Experience in a Book
Cooling System Upgrades

ELECTRIC FAN SUBSTITUTION FOR BELT-DRIVEN FAN: The best solution for fan clutch problems is to install a large electric fan (or two large electric fans) and remove the fan, clutch, mounting assembly (shaft & bearings), belt, and idler pulley altogether -- and perhaps the little stock electric fan as well. The Jag V12 is a hot beast, so the biggest electric fans that will fit should be used; a single 16", dual 14"s, etc. One benefit: we have all heard stories about how much power the belt-driven fan uses or even how much the belt itself uses, but the 16" electric fans typically draw about 10 amps -- meaning they use only about 1/8 horsepower when they are on. And if you control them properly, they're not on when not needed.

Electric fans can sometimes be mounted on the front of the radiator (if you can deal with the diagonal strut on the XJ-S), opening up considerable working room in the engine compartment. Many aftermarket fans are designed to be installed on either side of the radiator; to mount in front, typically the blade must be removed, turned around, and reinstalled, and the wiring must be reversed to run the motor in the "blow" direction rather than the "suck" direction. Note that a fan on the front side and blowing shouldn't have a shroud, but a fan on the back side and sucking most certainly will need one -- and the shroud that's integral with the fan is usually inadequate, what's really needed is a rectangular shroud to cover an entire end of the radiator.

There are lots of places to purchase 16" electric fans. Most local auto parts stores carry them, as well as J. C. Whitney. One of the best selections is from Jeg's. Peter Cohen offers another intriguing possibility: "Went shopping in the wrecking yard the other day for parts for the Volvo lump project. I came home with a 16" electric fan from an '83 Buick Regal ($20). This fan has a ring on the outer edge that is attached to the fan blades, and rotates with it. It is secured by three metal rods that go from the motor housing to two points on the lower radiator support brace, and one to the upper support brace. Interestingly, it also uses a ballast resistor, and 3 wires. One wire is ground, one goes through the ballast resistor, and one bypasses the ballast resistor, presumably to make a two speed fan." This author visited his local junkyard and found similar fans in a Delta 88 and a Toronado, except that they had plastic support structures instead of the metal tripod. Both had the same resistor arrangement for two speeds. The key is apparently to look for large FWD GM cars with a transverse-mounted V6; smaller FWD GM cars have a 14" electric fan, and RWD GM cars use belt-driven fans. Tip: take a 10mm socket and ratchet with you to the junkyard.

If you are shopping for a new fan, note that the Imperial brand 16" electric fans are reportedly unreliable; you'd be well advised to avoid that model.

One thing to look for in electric fans: a grille to keep your fingers out of it. Some have it, some don't (the GM OEM fans don't). If you're the kind of person that worries about such things, you might want the grille. The rest of us most definitely do not want the grille, since it reduces the airflow by a considerable amount.

Installation of electric fans requires more thought than simply slapping a fan in there. For example, consider the space between the A/C condenser and the radiator: with a blower fan in front, the air might come through the condenser, go sideways within this space, and come back out through a different part of the condenser -- providing excellent A/C but leaving the engine uncooled. Similarly, a sucking fan can pull air from the engine compartment through the radiator backwards, across the space, and back through the radiator to the fan -- leaving the A/C condensor without airflow, and eventually overheating the engine from recirculating the same air. If the space between the condensor and radiator is open to outside, things get even worse. In the XJ-S, one tempting possibility is to mount one 16" electric fan in the existing shroud on the right side of the radiator (replacing the stock belt-driven fan), and a second 16" fan on the left front of the radiator blowing through the A/C condenser; this would make sure that both coils get airflow. Another possibility is to just replace the belt-driven fan with an electric and leave the small electric fan and the entire shroud assembly as stock.

John Napoli went this latter route, and reports on the process: "Removing all the stock stuff is a bit of a pain -- there is not much room to work, the process is iterative -- but it all comes out. You'll have to replace a couple of the water pump bolts that went through the idler pulley bracket with shorter bolts. Remove the radiator while you are at it to clean out the leaves in between the rad and the condensor -- I seem to recall that if you pull the rad first it is easier to get out the stock fan.

