So I noticed that My temps go past the "N" on the gauge and will go get close to the H but when the top fan comes on the needle returns to just right of the "N". Especially during hill climbs and traffic. So I checked thw fans and noticed only the top right fan comes on. The lower left never does, so I unhooked power to the top right and hooked it to the lower left. It runs at the same temp that the top right does when connected. So I know the lower left does run when supplied with power. But Im new to this car at what point should the lower left run? Are there any modifications that I should consider before chasing down the problem. No harnesses are burnt or melted and the Green relay was super clean when I disconnected and reconnected it. TIA!

 

Sounds like you may not have a thermostat in the housing!

Wouldn't hurt to pick up a new thermostat and swap it out even if you DO have one in there ..On a '94, gauge should never really go past "N" even on super hot drives/days. I did a 15 mile steady climb in summer and the gauge never budged.

I'm not sure about the fans working independently, I never had an issue with them (other than staying on for too long after shutdown ) - I always assumed they work in tandem, they get the power from the relay which in turn gets it's go-ahead from the sensor in the rad.

If it were my car, I'd check continuity to the lower fan first and if ok, probably suspect the green relay ...but if the fans ARE designed to switch on independently I guess the relay could be ok - check the circuit diagram to see if the relay has double switches inside, if not, I'd try a replacement.

Larry

 

Thanks Lawrence! I ordered a new Tstat today. Will get to replacing it stat! Im not the greatest at reading electrical diagrams but nows a good time to start.Did manage to find this online.

 

All XJ40, X300, X308 fans run the same way.
All are interchangeable.
The low speed is SERIES and the high speed is PARALLEL.
Check the fuses. (30 amp for each fan)

bob

 

Just for clarity, I know the above statement is true of the late XJ40s ('93-'94), because I put X308 fans in our '93. I just had to change the electrical connectors. But was the same fan used in the '90-'92 cars with one electric fan? I recall that the early XJ40s had a fan with a belt-driven thermostatically-controlled viscous-coupled clutch.

Cheers,

Don

 

The 1988-1992 had the mechanical fan. The supplemental electric was completely different.

bob

 

So I checked the fuses and theyre good. The fuse box on the drivers side footwell. I belive the first one was listed as cooling fan A and A+B, the second fuse was listed as cooling fan B. Could be the relay. I do have a multimeter. How do you check for continuity in the non working fan with the harness connected to the fan? As for voltage,I imagine that I can insert the leads of my multimeter into the power harness for the lower fan to see if Im getting voltage when the upper one kicks on. Lemme know if Im going about it the right way please. 🙏

 

Check out this post by Larry, in which he quotes a post by Bryan N at the Jag-Lovers forum in which he explains the fan operation:

https://www.jaguarforums.com/forum/x...7/#post1509517


Cheers,

Don

 

Now if I could only remember all that stuff!

Larry

 

Wasn't someone just wrestling with fans not working? Ill go check and be right back.
Looking down the list, I think the thread I was Actually thinking of was Makulas' stalling problem..... Still, might be worth it to search down the forum .... Good luck

 

I took a look at a few other threads and wow! The wiring of the fans in unbelievable! My AC is a bit low on coolant because it wouldn't work a few days ago, but I decided to add some r134 and I actually get some mildly cold air now, but I could still be low. The gauge on the canister I was using started to read that I was full on Refrigerant so I decided not to add anymore. A proper set of gauges is the way to go here. I'm going to replace the Tstat tonight, so hopefully that will help keep my temps down. The Previous Owner stated he had it replaced a year ago. I called the shop that worked on it and they confirmed it, but Im just not 100% convinced they're a very good shop, even though they're a Jaguar shop. They could have used an aftermarket Tstat and thats a problem

 

When I replace the Tstat, do I have to use any kind of sealant along with the paper gasket that came with the new Tstat? Or do I just apply the new gasket dry between the engine and housing?

 

I personally use Permatex Ultra Grey RTV sealant and no paper gasket and I've never had a leak. If your old thermostat uses an O-ring seal, I would recommend that you use a new O-ring and supplement it with some Ultra Grey on the cover rim. Here's a link to photos of the job on our '93:

Coolant Thermostat Replacement

Cheers,

Don

 

I did receive a new rubber O ring too. Thanks Don!

 

Okay replaced the Tstat and going to test drive tonight. Do I need to burp the system somehow?

 

I don't recall ever having to burp the cooling system on an XJ40 - I'll be curious to hear if others have.

Cheers,

Don

 

Thanks Don! I drove the car to pick up food and the needle was Solid at "N" didnt move like what Inwas used to seeing. I will have to drive it to work tomorrow and give it a little push to confirm that allnis fine. But I can tell already that things are better, I even have more heat coming out of my vents. Larry thanks for your input in this too. The hot days are rolling in and Im sure my cat will be happier running at lower temps again. As for the lower fan, Im thinking about modifying it so that Im able to run it via a switch. As long as the top right fan is working correctly, Im sure I will be able to run the car with a manual switch. I think the key is to find a switch that is automatically On when powered so that if not needed I have to manually shut it off.

 

The problem you might encounter is that the fans were designed to run in series on LOW and then progress to HIGH when commanded. A single fan will only JUMP to high and the fuse might 'blow' from the high current demand.

Read some TSBs for info.

Some of the TSBs are for the X300 but they share the same operating principle.

bob

 

Thanks for the tech sheets! Its really hot out today and the car has been behaving just like it was before. I dont have any of my fans running at slow speed at all. The lower fan is not working at all, although it will if I swap the harness from the the upper into it. Anyway, no slow speed is making the temps jump up. I did jumper one of the pressure switch harness but nothing happened. There's another pressure switch with 3 wires going into it, but not sure if I should be messing with it. Another thing is, that if I use the AC(which is not very cold) the temps rise faster and further but the are no fans running until it reaches a high enough temperature for the upper right fan to kick in at high speed, but by then the fan has to work harder. Electrical stuff is the trickiest in these cars. As for bypassing the lower I meant to simply disconnect the harness and wired it separately from the entire system...

 

Is there a mod that I can do in order to make the fans run at low speed once I turn the ignition on?