XJS owner needs help- XK8 fans
#21
09-24-2016, 11:05 AM
Join Date: Apr 2011
Location: Galleria Area Houston, Texas
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Most early cars with electric fans just have a thermostatic switch that screws into the radiator. when the water reaches a certain temp the fan turns on. When it cools down it turns off. This is simple , effective and has worked well for a long time. The downside is you may hear the fan come on. PWM or pulse width modulation is using a micro processor to turn a voltage on and off frequently which limits current. An on off switch is 100 percent duty cycle when on. So if you take 1 second which is equal to 1000 milliseconds and you use a micro controller to switch the voltage on and off rapidly so that the on time is 1/2 of a second or 500 milliseconds you have limited the current to the fans. This would be a 50% duty cycle. Jaguar also wires the fans in series. The combination of the two allows the for a number of things such as soft starting and the ability to control fan speed. Air conditioning compressors are also controlled this way in modern cars instead of the old on / off clutch mechanism. For A/C there is a significant benefit to this method of control. As far as fans go I personally would rather have rock solid dependability.
This kit is complete.
Painless Electric Adjustable Fan Thermostat Kits | JEGS High Performance
You can piece it together for less at Jegs. I purchased 2 thermostatic switches for 10$ ea and 2 30A relays at advance auto for about 10$ ea. My XJR already has 2 fused circuits , one for each fan.
The wiring is as follows:
power from the fuse block goes to one terminal of the thermostatic switch and to one terminal of the fan. This will be ground side switching which makes the relay last longer.
the other fan wire goes to one switched terminal of the 30A power relay.
The other switched terminal of the power relay is connected to chassis ground.
The two remaining terminals on the power relay control the activation of the relay. connect one of these wires to the remaining terminal on the thermostatic switch and connect the other terminal to chassis ground.
The thermostatic switch has a sensor bulb that needs to be placed in the radiator it also has a dial that is used to adjust the on temperature. adjust the temperature using that dial to the desired fan on temperature.
In my XJR I used 2 of these systems, 1 for each fan. the first activates at 180 degrees the second activates at 205 degrees F. This works very well, it lets you see if the fans are working from the temp guage. If the temp goes straight to 205 then there is a problem with the primary fan system and the secondary fan will prevent an overheating situation. If the temp stays steady in the 190's all is well. If you go somewhere cold, no fans, nice heat. It is redundant there isn't one thing like loss of the PWM signal or the combination relay which will leave you with no fans and the possibility of a ruined engine.
This kit is complete.
Painless Electric Adjustable Fan Thermostat Kits | JEGS High Performance
You can piece it together for less at Jegs. I purchased 2 thermostatic switches for 10$ ea and 2 30A relays at advance auto for about 10$ ea. My XJR already has 2 fused circuits , one for each fan.
The wiring is as follows:
power from the fuse block goes to one terminal of the thermostatic switch and to one terminal of the fan. This will be ground side switching which makes the relay last longer.
the other fan wire goes to one switched terminal of the 30A power relay.
The other switched terminal of the power relay is connected to chassis ground.
The two remaining terminals on the power relay control the activation of the relay. connect one of these wires to the remaining terminal on the thermostatic switch and connect the other terminal to chassis ground.
The thermostatic switch has a sensor bulb that needs to be placed in the radiator it also has a dial that is used to adjust the on temperature. adjust the temperature using that dial to the desired fan on temperature.
In my XJR I used 2 of these systems, 1 for each fan. the first activates at 180 degrees the second activates at 205 degrees F. This works very well, it lets you see if the fans are working from the temp guage. If the temp goes straight to 205 then there is a problem with the primary fan system and the secondary fan will prevent an overheating situation. If the temp stays steady in the 190's all is well. If you go somewhere cold, no fans, nice heat. It is redundant there isn't one thing like loss of the PWM signal or the combination relay which will leave you with no fans and the possibility of a ruined engine.
#22
09-25-2016, 03:12 PM
Member
I have chosen not to run both fans at different speeds for a few reasons.