"I kept the stock electric fan and added the second inside the shroud of the old mechanical fan. The fan shroud is split from the factory (little fan and big fan) so this is real easy. I used an ëS' bladed fan from a Hot Rod supplier - 1-800-strt-rod or somesuch - it is the largest one they had (17" or 18"). Any fan of similar size should be fine; you can get them from Pep Boys or JCWhitney. Be sure to run the fan before installing it. Some are out of balance. Mine was, and you would not believe how annoying it is! I had to balance the blade (wrapped solder around the light spots and used weatherstrip adhesive to lock it in place) but it would have been better to start with a perfect unit.

"I made brackets to hang it off of the stock shroud. It fits in there nicely and the underhood appearance and access is improved. Do not under any circumstances attach the fan to the radiator core with those silly little plastic thingies! The Jag radiator is softly mounted to absorb vibration. Use those shortcuts, and the new fan will quickly work loose.

"Performance has been fine as measured on accurate mechanical water temperature gauges. I like overkill, though, and may some day add one or two little pushers in front of the condensor." Note: a better way to evaluate fan adequacy would be to measure the temperature of the air coming through. A marginal capacity fan may keep the coolant within limits but the air coming through the radiator will be really hot, while an excessive amount of airflow will minimize how much the air heats up. Of course, comparisons would have to be done on similar days with the engine running under similar conditions.

Tip: If you are removing the stock mechanical fan bearing support, you will need two studs 4-1/4" long with 5/16"-18 (coarse) threads on one end to continue to hold the water pump properly. The other end of each stud can be either coarse or fine thread, since it gets a nut and you can use whatever nut matches. Good luck finding such studs! Alternatively, you can use threaded rod cut to length, or you can cut the original stud shorter and thread it. Or, you can just stack washers on the existing stud if you don't need clearance in the area for the motor on your electric fan. You will also need two 5/16"-18 bolts 1" long, but those are easy to find.

CONTROLLING ELECTRIC FANS: Electric fans can be controlled by either of several mechanisms. The simplest method is to wire the fans to run whenever the ignition is on. This is wasteful, however, since the fans are only needed when the car is standing still or moving slowly. It also may cause the engine to run cold, or take too long to warm up, in cold weather.

The electric fans could also be connected to the existing electric fan control system, which automatically operates when the engine is hot or when the air conditioner is operating. Note that replacing the single tiny fan with a couple huge ones requires more electrical work than simply installing a larger fuse in the #1 position in the headlight fusebox; the stock wiring, even if it doesn't burn up, will provide too much resistance and the fans won't run as fast as they should. Some suitably heavy wiring should be run from the buss on the firewall to the new fans, using a separate relay for each fan. Napoli: "I wired the new fan simply: I added a relay that is picked up by the stock (ie, little) fan coming on. The power for the new fan is routed through the relay from one of the 12 volt feeder wires located near the relays at the upper rear corner of the right fender. You can get fancy and route alternative feeds from the A/C compressor or a dashboard switch, but if you do you may need a diode to prevent backfeeding something else."

Yet another possibility is to add another fan switch into the coolant system. Jaguar makes a suitable housing for a switch for the Mk III E-type, C34005, that fits into a radiator hose, or maybe you could get lucky and find a switch that will fit one of the unused ports in the water rails on top of the heads. Or, there are switches sold for electric fans that just strap to the outside of a pipe, so you could just attach it to one of the coolant pipes -- or oil pipes, for that matter. With any such switch, one of two fans can be connected to the stock wiring and the other to a separate switch. This would result in the two fans operating separately, and only one running when only a small amount of airflow is needed (since one fan will always come on before the other). The dual circuit also provides a measure of redundancy, since one of the fans would provide some cooling in the event of the failure of the other circuit.

The fans could also be controlled via an air temperature sensor in the air coming through the radiator. This method is often used by the aftermarket fans, providing a switch that mounts right on the fan housing. Note that if the fans are mounted in front of the radiator, the sensor must be moved to behind the radiator to work properly. This method scares me, since I always wonder what would happen if there is no air coming through the radiator -- like, the car is stuck in traffic and there's a slight breeze from behind.

