1990 Jaguar XJS V12 145k

The cooling of my xjs has been mediocre at best and only acceptable after abit of maintenance. Never much of an issue driving on open roads or in the winter, but the car did not like stoplights, restarts after sitting a few minutes, or traffic.

I wanted to focus on the fans and airflow over the engine as the relays for the 12v fan were in poor shape and required manual switching after being messed with by a previous owner. I decided the solution was to use an arduino and new relay as the fan controller and add 4 120mm nidec server fans. The Arduino controls the relay with a new added temp sensor and scales the speed of the server fans accordingly.

The added fans are brushless 3.3a fans from computer servers and they move alot of air. I would estimate they are significantly more efficient then automobile fans for the 13.2a they draw. They fit well directly in front of the radiator, able to freely draw in air from the grill, you can feel a noticeable amount of air being pulled through the grill with the hood closed and the hood shape pretty effectively muffles the noise of these fans. I also replaced the mechanical fan clutch.

This upgrade nearly eliminated the issue of sitting in traffic or drive throughs, and now it is possible to leave the fans on for abit after shutting the car down to combat heatsoak, much like a modern car does.

 

I strongly suggest you look at cleaning between the radiator and the A/C condenser as well. All kinds of road debris including leaves collect and get trapped in there significantly restriciting air flow across the radiator. This is likely why when you are in traffic you have cooling issues.
As designed the system is adequate for the XJS. If the airflow is less than optimal then you will have temperature control issues.

 

Nice one OP! So the fans are PWM controlled by the arduono- is there a separate power control circuit for the fans?

You probably know but computer fans aren't rated for getting water spray etc in them, so they might not last well if you drive in the rain. You can get smaller radiator fans fitted to radiators of superbikes etc that might be suitable- IIRC these are 160mm or so.

I went the full way and just removed the engine driven fan and shroud completely, and fitted dual electric fans in place. Its a good upgrade.
Mine run on a soft start controller permanently at around 40% speed, with a 12v temp controller switching them to 100% speed when needed.

 

I love the ingenuity and bricolage! Well done! I wish that I were as handy as you've shown!

I went for a completely new system: new aluminium radiator, two Spal electric fans, new controller, new shroud, new hoses... even a new expansion bottle. All from NAR in England.

 

There isn't any significant debris between the radiator and the A/C condenser. Although the rad certainly isn't as clean as it could be, and ive only replaced the coolant, not thoroughly flushed it. The front air dam is also missing, ive been meaning to craft a new one out of carbon fiber.

I hear a few comments on how the cooling is adequate on these XJS, but I would call it subpar by modern standards. Its asking alot of a single mediocre electric fan to deal with the toast of the v12 in certain traffic conditions, especially on a xjs with 145k. Explains why there is such a focus on maintenance as well as modifications from owners. This upgrade came from the necessity to replace the current fan control electronics, I also saw the gap on the fount of the rad which wasn't suitable for most automotive fans but could easily house some of the server fans I had lying around.

The power draw for the fans is on a separate hot wire of sufficient gauge darefully procured by the po and left alone by me. The adruino is on a 12v switched ignition circuit. It switches the relay on at a specified temp and scales the pwm of the computer fans accordingly.

Im not too worried about the robustness of the fans, they are relatively sealed and could probably suck some water without harm. I like these fans as they are designed for high CFM, high static pressure applications making them great for a push fan on a radiator. They also have built in ducting to straighten the airflow and improve the efficacy. Plus they were sitting unused in my spare part bin.

 

So an important part of the cooling system is actually missing?

You might find this enlightening:

https://www.jaguarforums.com/forum/x...erence-213522/

Ignore the threadjack after the first couple of posts. The chin spoiler is a very important part of the overall cooling system.

 

The V12 XJS needs both the chin spoiler and the undertray for the cooling system to be up to snuff.