( I run each fan at different temperatures so the fans will either be off, 1 on or 2 on depending on the engine temperature )
1) when you run the fans in series for low speed. You are wearing both fans, if one fan quits , they both quit because they are in series (like those old christmas lights that drove everyone nuts when a light burned out)
2) as I mentioned before the system I outlined is bulletproof.
3) I don't hear the fans in my XJR so slow speed operation is just something A jaguar engineer did to be ridiculous and keep you going to the dealership for service. In my opinion.
Either way you decide to go all you need is the 4 wires that you have.
Since your ECM does not have a PWM out signal if you want the fans to work exactly as Jag set them up. You will have to program a microcontroller Pic, arduino etc and make a circuit which includes a transistor to output a PWM signal. Then you will need the Jag relay $140 and the wiring harness (i think it is the front marker light harness ) who knows 100 bucks? and then a few hundred for someone to make a PWM board. Or for around 70 dollars you can do it as outlined and be able to maintain it yourself.
( I run each fan at different temperatures so the fans will either be off, 1 on or 2 on depending on the engine temperature )
1) when you run the fans in series for low speed. You are wearing both fans, if one fan quits , they both quit because they are in series (like those old christmas lights that drove everyone nuts when a light burned out)
2) as I mentioned before the system I outlined is bulletproof.
3) I don't hear the fans in my XJR so slow speed operation is just something A jaguar engineer did to be ridiculous and keep you going to the dealership for service. In my opinion.
Either way you decide to go all you need is the 4 wires that you have.
Since your ECM does not have a PWM out signal if you want the fans to work exactly as Jag set them up. You will have to program a microcontroller Pic, arduino etc and make a circuit which includes a transistor to output a PWM signal. Then you will need the Jag relay $140 and the wiring harness (i think it is the front marker light harness ) who knows 100 bucks? and then a few hundred for someone to make a PWM board. Or for around 70 dollars you can do it as outlined and be able to maintain it yourself.
#23
09-25-2016, 03:55 PM
Veteran Member
Any number of control systems to chose from for one fan or two.
https://www.summitracing.com/search/...radiator-probe
All use either a radiator mounted thermistor sensor or one mounted in a spare hole in the engine water jacket.
Not rocket surgery.
https://www.summitracing.com/search/...radiator-probe
All use either a radiator mounted thermistor sensor or one mounted in a spare hole in the engine water jacket.
Not rocket surgery.
#24
09-25-2016, 06:38 PM
Sponsor
Fan control.......
You know, there is nothing exotic about the fan control box on an XK8 or XJ8- it is just 3 standard relays together in one unit, offering the high and low speed as you mentioned. On the conversions we do, GM does it exactly the same way except that the relays are standard $6.99 units plugged into a larger relay box.
If you want, PM me offline and I can send you the wiring diagram and the number of a standard Bosch mini relay that could be used in such an application. Those relays are about $6 each. And in the case of your V12, there is a way to set it up so your AC might turn the fans on at low speed and then the thermal switch to override it should engine temps get to a preset level (and go to high speed....)
BTW- from a physical basis, I doubt an XK8 fan set would fit an XJS application- I believe it's too wide. I have both cars here- I'm pretty sure on this. Another more reasonable possibility (which is the correct size for an XJS radiator opening) is a fan set (fans and shroud) from a 98-02 Camaro with the LS1 engine. They pull a ton of air, are very reliable, and Dorman sells the complete assembly brand new for only $100.......
I hope that helps
Andrew
Jaguar Specialties
If you want, PM me offline and I can send you the wiring diagram and the number of a standard Bosch mini relay that could be used in such an application. Those relays are about $6 each. And in the case of your V12, there is a way to set it up so your AC might turn the fans on at low speed and then the thermal switch to override it should engine temps get to a preset level (and go to high speed....)
BTW- from a physical basis, I doubt an XK8 fan set would fit an XJS application- I believe it's too wide. I have both cars here- I'm pretty sure on this. Another more reasonable possibility (which is the correct size for an XJS radiator opening) is a fan set (fans and shroud) from a 98-02 Camaro with the LS1 engine. They pull a ton of air, are very reliable, and Dorman sells the complete assembly brand new for only $100.......