Yet another control system would be to provide a "paddle" switch that shuts the fans off when the airflow due to car motion is adequate. There don't appear to be any such items commercially available, but making one would not be difficult. A pivot with a paddle on one side and a tiny counterweight on the other, balanced to eliminate inertia effects, could be installed in the area behind the front grille. The arrangement could be rigged to operate a conventional microswitch with contact ratings sufficient to operate the fans directly, or a relay could be incorporated. Using an ohmmeter or a light bulb, the car can be tested and the switch adjusted until it operates at a suitable speed, about 30-40 mph. This system would still operate the fans when the engine was cold, but would function properly with the air conditioner; the air conditioner requires airflow when running even when the engine is cold, but the motion of the car above 30 mph will be adequate; turning the fans off is OK.

Finally, remember that you can use a combination of the above schemes; for example, you could use a paddle switch along with a temperature sensor to prevent the fan from operating when moving fast or when the engine is cold.

If the control scheme used allows any possibility that the fans will be off when the car is idling, be sure to incorporate circuitry to run at least one fan whenever the air conditioner is operating (similar to the present wiring for the small stock electric fan). On some later XJ-S's, the small stock electric fan does not come on with the A/C, but remember that this is assuming a belt-driven fan that is always turning; regardless of the stock wiring, if the belt-driven fan is removed you must provide fan operation when the A/C compressor is engaged, regardless of engine temperature or outdoor temperature.

One final note: another nice feature of electric fans is their ability to run after the engine is shut off. The biggest heat problem in the XJ-S is heat soak after shutdown. The small electric fan already can provide some relief if the coolant is hot enough for it to be on when the car is shut down, but having multiple electric fans and multiple control schemes provides more possibilities for addressing this issue. It might even make sense to provide an air temperature sensor at the upper rear of the engine compartment to control post-shutdown fan operation. Or, maybe using a hot-start sensor in the fuel rail to control a fan would help with hot starts more than the way it's normally used (to alter fuelling).

RADIATOR HOSE FILTERS: Almost everybody who has taken their XJ-S radiator to a shop and had it rodded out has been told that it was really plugged up. The Jaguar recommendation to use Barr's Leaks in this system is often blamed, but there are apparently other contributors as well. Rust scale coming off the inside of the header tank and crossover pipe is a source of crud. Some mechanics use too much silicone sealant so it leaves a bead around the joint, and later on this bead peels off and starts looking for a passage to plug. And those who replace their coolant often but mix it with hard tap water are introducing a whole new supply of minerals with each change; when the engine heats up, all these minerals deposit on hot engine parts as a scale, and then peel off in chunks and go looking for passages to plug.

Why don't they make a "last chance" filter to install in the upper radiator hose to catch all this junk before it can get into the radiator and plug things up? There are no small passages in the engine, the chunks could just flow right through the block, but catching them before the radiator should greatly extend the time between roddings.

They do. Brian Schultetus provided the source:

Gano Filter Company
1205 Sandalwood Lane
Los Altos, California 94024
+1 (650) 968-7017

This company makes a filter that is essentially a conical screen in a tube. The basic model is a clear plastic tube so you can see the filter getting crudded up and know when to replace it, but some people don't like plastic so they offer a brass tube model as well. They also claim that the screen is made of the same copper alloy as the radiator itself, so it also serves as a monitor for corrosion. And they point out that merely having the clear tube can provide considerable information on what is going on in the cooling system.

The filter comes in three sizes, and of course they expect most customers to buy one per car. The V12 has two upper radiator hoses, though, so you will need two filters. The hoses are 1-1/4" in diameter, which corresponds to Gano's "small" size filter.

HEATER HOSE FILTER: Gano (see above) also offers a small filter assembly for installation in the line to the heater core, pointing out that the same crud that plugs radiators can also plug heater cores. Your immediate reaction might be "Who cares? If the heater core gets plugged, it doesn't damage the engine." However, you might want to rethink that reaction. The heater core getting plugged might not damage the engine, but it'd still be no picnic to fix.

