Hey guys


I am trying to find a good and relatively easy solution to a problem a lot of people with mechanical fans have in extreme heat climates. My AJ16 XJS can't keep up once she's been sitting in traffic for 20/30 minutes or more. The A/C stops cooling properly and the needle starts going up. Obviously a mechanical fan turning at very low RPM's can not do what a powerful electric fans can do in this type of situation.

I think the XK8 fans might be an easy fit for my car, but I am curious if the member here think the fans are powerful enough, or if I should look for a later model. Also, what would I need to buy along with the fan to make it work as intended? Do your cars have a module that regulates speed?

Any help greatly appreciated

 

I have experience in both of these cars for what it's worth.

Do you know if the fan clutch has any resistance when you try to turn the fan by hand? Also, do you know if your electric cooling fan is working?

We have installed one of these kits on a customers V12 XJS and it worked great.
http://www.v12performance.com/CatCooler.html

I know what you mean by the A/C not working well. We just had an original owner with a 1995 XJS 6 cylinder with 55k miles come to us about 4 months ago with the same issue. We ended up putting in a new higher effiecient condensor and he was super happy.

 

Thanks for your reply.

The XJS has a modern parallel flow condenser fitted to it as well as a couple of small pusher fans fitted to the front of the condenser. Cooling system has all been redone right down to the cowl and clutch where the main mechanical fan go. It all goes great until it's been over 20 minutes in stop and go traffic in 100 plus degree heat. Replacing the main mechanical fan is the next step.

I am pretty sure I can fit the XK8 fans in there, I am just not sure as to what controls them and if they are considered particularly efficient

 

Hi,

the fans have a control module which is controlled by the ECM (engine control module) The XK8 XJR have 2 fans. the Jag system runs them in series for low speed (probably for noise) and parallel for high speed. My XJR fan module died and I have been messing with the fans. I live in Florida so it is hot. If I run 1 fan at full speed the temp never exceeds 195 unless I get it on boost. Even if I leg it out it might go to 205 but comes right back down with 1 fan. I am ditching the Jag fan module and adding 2 fan controls from Jegs.com I am setting one to turn on 1 fan at 185 deg and the second will come on at 205.
The thing I really like about this setup is if one fan relay quits the other will still work and the engine won't overheat. Fuse each relay separately 30A fuses.

 

Clutching fans suck (or don't suck enough). The XK8 fans are excellent, but there are other junkyard dual/single electric fan setups that might work, too.

What are the dimensions of your radiator and how much room would you have from the radiator to the motor with the clutching fan removed?

Series/parallel fan wiring isn't too hard to do with relays. To make a circuit, you just need to know the trigger signals for fans on and low/high or trigger it yourself. When the fans run in series (low speed), its not only quiet, but they only draw about 5 amps, vs. 30 when they switch to parallel (high speed).

 

Lots of people in the classic car world fit one of these, Kenlowe Retrofit Engine Cooling Fans

 

Thanks so much for your replies

I have decided to go with a 97-02 XK8 fan for sure. I took one of my cars to my Jaguar specialist and he said he thinks the XK8 fans are probably the best fit for my XJS .

Couple more questions:

All the XK8 fans look alike to me but they seem to have different part numbers depending on if the car is supercharged or not... Are all these fans the same? Or are the SC model fans more powerful in some way?

Also, are your alternators rated at 120amps? I am thinking of getting a new alternator as well to keep up with the fans

Thanks!!

 

Beyond the physical installation you are going to have to build a control system. The OEM XK8/R installation is managed by the ECM through the fan control module based on resistance input from the temperature sensor. The ECM/FCM run the fans in series at lower engine temperatures and in parallel at higher temps.

Since your car has nothing like that available for you to attach to you will need a complete system to manage the fans. I am not sure what your, or your technician, have in mind for such a system but here is what I did when doing some 'hot rodding'.