I hope that helps
Andrew
Jaguar Specialties
Last edited by JaguarSpecialties; 09-25-2016 at 08:48 PM.
#25
09-26-2016, 12:27 AM
BTW- from a physical basis, I doubt an XK8 fan set would fit an XJS application- I believe it's too wide. I have both cars here- I'm pretty sure on this. Another more reasonable possibility (which is the correct size for an XJS radiator opening) is a fan set (fans and shroud) from a 98-02 Camaro with the LS1 engine. They pull a ton of air, are very reliable, and Dorman sells the complete assembly brand new for only $100.......
I hope that helps
Andrew
Jaguar Specialties
Last edited by baxtor; 09-26-2016 at 12:48 AM.
#26
09-26-2016, 08:59 AM
Sponsor
Interesting
Interesting-
You know, I went out just now and measured an XK8 shroud and you're right- it's not too wide. It actually comes out a little narrow and a little short in height. I guess I had in my mind when I compared it originally to an XJ8 fan/shrouid set a while back, which is tall and narrow- made the XK8 piece look very wide. Regardless, it's likely not a great choice for an XJS application as it's designed to bolt to the radiator tanks (not simple to integrate onto a brass style radiator that has no such provisions), besides the size mismatch. And that doesn't even get into the cost of such a unit.
Isn't there a company that already makes an electric fan set and shroud for the V12 models?? I've seen their ads from time to time.
You know, I went out just now and measured an XK8 shroud and you're right- it's not too wide. It actually comes out a little narrow and a little short in height. I guess I had in my mind when I compared it originally to an XJ8 fan/shrouid set a while back, which is tall and narrow- made the XK8 piece look very wide. Regardless, it's likely not a great choice for an XJS application as it's designed to bolt to the radiator tanks (not simple to integrate onto a brass style radiator that has no such provisions), besides the size mismatch. And that doesn't even get into the cost of such a unit.
Isn't there a company that already makes an electric fan set and shroud for the V12 models?? I've seen their ads from time to time.
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Spikepaga (09-26-2016)
#27
09-26-2016, 10:01 AM
Join Date: Apr 2011
Location: Galleria Area Houston, Texas
Posts: 2,925
Received 552 Likes
on
377 Posts
Interesting-
You know, I went out just now and measured an XK8 shroud and you're right- it's not too wide. It actually comes out a little narrow and a little short in height. I guess I had in my mind when I compared it originally to an XJ8 fan/shrouid set a while back, which is tall and narrow- made the XK8 piece look very wide. Regardless, it's likely not a great choice for an XJS application as it's designed to bolt to the radiator tanks (not simple to integrate onto a brass style radiator that has no such provisions), besides the size mismatch. And that doesn't even get into the cost of such a unit.
Isn't there a company that already makes an electric fan set and shroud for the V12 models?? I've seen their ads from time to time.
You know, I went out just now and measured an XK8 shroud and you're right- it's not too wide. It actually comes out a little narrow and a little short in height. I guess I had in my mind when I compared it originally to an XJ8 fan/shrouid set a while back, which is tall and narrow- made the XK8 piece look very wide. Regardless, it's likely not a great choice for an XJS application as it's designed to bolt to the radiator tanks (not simple to integrate onto a brass style radiator that has no such provisions), besides the size mismatch. And that doesn't even get into the cost of such a unit.
Isn't there a company that already makes an electric fan set and shroud for the V12 models?? I've seen their ads from time to time.
#28
09-28-2016, 08:24 AM
Sponsor
XJS 6 cyl
In that case you might want to take a close look at the either the 94-97 Camaro LT1 twin fans/shroud assembly or the slightly different 98-02 Camaro LS1 version. Either of them should be a decent fit with the correct height. And either one will be more reliable and less expensive than the Jaguar XK8 piece....
#29
09-29-2016, 12:11 PM
Veteran Member
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