Unfortunately, the Gano heater hose filter assembly is only available in brass -- no clear plastic version offered -- and therefore must be disassembled to check for pluggage.

On the plus side, you don't need to get this item from Gano; it's available in any hardware store! All it requires is a pair of fittings for a 5/8" garden hose, and one of those hose washers with the built-in conical screen intended for supply hoses for washing machines and dishwashers.

Garden hose fittings generally come in three flavors: The plastic junk, the slightly better "corrogated" brass (made of thin brass formed to shape), and actual high-quality fittings machined from solid brass. Besides being considerably more durable, the solid machined brass items also typically have flats around both male and female fittings, making it much easier to tighten and loosen. This being the US, most consumers are morons who buy the plastic junk, and most retailers are also morons who cater to this stupidity rather than making the slightest efforts towards educating their customers on why a better product is the wiser buy. So, the solid machined brass items can be a little hard to find.

Home Depot carries an excellent set. Made by Nelson, item N-1558 B, "5/8" Brass Hose Repair -- Extra Heavy Duty Rod Brass" contains a male fitting, a female fitting, two SS worm screw hose clamps, and one rubber washer -- in other words, everything you need except that you'll need to pitch the simple washer and install a screened washer instead. This set costs about $5, and the screened washers are perhaps 3 for $1. With a little shopping you can actually find screened washers in two or three different screen grid sizes; the ones with the biggest holes are suggested -- the fine ones are really fine. After screwing the two fittings together with this screened washer in the middle, just cut the heater hose between the engine and the heater valve and install this assembly with the clamps.

Cleaning this thing should be easy, since you can easily install this thing at the very highest point in the system and not even have to do any draining. Just unscrew the two hose fittings from each other, clean out o better "corrogated" brass (made of thin brass formed to shape), and in the line reduce flow to the heater core? Perhaps. Here in FL, we couldn't care less; any flow at all is enough, and most of the time we'd rather have less flow. But you guys who live in the less habitable climates might think before installing this screen. I have this suggestion: Install the screen assembly, and then when winter approaches unscrew the fittings and replace the screened washer with a normal hose washer. That way, you get filtration in the summer, full flow in the winter. With any luck at all, the filtration in the summer will take enough of the crud out of the system that there won't be any pluggage during the winter.

Such a screen installed in the heater line might actually save your radiator! Since this essentially becomes a "bypass filter" arrangement, eventually this tiny screen should remove most of the crud circulating around the closed coolant circuit. The only problem will be the crud that jams tubes in the radiator before ever going through the heater hose, but if you're really concerned you should be buying the Gano radiator hose filters above. The other shortcoming is that, since this screen is so small, it's likely you'll have to clean it out a lot of times right after installing it until you get the system pretty well cleared up.

Post-Shutdown Cooling

It it commonly acknowledged that the worst cooling problem the XJ-S has is not when running, but after shutdown. The small electric fan runs after shutdown if the thermal switch has it running when the engine is shut off, but once the switch cuts out -- which it does all too soon, since it is reading coolant temperature at radiator outlet -- it will not come on again. 700 pounds of hot engine plus hot exhaust manifolds and hot catalytic convertors tend to raise the underhood temperatures after shutdown considerably higher than they ever were while running, and there are indications that parts of the engine itself get hotter after shutdown as well.

There are three problems generally associated with post-shutdown heating: Dropped valve seats, hot start difficulties, and heat-stressed engine compartment components. The exact mechanism of dropped valve seats is unclear, but several owners have suffered dropped seats after a hot shutdown rather than while running. The other two problems are clearer, and result from the high temperature of the air surrounding the engine -- and all the extraneous components that are heated by the air. Since there is no longer fuel flow in the rail, the fuel sitting in it gets hotter and hotter, causing serious hot start problems that Jaguar has addressed with a coupla different types of fuel rail temp sensor providing fuel enrichment. The post-shutdown underhood temperatures are clearly a key cause of deteriorated hoses, brittle wiring, short-lived electrical components, and a host of other traditional Jaguar afflictions.

