We're in a bit of a heat wave for San Francisco. I drove in heavy traffic yesterday and noted the temp gauge was higher than usual. It was just beyond the 0 of the 90, so just a bit to the right of vertical. That's unusual for me. I parked in the garage and went down 30 minutes later and it looked like my jag had peed a bit. It was hard to figure out were it came from but I had coolant in the bottom of the reservoir. I thought i had a leak, but in reading about this, I had previously filled the reservoir thinking it was supposed to be that way. So I think it just was vented as an overflow situation. Today I took the car on another trip in heat. There was stop and go traffic on the GG bridge and up the hill on the Marin side in pretty toasty weather for us. Same deal on the gauge - just beyond the zero of the "90" on the temp gauge. It went back down to mid line as I went down the hill to Sausalito.

So I have some questions:
Does the temp going beyond the zero indicate I might have problem.
How does one check the general functioning of the coolant system? Is there a way to tell if your thermostat or pump is not functioning correctly?
If you overfill the system, from where does it empty when it vents? I can't really see where the fluid can from. I checked all hoses and don't see any leaks.

 

maybe from the "bladder" tank located under the left fender. It's a recovery tank for the recovery tank.

Is the auxiliary fan not coming on? It usually keeps the temp in check.

 

Maybe from the "bladder" located under the left fender. It's a recovery for the recovery.
Thats the right location. It was coming from the left fender area. Didn;t know it had a bladder -- maybe I can just use a catheter.

Is the auxiliary fan not coming on?
I don't know, I can see if its seized. But Ill have to get the car hot again to see if it comes on. Its supposed to come on either 90 or 95 I believe

Thanks - good idea

 

Do you have the metal reservoir or the brown plastic one? Just curious. Either way, filling it right to the top isn't needed or desirable.

As discussed, it is possible the system was overfilled and simply ejecting the excess.

The tank hidden in the fender should be about half full when cold. If it is overfilled it cannot accept the overflow from the first tank...the one in the engine bay.

The theory is that hot coolant expands into the hidden tank and is drawn back into the first tank when it cools. If it doesn't get drawn back in the hidden tank becomes over-filled. The pressure cap on the first tank has a valve to allow the coolant to be drawn back in. It might be faulty

So, when cold check the level in the first tank. If it is about 1/2 full or so leave it as is and drive the car. If no more drips, and the coolant level in the first tank is OK when rechecked cold, there's probably nothing more to do. If continued drips and/or the first tank needs filling again, you probably have a bad pressure cap




Under the conditions you describe there's no problem with the temp gauge rising a bit.

If it keeps going up-up-up, you have a problem. If it rises a bit in mild ambient temps, you have a problem

The cooling fan should be coming on at about 94ºC. From what you've described I'd say you're right on the cusp of that.

Cheers
DD

 

I doubt the aux. fan is seized, those fans are tough.

It's either the thermal sensor at the bottom right of radiator, or the Red relay mounted to the radiator support, or the fuse in the aux. fuse box next to the first coolant tank.
(one fuse is for the aux. fan, the other 4 are one fuse for each headlight).

 

Did the trouble shooting. I don't think the ax fan is coming on at all . But it I can get iit to run if I bypass the thermal sensor. So I ordered one and will see if that does the trick. Thanks for your help

 

you will lose coolant when replacing that thermal sensor, and will need to bleed the cooling system of air. It's a messy job.

 

Yeah - I dont even see how I remove the damn thing. I'll see if I can find a stubbie wrench with a shaft that bends.

I was wondering if it would be easier to set the fan to go on when the ac clutch is engaged. I'm not sure where the AC clutch relay is. But it seems that would be a pretty easy fix for the time being. Thoughts?

 

you need a large wrench to turn that sensor. It will be tight, and it's a big hole in the radiator, coolant will come out with force.

yes you can mod the fan to run with compressor, but it is a noisy mod, sounds like a Maserati.
There is no clutch relay, the mod consists of adding a diode inline, jumped to one of the wires from the fan's Red relay to the
com​pressor plug.

 

Did you bring the wrench from above or below. And did you remove anything to get access? I tried a to see how I would do it and just cant seem to find a angle yet/. Waiting for the sender unit so I cant do until then. Is there a process for bleeding air out of the system.

 

remove the air filter trumpet and canister, remove the under-car splash panel. Place container under sensor to collect coolant. Disconnect thermal sensor.

Not easy to remove, you will have to get leverage from above and from below.
The longer the wrench, the easier it will be, unless radiator is completely removed from car. A massive job.

 

Massive is the word. I think the hot wire might be the way to go. Not not an electrical wiz. What I was think was putting a resistor to decrease the fan speed a bit so it not so loud. I found a thread where someone stuck a resistor because they wanted half speed with the ac. I'm not sure I under why the diode is needed? Jose, If you know which diode would work and how exactly to the do this -- I would appreciate a descriptio assuming I love this stuff, but do not have any experience creating new car circuits. This actually sounds like fun to me. Thanks

 

it was a popular mod for the XJ-6, the XJ-12 came already wired like that from the factory.

Back in the 1990's, there was a guy who sold a kit for $10. to do the mod. A lot simpler to do than replacing that thermal sensor.

my '84 is modded like that, but the noise ! Also you don't want the fan running in winter temps, so it must be disconnected.

I think there are instructions somewhere, maybe Doug knows where, if not I will try to find my instruction sheet.

