I would like to convert the mechanical fan on a stock cooling system on my 1991 XJS V12 convertible, it runs right on temperature when I am on the freeway and have a lot of air flow, but in city traffic, now it is getting pretty warm here, the gauge gets a little too high for my liking. I was thinking I might have a dodgy fan clutch, but my mechanics think not, so it seems to me the best thing is to get a primary electric fan, my secondary electric fan comes on correctly. Everything else on the cooling system has been checked out, I would like to get this addressed before I eventually fix the A/C
geoff,
i fitted electrics fans to my XJ6, using a coil type temp sensor with temperature dial selection, it’s withing 2 -+ deg, you can get very good electric fans on ebay, just get the biggest that will fit comfortably, pic below is of the temp sensor and you can also set it up to run on after engine turn off to keep cooling. …where are you located?
It should not.
An electric fan might mask the problem but you should find the real cause.
Either your mechanic is wrong and the clutch is tired, air in the system, the rad is partially blocked, either internally or externally, you thermostats don’t fully close the bypass, internal blockages, etc etc.
First thing to do would be the easy stuff, remove the radiator and have it checked. You will have to remove it anyway if you want to fit an electric fan.
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Tom, I am located in Napa California, I have new thermostats and the cooling system has been drained and refilled and bled everything is clear on the radiator I do suspect the fan clutch, but would rather go the electric fan route
Are you referring to the space between the condenser coil and the radiator?
If not, that may be the cause.
At highway speeds, the air has enough umph behind it to force its way through leaves and debris, or is of sufficiently higher speed/greater amount of air flow to cool the part of the radiator which is exposed above the blockage.
However, at lesser speeds, cooling air flow through the radiator relies much more on the ability of the fans to pull the air through the radiator.
Geoff,
it’s easy to do, and as mentioned by others just make sure there’s no blockage with dust/leaves, you can use water or air to blast anything out. can you post here or send me a message with a side view picture of the fan setup you have, i’ve fitted after market fans to my own jag & 4 other cars of mine over time & well over a few 100 to customers cars when i was a mechanic full time…happy to help out if more info needed
Tom, there is no debris and the radiator, at least externally, looks in really good condition. I am wondering about the viscous fan clutch it spins freely when cold but should it lock up when the motor is hot? because mine does not. Mine is a completely stock cooling system with the exception of a replacement fan blade for the old yellow one, cheers Geoff
geoff,
i maybe stating something you already know so> does the fan match engine RPM when idling or does it look like it’s not engaging fully? the viscos fan should run at low speed when idling or low speed then increase as the RPM increases then slow after deceleration, the idea is to just run enough to maintain air flow without too much drag on the motor…but they are prone for all sorts of problems…temp/controlled electric fans are more efficient and less drag on the power/HP system…giving a bit more HP…
If viscous coupling for the fan isn’t new, just replace it. They are $50.
Robert, I think I will talk to my mechanic again and make a decision, just replace the viscous coupling or go the electric fan route. I do like the idea of the electric fans I have one pushing air on my Spitfire and it keeps at 180 degrees whatever the temperature is, much smaller motor though!
I have nothing against electric fans, but it is a lot cheaper and easier to replace the fan clutch. Plus with an electric fan you add another 25amp load on the alternator. Most modern cars with e-fans have 120-140amp alternators. You Jag doesn’t.
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The clutch needs replacing.
I will second Robert’s opinion, replacing the clutch will be the easiest.
If you go electric you will need to find the right fan, maybe modify the shroud, add a control system/relay and in the end you will discover that your Alternator can’t cope with the extra load.
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Robert, actually I have a 115 amp Bosch alternator on my car, but I am leaning towards just replacing the fan clutch, I will talk with my mechanic tomorrow and see what he says but as Aristides says I will have to find the right fan and modify the shroud as well, thanks to all, Geoff
Hi,
As stated: replace the clutch and in case you go aftermarket remember that all (yes all) viscous clutches are adjustable.
I went electric with my 6 cylinder XJSC for a very different reason, and that is a personal obsession with idle quality (getting rid of all rotating ancillaries that can be made redundant). Doing it really right is much more complex than a thermal switch, and involves a variable speed controller.
For my much larger Bentley Continental R with a Turbo i went temporarily electric, but even a massive triple fan set up with 36 Amps and high efficiency blades was only barely enough in South France, so i reverted to viscous, very carefully adjusted so that it would really kick in at 92C.
Heat release in the V12 after a nice highway run and into a jam can be massive. My guess is to keep viscous.
One last thing: in case your mechanic would not have the experience. You will need one sucker covering the cowl opening where the mechanic fan is, basically 550mm. In the US there are nice fans for V8’s that might give you the power you need. They will be rated a 24Amp continuous at least, but wire them with a single speed relay and you will get much higher start up currents. Believe me it does not feel nice. You can also go with two slim fans, diagonally installed and wired a different temperatures (91 and 93 C for example) that would give a stepped start using the usual fan relays. Spal has 355 mm super slims with rather quiet curved blades that MIGHT fit under the cowl. What you really want however is a PWM (pulse width modulated) controller.
Unless you really want to go electric and your mechanic really knows what he/she is doing, a properly adjusted viscous is the solution.
Well my mechanic is very experienced with British cars, he has done a ton of work on my Spitfire and it runs like a champ now, as well as a lot of work on the XJS, but everyone has convinced me to keep the mechanical fan so I have ordered a new fan clutch from Moss Motors, together with a nice Jaguar beanie! Thanks for all the help, cheers Geoff
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Where?
I’m in Roussillon in the Vaucluse.
Yes, yearly. I really noticed that the electric set up struggled, not in jams around Narbonne, but on the long and lorry-slowed ascents through Millaud and La Jonquera.
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PS: struggled meaning the needle would move from the middle range, not that the car over heated.
Follow up to my worry of overheating, I have had a new fan clutch installed, the motor makes a little more noise now but I notice the fan is a lot stiffer with the new clutch, before it would spin quite freely also the temp needle now sits exactly in line with the top of the N mark on the gauge which my mechanics told me they measured at 190 F, which seems correct as I have 188 F thermostats, so hopefully all is good now, if not next step is new radiator.
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