This section includes several ideas for dealing with the post-shutdown temperatures. Most address primarily the temperature of the air within the engine compartment, which may or may not have a significant effect on the temperature of the heads themselves in the vicinity of the valve seats.

HOOD VENTS: Just the ticket for letting the heat rise naturally out of the hood after shutdown. It's a body modification, so it's discussed further in Body Modifications.

ELECTRIC COOLING FAN BOOTSTRAP CIRCUIT: The electric fan includes a "bootstrap" circuit, so that if the coolant is hot enough for the fan to be running when the engine is shut off, the fan will continue to run until the coolant temperature switch shuts it off. Once off, the bootstrap circuit drops out and the fan cannot start again, no matter what.

Other cars -- notably Japanese and other FWD 4-bangers -- have cooling fans that cycle on and off for quite a while after the engine is shut off. Clearly, they are wired so that the fan will run if the thermostat calls for it, regardless of whether the ignition is on or not. It is also evident that they come on -- indicating that once they shut off the first time, they may still be needed again. Probably the engine heat soaking through the compartment.

Why did Jaguar provide this bootstrap circuit, rather than just wiring the fan to run when needed like the Jap cars? There would be two possible results if the bootstrap weren't in there: 1) The fan would never come on after shutting off the first time -- meaning that the bootstrap circuit was unnecessary; or 2) the fan would come on after shutting down, which means it needs to come on and the bootstrap circuit is contributing to the cooking of the engine parts!

The only plausible explanations: A) Jaguar was afraid the Lucas thermostat would fail in the on position and kill the battery; B) they didn't feel that a fan kicking on and off in the parking lot was in keeping with the proper Jaguar image; or C) they were worried about liability from someone having their fingers in there when a fan came on unexpectedly. Stuart Barnes adds D) "Many car alarms are voltage sensing and although they can cope with a voltage rise (to allow an electric fan to run and then stop) a lot of the aftermarket varieties can't cope with the voltage drop that would occur when the fan came back on."

For those of us who are more concerned with the life of our machines, keep our fingers out of moving machinery as a force of habit, and don't have such alarm system concerns, it might be a good idea to rewire that circuit to run the fan whenever necessary. It's easy to do: On the left side of the engine compartment is a small blue box that looks like a relay, but it's the diode pack. Pull the LG wire off of terminal 4 and connect it to a 12V power supply. There is a 12V supply available at the solid brown wires at the headlight fusebox just a few inches forward of the diode pack.

Note that, if you have headlight washers and wipers, the blue box might not be the fan diode pack.

ENGINE COMPARTMENT AIR TEMP SENSOR: Another way to get the electric cooling fan to run longer after shutdown might involve adding an air temperature thermostat within the engine compartment -- preferably high and rearward, where the post-shutdown cooking problems are the worst. This thermostat could be set at a much lower temperature than the one in the coolant and still wouldn't come into play while the car is moving or the engine-driven fan is circulating air. But if the air starts getting hotter after shutdown, it can come on -- even if the coolant in the water pump isn't that hot -- and flow some cool air through the engine compartment.

Imperial makes a dandy little "Adjustable Thermostat for Electric Cooling Fans", number 226203, available at Discount Auto Parts. It's really an air temp thermostat. It has a remote bulb sensor and includes instructions for mounting right on the back side of the radiator core, but you could mount it anywhere -- even on the underside of the hood! The thermostat is adjustable from 248†F to 32†F, and the contacts are heavy enough to control fans directly without relays.

ELECTRIC COOLING FAN POST-SHUTDOWN TIMER: Michael Aiken's plan: forget relying on temp sensors and simply provide a timer that runs the fan for a fixed amount of time after shutdown. Aiken used one of the existing 10-minute seat heater timers to provide this fan operation, and provided the wiring scheme shown in Figure 26 which automatically starts the fan running on the timer whenever the engine is fully warmed up and shut off. Aiken points out that this is not an unheard-of idea; the Nissan 300ZX uses a similar scheme with a 17-minute timer. 