FWIW, I do not believe placing a row of fans in front of the radiator stack is a good solution to any overheating problems the car may have. Now, do not get me wrong, I love innovative ideas; but the problem of cooling is much more about addressing the airflow through the rad stack than anything else. If you have not had the radiator out, then you should do so and be 100% sure the airflow through the radiator, oil cooler and condenser is unobstructed. The radiator core needs to be in top condition too, and the thermostst replaced with ones known to be correct in their opening depth as well as working properly.
Next, if you have not done so, replacing the viscous fan hub is important, and replacing the old electric fan with a modern one, which should be wired to come on with the aircon.
If your car is a Lucas igntion one, then moving the secondary coil out of the airflow, and also the horns, is a big advantage. You can even do the GiF slot mod, which is ansolutely the best cooling mod out there!
See post 22 in this thread, plus in the thread various data on under bonnet temps.
https://www.jaguarforums.com/forum/x...-166641/page2/
In general, my personal opinion is that the symptoms of underperformance in the cooling system of your car that you describe indicate that you have a definite problem with the state of the OEM system that I suggest should be found and fixed before applying any other measures.

 

Adding my Aussie 2 cents.

The interior of these cross flow radiators needs to be professionally cleaned every 10 years or so.

The foam insulation above the transmission has a bad habit of dropping down and blocking EXIT air from the engine bay,. Pointless ramming it in if it cant get out.

All mine are sweet as, even in our 40+C summers and traffic snarls.

Read my stoicky at the top if you are interested. Comparing to modern cars systems is fraught with issues, and I simply dont go there. The system is fine, lack of care etc from 20+ years ago is the issue, and I stand by that.
Also, mine are all daily drivers, and 1 has just topped 800K kms, and never, ever had cooling issues. A pair of Aussie Ford Efans, in 1996, and the rest is as made in Coventry in 1976.

 

The V12 cooling system has a lot of places to go wrong, all well documented by now.... along with the fixes. And there's no question, IMO, that it must be kept at 100%. Faults must be identified and corrected.

Adequateness of the system depends a lot on what the owner expects and wants....and how much temp gauge paranoia he has acquired over the years

If the desire and expectation is that the coolant temp remain rock steady all the time, under all conditions, with any temp increase being intolerable, then the owner will find the system inadequate and might have a long and expensive....and possibly unsuccessful..... slog ahead.

If the owner can bear a modest (and harmless) increase in coolant temp in certain driving conditions then there's a good chance he'll find the system perfectly adequate.

Cheers
DD

 

Thanks for the input, I have looked through many cooling posts including the stickies. Cool to see many of the experts still very active on this forum. I have addressed some of the common issues and maintenance required of these systems, it is just hard to convince myself to pull the rad of a well running car especially during a colorado winter. As mentioned the viscous fan clutch was also replaced when I did this upgrade. There are a few things I still plan on addressing, including making a new front air dam. (maybe going crazy and addressing the bumper / full carbon fiber front body kit). As well as more comprehensive maintenance, I dont doubt the trans tunnel airflow may be impeded and the rad could use a thorough cleaning.

This project was primarily an upgrade to the electric cooling system and fan controller. After a few months of testing I am very pleased with its performance. It is vary satisfying to take the car out, get it toasty, and let the electric fans spin up then slowly come down in rpm as they successfully dissipate heat from the engine. Previously, the temp would just continue to creep up and I would stress and search for an open road to help relieve the cat. I also am found of its ability to push decent airflow after shutting down the vehicle to effectively combat heatsoak, as all modern cars do. After running the fans for about a minute a substantial amount of warm air is vacated from the engine bay and can be felt around the car. This is the difference between restarting the car abit below the N and well within the N range making me far more comfortable running errands in the car. I also now have the ability to set the electric fans to 100% to help this car stay cool through emissions.

The fans are accurately rated for 800cfm at a reasonable static pressure. Which most likely compares to 1000+ cfm of the embellished automobile fan ratings. There is a significant improvement of airflow through the electric fan and mechanical fan shroud with the server fans running. Additionally, the arduino will allow me to do some data logging of temps and other sensors which will be a fun project.