 

I saw this water temp joint pipe sensor. If the thermo sensor has a 10mm thread -- which is probably doesn't - one could splice this in one of the coolant hoses. The comes in a variety of sizes so I bet one can find a hose that is the correct size. At least it would be easier to change in the future. I realize you still have the messy coolant issue -- but you wouldn't need to change the wiring and you wouldn't lose the back of your hands trying to remove the sensor where it is. This would all depend on whether the threading of the thermosensor would work. It's been 5 years since my coolant was flushed -- so I could rationalize the mess to some degree.

https://www.aliexpress.us/item/32568...2usa4itemAdapt

 

It is your car and you do it as you prefer, but I would keep it original.

Forget the thermal sensor for now and do the fan mod, just to see if the fan running keeps the temp down in the heat wave.

The compressor is ALWAYS ON in these cars, Regardless of settings, so the auxiliary fan will always be ON too with the fan mod.

I am looking for the instructions.

 

Vague memory disclosure here but I recall the fan mod being more for improving A/C performance under conditions where there was little airflow thru the condenser---city driving, long stoplights, etc.

To find out if the aux fan will or won't make a difference in the temp reading just jump the sensor wires together so the fan runs and go for a drive.

If the aux fan runs all the time, due to the compressor always running, I'd be a little concerned about the expected life of the 30-40 year fan motor. Just me.

Personally I'd just dig in and replace the temp sensor and forget any mods. That's just me

Cheers
DD

 

not to mention an additional electrical load on the alternator with aux. fan running continuously.
Ideally, I would add a Dash Switch to turn ON and OFF the auxiliary fan when temp goes above the center mark.

 

Yeah -- I suppose fixing the car to spec is usually the right answer. Still unsure how to grab the sensor without removing the radiator - but mother nature has intervened and the heat wave is over in SF. Had the heat on this AM. If anyone has info on a tool or strategy they used to do this -- please let me know. And Jose -- hope you're not the the crosshairs of the storm. Stay safe.

 

I'll only consider this if I can't change the sensor -- but I think I found the axillary fan mod mentioned above. My solution for accessing the sensor: use a torch to bend a wrench at an angle that will reach it. According to the information I found, you can use either a 29mm or 1-1/8 wrench for the deed.

"Mike and the List,

Hi List, Here is a procedure for adding the diode so the aux fan comes on
with the compressor. This mod will cost less than $10.00. It will lower
high side pressures on cars with R-134a by 30-50 lbs when the car is not
moving, greatly enhancing cooling when stuck in traffic, and keeping the
system from blowing the hoses and seals out. It is even beneficial to R-12
and R-406 cars. The parts and supplies need are readily available at any
Radio Shack or any electronics parts house.

Tools Needed: Soldering iron, crimping tool, wire strippers, pliers
Supplies needed: Solder (rosin core), 2 feet of insulated wire (recommend 18
gauge), diode (1N4001, 1N4002, 1N4003) or equivalent, heat shrink tubing
(assorted sizes and lengths), some type of disconnect crimp-on connectors,
male and female (spade type will do, bullet type better, aviation knife type
best but hard to find, a couple of 3-way splicing connectors if you don't
want to cut any wires).

Procedure:
1: Disconnect the negative battery cable. You will be working with/near
wires that may have power applied even with the ignition off
2: First of all, locate the wires you will be splicing in to. On the A/C
compressor side, it is the 12 volt wire going directly to the compressor
clutch. On my car this is a green wire going directly to the clutch plug.
This is one of the two you will be tapping into. Do NOT use the black wire as
this is ground (earth). Next, remove the plug going to the aux fan relay
(normally a red Lucas relay or maybe a black Bosch one like mine). It's on
the left side near the top of the radiator support frame on the engine
compartment side. Next locate the Green wire with a white stripe going to
this relay. It is the one farthest to the right when plugged in and mounted
normally. This is the other wire you will be tapping into.

2: Next, make up the diode harness. Cut the length of spare wire in half,
strip one end of each wire and solder one piece to each of the two leads
coming out of the diode. (If you don't have soldering skills or equipment
you can use red butt type crimp connectors here, just make sure they are
tight). Identify the "cathode" end of the diode. It is the end with the
marker band around it. Tie a knot or otherwise mark the wire attached to the
cathode end as not to get them confused later. Then take a piece of heat
shrink tubing just big enough around to slip over the diode and long enough
to cover all bare wire and heat it to form insulation around the diode.
Repeat this process as to end up with two layers covering the diode and
exposed wires.

3: Connect It. Using the three way splicing connectors or other means that
you like, connect the end you marked or tied the knot in (cathode) to the
green/white wire you located previously which goes to the connector to the
fan relay. I like to use disconnect type connectors somewhere in line here so
this can be disconnected for any troubleshooting that might be needed in the
future. Next, connect the other end of the wire attached to the non-banded
(anode) end of the diode to the green wire previously found going to the
compressor clutch plug, making sure the wire is routed so that it will
interfere with nothing else.

4: Test It: Reconnect the negative battery cable. Turn the Climate control
off. Start the car. Verify the Aux fan is not running. Turn on the A/C.
Verify the aux fan is running. Turn A/C off with car running. Verify the
Aux fan is not running.

Notes:
1. No additional fusing is needed as this mod simply uses the compressor
clutch power to activate the relay that powers the aux fan.
2. Some Jaguar schematics show a diode in exactly this position for this
function, although some show it opposite polarity than is needed, (a misprint
I'm sure). Some later prints show it correctly.
3. Apparently, some cars come like this from the factory, mainly 12 cyl
versions.
4. This is a first draft of this procedure and I've made every effort for it
to be complete and correct. I certainly welcome any corrections,
clarifications, or better ideas.

Steve Randall
85XJ6 with COOL A/C"

 

dk65,

The other albeit temporary assist to get a bit of extra cooling - particularly if it's rarely and nominal needed - is simply to "pop the hood" and let the 1' or so of full venting allow a lot of the hot air that has built up to escape.