Aiken describes this scheme: "The timer is activated by grounding pin 1 and then releasing it. It will not activate if pin 1 is held to ground. I left the manual switch (on the side of the console) wired in so the light would show when the fan is on, but that is optional." Having the pushbutton may have an additional benefit: you can push the button to force 10 minutes of fan operation whenever you wish. This might be handy if, for example, you get stuck in downtown traffic; you can simply tell the fan to run continuously for 10 minutes rather than cycle on and off with the thermostatic switch operation.

"The capacitor is a 2000µfd electrolyte and the diode is 3 amp. The capacitor attaches to ignition key 12V output in position 2 and 3. This is important to keep the fan from coming on during startup (position 3)." Ed. note: the wires that meet this criteria are white, as has been indicated on the schematic. They are connected to terminal 3 on the ignition switch.

"When 12V is applied to the capacitor it charges through the diode. When the ignition is turned off the capacitor discharges back through the relay momentarily (about .5 seconds) activating it and starting the timer relay. The fan runs for 10 minutes and then shuts off. The thermostat in the ground leg prevents the capacitor discharge if the engine is not yet warmed up. The capacitor does hold the charge and will discharge later if the temp reaches the set temp -- even several minutes after shutdown. I set my temp at 180†F."

The schematic shows the output of the timer (pin 4) connected through a diode to the wire from terminal 1 on the diode pack to the fan relay, so it will directly close the relay and operate the fan. Radio Shack catalog number 276-1661 will serve nicely for this diode as well as the other one used in this scheme. In this application on the timer output, the diode only serves to make the indicator light show that the timer is engaged. If this diode is omitted, the system will still work just dandy but the light will be on whenever the fan is running, even if it is the A/C compressor control or the stock coolant switch operating it.

If you happen to have one of the later cars where the A/C compressor does not bring on the electric fan (as Aiken has), you don't have to buy a new diode for this task; there's an unused one in the diode pack. Just connect pin 4 of the timer directly to terminal 3 of the diode pack.

Aiken also points out that this scheme doesn't have to control the small stock electric fan; it could be used just as well to control an aftermarket electric fan, or anything else electrical you'd like to run for 10 minutes after shutdown. The use of a marine bilge vent fan has even been suggested. It's probably not a good idea to operate a large fan or multiple fans; it shouldn't take much airflow to keep the underhood temperatures within reason, and you don't want to strain the battery. The fact is, the stock Jag small fan is probably perfect for this job.

Since Aiken used the seat heater controls, the schematic shows the timer and the pushbutton with indicator light as they appear in the Jaguar seat heater schematics. Of course, if you'd rather leave your seat heaters wired as originally intended -- or if you have an earlier car that doesn't even have seat heaters -- you can simply buy a new timer from Jaguar, or perhaps a generic timer (or maybe the one from a Nissan!). You can simply leave the pushbutton and indicator light (and the related diode) out of the circuitry altogether if you wish and connect terminal 30 of the relay directly to pin 1 on the timer. Or, you can buy any generic momentary pushbutton switch; don't let the excessively complicated Jaguar illustration fool you, that heater switch is just a normal momentary single contact switch with a built-in indicator light. If it's only the indicator light you want, you can skip the switch altogether and simply buy any generic 12V indicator and connect it to pin 4 on the timer and to ground and mount it anywhere convenient -- or you could wire it to one of the unneeded warning lights in the dash.

Aiken apparently left his timer where it was originally mounted behind the dash, but if you're installing a new timer you can pretty well choose anywhere to install it. Other than 12V power -- any brown wire -- the only thing you really need is access to a suitable white ignition wire, and they are all over the car -- even going to the EFI power relay in the trunk. There is also one to the ignition system on the engine, so it's possible to install all of this stuff someplace near the fan itself -- perhaps in front of the radiator, or in the compartment behind a headlight -- and not have to run any wires into the passenger compartment, provided you don't want a pushbutton or indicator light.

On to Drivetrain Modifications