Well after what seems like months (because it was!) I finally have the thermo fans installed. I don't think I've done anything that hasn't been done before, and I have leaned heavily on this forum and its members (big thanks to Grant Francis). I still have some tidying to do, but the car worked fine in a driveway test, with one fan operating from A/C, the other from the water pump thermo switch. Here's what I did:

Ford AU Falcon twin fans and shroud from a wrecker, the shroud needed a little trimming down to make it thinner. That trimming down became more aggressive when my original plan for the radiator (re-core) became crazy expensive. So an aluminium radiator is in at less than a third of the cost, but it is a bit thicker (I've kept the original radiator in case I need it in future). There was a lot (a whole lot) of positioning, trimming, adjusting, repositioning etc to get everything in place, and it is tight! Thankfully the fans are clear of all moving parts by at least 10mm. They are very close to the terminals of the water pump temperature switch though, so I had to bend those terminals by 90 degrees to get some clearance. The mech fan bearing and tensioner are gone, replaced with spacers in the original bolts to keep the water pump in place. One v-belt in the bin!

I removed and replaced water rails, gaskets, crossover pipe etc, and that also took longer than I thought it would! New items include thermostats, the water rail tubing (in stainless), and crossover pipe (also in stainless). The bolts were a mongrel to remove, but only one needed some serious attention from a high grip socket - this was after treating all bolts to regular penetrating oil for a couple of weeks.

In doing the work I decided to pull my air pump off. It had been disconnected from before I owned the car, and therefore was pointless... except for keeping the large v-belt tensioned. What to do? Well, the alternator had its own belt, and I figured I could replace the air pump with the alternator, and then bin another v-belt. This was tricky. I had to do some filing to get the alternator to marry up to the water pump bracket, but it fit pretty well. Unfortunately raising it up meant that the main alternator lead was now too short (it will fit, but I was uncomfortable with its tautness), so I added an extension. I then got a bit stuck in how to tension the belt (the alternator had to shift downwards to do so). I was hoping to use a threaded rod from the air pump tensioner bracket to force the alternator down, but the "top" mount for the alternator was obstructed by the alternator body, so therefore I'd need some sort of bracket. Thankfully there was a straight line from that top mount down to the bracket where the alternator used to be tensioned from. Armed with a long threaded rod from the hardware shop, the alternator is now nice and tight. I got a very faint singing noise from the back of the alternator fan blades, as they are a little close to the belt itself. Out came the trusty file, and a quick bit of smoothing had that sorted out.

My AAV had been playing up before all this work. I don't like them. I know that these aren't a Jaguar only solution (I am pretty sure Mercedes used them on their cars in the 70s), but having had to replace one on an XJ81 I was keen not to do it again. Firstly, they are expensive. Secondly, they are a pain to get in and out, both due to access of the bolt heads, and due to the lack of give in the short rubber hose. Obviously with my water rails out, access becomes a lot easier, but I wanted a different solution. My car has non standard air-filters/airboxes, so doesn't have a means to lift idle once the A/C is on. In the past the idle has been set high enough to prevent the car stalling with A/C running, but after I fixed some vacuum leaks and readjusted my throttles, I decided that this is a compromise I can do without. I set the idle low (normal), but when pulling up at the lights with A/C on and clutch in, occasionally the revs would fall too fast for the car to catch, and it would stall. So I added an air solenoid where the AAV connected, and had a blanking plate made up in aluminium. The valve is from an early XJ40, and engages when the A/C is turned on (thereby raising the idle), and will also engage from a switch in the cabin (allowing me to warm up the car a bit quicker). Unfortunately this used part isn't great, and the solenoid sticks, so I will first try to clean it up, then either try to find a better one, or try some other air solenoid.

For the electrics, I mounted a relay box (6 relay slots, 6 fuse slots) near the expansion tank (where my headlight relay is). I pulled the horn relay into the box, and added an A/C relay, AAV relay, and a relay for each fan. The fans pull power from the bus at the firewall, each through 30A cabling and 30A circuit breakers (the blade-fuse style ones to fit in the fuse box). Triggers for the fan relays are the A/C clutch for one, and the water pump thermo switch for the other (this one switches to ground). The A/C clutch also triggers the A/C relay (no surprise there), but also the AAV relay through a diode. These relays (A/C and AAV) pull power through the brown cable that serves the horns through an old glass 25A fuse. Since this cable used to feed the original thermo fan and horns, it has plenty of potential to power the horns, the few amps for the A/C clutch, and the less than one amp for the AAV. Given the 25A glass fuse can be replaced with (roughly) a 15A blade fuse, I broke this up into a 3A blade fuse for the AAV, 5A for the A/C, and 7.5A for the horns. I'm not sure that I'd want all three running for minutes or hours at a time, but the horns are the thirstiest device in the circuit, and by their nature don't get used a whole lot, and certainly not for more than a few seconds a pop! The original fan diode pack has been removed, and the wiring terminated.

What's left? I need to bypass that 25A glass fuse - it's still in place with the four lighting fuses. I'll do that when I get a blade fusebox to replace the lighting fuses. The AAV switch to the cabin isn't installed yet, and I will be using the green towing warning light in the dash to illuminate when that switch is on - I'll do that when I get around to replacing the main fusebox with blade fuses! I need to tidy some wiring, and check that everything is tight.

The car and fans worked fine in the driveway, and it is now much quieter when revving. I had a small coolant leak from a blanking plug on a water rail, but everything else seemed to hold. The fans worked as I had hoped, the AAV substitute (as above), needed some rapping to work properly, and still sticks. The temperature-operated fan kicked in and out just fine. And the horns still work (bonus)! I have a pretty basic device that measures temperatures via thermocouples at each rear water rail (i.e. near the AAV on the left side and heater spout on the right). As the engine temperature rose, so did these, pausing when the stats opened, and stabilising as the thermo fan activated/de-activated. So far so good. I'll keep you posted when I get a good run in the car!

On an unrelated note, what was a small drop in my headlining at the back has turned into a problem - I guess there is always something to fix on these cars!

Thanks again to all for your help.

Dave

 

MAAAAATE, you need a BEER, or maybe a slab.

Awesome work, and very methodical, the ONLY waywith these beasts.

 

Great work, congratulations. Basically identical to what i did, including a solenoid extra air replacement, also all thanks to Grant's guidance.