Turbobricks Forums - View Single Post - Volvo's That Run Chapter 18 Radiator, Hoses, Fan and Heater Hoses

 

Has your specialist actually measured up fans verses space available on the xjs? I have ford falcon fans on my xjrs. They just fit in space available between front of motor and radiator and they are lower profile than xkr fans.

 

Because dual motor Series/Parallel 12V is how a Power Wheels ride-on Toy switches from Low Speed to High Speed, I can post the diagrams for the circuit. It takes two DPDT 30/40 amp relays and another Relay to turn the fans off/on. Another relay may be needed depending on if the High/Low signal is "ground" or "12V+"


Basically with 3 $5 Relays and a $20 fan controller thermostat off Amazon, the fans can come on low speed with the key (about 5 amp draw) and only switch to high speed when temps reach a predetermined set point.


In high speed, if one of the fans goes out, the other will still work. Both won't work in low speed if one fan is bad, but when it heats up and switches to high speed, at least one fan will still work.

 

Thanks everyone for your replies.

I wonder if it's possible to control the OEM XK8 fan module directly from a thermostatic switch and bypass the ECU? I had though of using a SPAL fan controller , but everything OEM sounds better to me. I've had too many AM parts not work as they should in the past.

While I intend to buy any harnesses or fan module (if I do decide to do that) from a wrecked car, I WILL BE BUYING THE FANS NEW. There is a considerable price difference between the SC fans and the non SC FANS. They look the same, but the SC fans are cheaper.

Thanks !!

 

Anything is possible . . . but . . . you will have to start out with a radiator mounted temperature sensor or find a blank NPT hole in the block. All sensors I am aware of are simple varistor based devices that convert temperature to resistance. Now you will have to convert the resistance into relay control. Not sure how you would do that conversion into the series/parallel operation of the OEM fan control module without some intelligence like the OEM ECM. Not aware of a stand alone device with that capability.

There are a number of controller designs available using relays but they all seem to be on/off operation. My opinion is that the current regulated fan control is far superior to relay on/off operation and even the series/parallel Jaguar design.

 

The Jag switch uses PWM to control it. You would need to make an electronic circuit to change the temp senders resistance (which would be variable voltage) to Pulse width modulation (which is duty cycle) In my opinion the easiest and most bulletproof way to do it is as I mentioned in an earlier post. There was a recent post which presented a similar approach. His approach has the flaw of always having fans on with the ignition. Sometime you may encounter cold weather and not want any fans so your heater works better. My solution uses dual thermostatic relays so it is redundant and is most like the factory setup on the cheap without overly complicating things with electronics like Jag did.

 

I would like to understand how the control system you describe works. Got a link to a post with more details or part numbers/sources and schematic?

To the best of my knowledge the '97 - '02 XK8/R and '98 - '03 XJ8/R all used DC control of the fan control module to turn the fans on either in series for low speed or in parallel for high speed. The later models may well have had PWM to control the fan speed as did the later fuel pumps.

 

There may be a danger of the discussion getting too set on the switching mechanism of a fan set up before it is even fitted to the car.
The xkr fan assembly depth from radiator is about 110mm measured at the LHS fan right about where the lower elbow and thermo switch is on the XJS and there is a good chance fouling will occur in that area.
My fan switch on my XJRS is in the radiator and l used a non switch version of the lower elbow because of that problem in the mounting of ford electrics.

 

Thanks for your reply. My car is a straight 6. There seems to be ample space there for a fan once I take the huge cowl out

 

Sorry, l missed that bit in your original post.

 

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.

 

Here is a link to the thermostatic relay that I am using. The temp dial is not accurate so measure using a scan tool or a pot of water on the stove with a thermometer or your temp gauge if it is accurate.

Speedmaster PCE184.1005: Adjustable Electric Thermo Fan Switch Kit 12V | JEGS

 

Thanks everyone for your help. It looks like the XK8 fans don't come with any wires, so whatever system I am going to use I will need part of the harness with the connectors. Also it looks like a two wire connector goes into each fan