design flaw is actually an âinteresting engineering featureâ 
Cheers
DD
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I understand they had reliability issues with the electric fans on the SIII E-Type. Most companies can build a reliable electric fan, but Jaguar/Lucas seemed to have trouble with it. So they might have switched to a belt-driven fan just to rid themselves of a headache.
Since weâre pondering Jaguar rationale, why have both a mechanical fan and an electric auxiliary fan? Why not a bigger mechanical fan capable of doing the job, sans the auxiliary?
Packaging/available space?
Noise?
Anyhow, Jaguar spent the money where they thought it would do the most good, sometimes foolishly. Gorgeous wood, leather, and chrome, yes. But think of how Jaguarâs reputation wouldâve been enhanced by usingâŚgasp⌠sealed electrical connectors?
Or $1.50 window switches in place of the 89-cent switches?
Cheers
DD
The engine driven fan is cheaper and uses zero amps. It covers basic cooling needs. It is too small for hot days in traffic but uses less power and is mostly adequate.
The second fan does the rest. Many cars are like that⌠and two fans are a better package.
One of the two will keep running if something fails. Some 90s BMWs are the same way so itâs not âJaguar being old fashionedâ. Cheap switchgear ruins car and reputation - but twin fans are better than one monster of a fan.
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I changed to a Davis Craig 16 inch electric main fan and the first thing I noted was the increase in noise compared to the mechanical fan. To the point where I fitted a pulse wave modulator. I now only run the fan at 100% in the middle of summer. Going from 100-75% fan speed reduces the under bonnet roar dramatically. Jaguar valued their cars a quiet an sophisticated⌠perhaps thatâs why they stayed mechanical.
I dunno about Davis Craig, but most electric fans are pretty quiet. Their sound is quite noticeable, though, because 1) it runs at full blast even if the engine is idling, whereas the belt-driven would be barely moving any air at that speed; and 2) the electric fan speed doesnât vary with engine speed, so it canât be confused as just part of the engine sound.
Ok - that makes more sense than the âsticking to old technologyâ argument- after all they had to design and troubleshoot new parts to fit the mechanical fan.
I note also the comment about noise, but i have never felt that the e-type fan (or those on a Jensen or BA Falcon) were offensive
What new parts? Jaguar (and others) had been using mechanical fans sinceâŚforever. For ages that was the norm.
Seems to me the question, though IMO thoroughly academic decades on, is why they continued using them for so long, when others were transitioning to e-fans?
Maybe they felt the mechanical fan worked better? Perhaps so; perhaps e-fans of sufficient capacity were not reasonably available when the XJS was being designed?
Maybe they didnât want to contend with the increased electrical demands?
I dunno.
More fodder for speculation:
Why did Jaguar cling to the TH400 transmission long after it was obsolete?
Why did Jaguar continue using non-sealed electrical connectors in areas exposed to the elements when sealed connectors were readily available?
Why did Jaguar insist on using, for decades, ridiculously complex transmission mounts when much more simple designs worked equally as well?
Adherence to tradition? âWeâve always done it this way.â
Contractual obligations with suppliers?
I surely donât know!
Cheers
DD
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The Davis Craig fans (16 inch main + 12 inch aux) werenât so noisy on the bench mounted in the cowl. However fitted in the car its a different matter. I figure its that the fan is so close to the engine that the air roar is notable. But thatâs at 100% and I mostly run on 75% speed (PWM adjustment) but if I know I will end up in town on a very hot day (I live in the bush) I will set the fan at 100%. I can drive along the highway at 50% with no noticeable temp difference on a 25-30 C day but in town she will run warmer than usual at that setting.
Iâm thinking of mounting the PWM (on the under the bonnet currently) on the dash board but that doesnât solve the problem of noise as on the highway you canât detect any fan noise (at 100%) but in traffic at slow speed you can but thatâs when the fan needs to run on high.
If I were to run the electric fan proportional to revs (like a mechanical fan) it would be more inclined to overheat in heavy slow moving traffic much the way Jags do.
Itâs been my impression that GM stuck with belt-driven fans forever, only switching to electric fans for cars with transverse-mounted engines or other arrangements that would make a belt-driven fan problematic.
They began slowly phasing-in the e-fans on RWD cars in the mid 80s. Camaro Z28s, for example. But, yeah, I donât think they ever completely got rid of 'em.
Cheers
DD
My 2006 Range Rover with the Jaguar AJ41 gasoline 4.4 V8 EFI engine (variable cam timing, highly complicated fuelling system, etc etc) also uses a viscus coupling mechanical fanâŚ
My 1990 Mercedes as well.
There must be a reason.
I did the E-fan conversion⌠didnât like it⌠too much noise. Reverted back to the original setup.
AccountantsâŚ
Because they totally isolate the transmission from the body.
I canât see how a rubber mount can do that.
Iâd kinda like to see a design halfway in between: A spring to carry the weight and a rubber mount to control motion. The rubber mount, not having to support the weight of the transmission, would last longer and remain more flexible rather than getting squished. Do away with that silly spool and rounded edge washer scheme.
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You reminded me of my 1962 Morris Mini. It had a transverse engine and the radiator was mounted to the LHS fender well. Air would come through the grille, and then be pushed out through the radiator, sideways, using a belt driven fan. Pretty clever, really.
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Indeed it canât. But a butter-smooth driver experience doesnât require total isolation. The big American luxury land yachts were revered for smoothnessâŚand used a big chunk of rubber.
Thatâs money that couldâve been better spent on those sealed connectors ! 
Cheers
DD
The new parts are the fan bearing mounting and tensioner that needed to be fitted to the v12.
The E-type didnât have these parts.
Although there were other Jag vehicles with belt driven fans, the V12 was (as always) a special case
It wasnât a case of not introducing a new idea- it was a deliberate re-design, involving new systems and parts
As for the power of the fans, the E-Type, Jensen Interceptor and other large displacement cars of the same or earlier era had effective electric fans
Ah yes. Forgot about those.
Oh well, I suspect this will go down as just another Jaguar âwhy?â mystery.
Cheers
DD
Not a Jaguar mystery if it was done that way in the 80s and 90s. E38 BMWs have an electric pusher and mechanical puller. Same with Range Rover and Mercedes.
My guess is that it saves electrical power and money. The noise of a fan might help against engine noises and it could even be lighter.
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Iâm perfectly happy with âIndustrywide normâ as an explanation
Cheers
DD
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