I like a good mystery as much as the next guy but I find this flipping ridiculous.

For a facelift XJS with 4.0L AJ6 engine, does anyone actually know the temp that the thermostatic switch in the radiator should turn on the electric fan? I have looked everywhere for this info but no luck. My repair manual mentions that the switch will turn the fan off at 90C (194F) but there is no mention about when it will turn it on. This bugged me

So I started digging on the internet, first locating the Jaguar part number DAC6794. I called around to all my go to suppliers here in the US, Motorcars Ltd, Coventry West etc etc but no-one has the part and hasn't had it for a long time. So I go to the Jag Classic Parts site in the UK and it says not available, contact us. So I duly filled in the request form and sent it off, receiving a reply the next day to say it's not available but they might have it in a month or two. Ok, so I sent back an email asking for the temp spec of the switch. The reply was, "sorry we don't have that info"

So I turned to some of the big chain parts suppliers, NAPA, Autozone etc. They all show the switch on their sites with prices ranging from $50-$100 but no specs. So I call all of them and they say sorry part not available and they have no info about the temp range!!

OK, so now I'm getting very curious and noting some of the manufacturer names, I gave calls to Standard Motor Products, BWD Intermotor and Wells Vehicle Electronics who all purportedly manufacture the switch. I spoke with folks in their tech departments and they ALL said the same thing........ Sorry part not available, sorry we don't know the spec and then they all said "we actually don't make that part it's an OE". One particularly diligent chap at Standard investigated for a few hours and then called me back to say sorry no more info.

I find this very odd, I can't think of any temp measuring device in the car that doesn't have a stated range, why would this be any different?

I can take a guess on when it should come on but I want to KNOW. I do know that my thermostat will start to open at 88C (190F) and will be fully open by max 96C (207F), so I would think that the fan would not come on till it got a bit higher but when?

There have been many posts on this forum about high reading temp gauges and cooling fans that either stay on all the time or don't appear to work at all, so it seems especially important to know what's what.

My fan works fine when I jump the switch so I know my circuit is good. I haven't been able to get the engine hotter than about 96C (207F), which is a good thing , so I don't expect the fan come on but I want to know when it will.

Yes I know that I could take the switch out and try to suspend it in some boiling antifreeze to test it but I shouldn't have to!!

Jovial rant over, enquiring minds want to know

Cheers,

Allan

 

I would think that the switch would be closed at anything above 194 and open at anything below. The first thing I would do is check all the associated wiring for continuity. You could always slide some cardboard in front of the rad to try to warm it up some more. My 87 v12 fan comes on anytime the a/c is on and when the temp guage reaches about the middle of its range.

 

I think normally these switches have a separate on and off temp with a gap of typically around 5-10C or more. If it was on off at one temp the fan would be continuously oscillating on off.

On my car the fan is only controlled by the radiator switch, the A/C state has no bearing.

Cheers,

Allan

 

usually the fan turns on when just over the point of the thermostat opening its designed too keep the temp gauge in the middle if not lower quarter. so i can safely guess if it opens at 190 its on at 195 personally i would get a aftermarket one that opens at 160. keep that jag cool!

 

I don't think that's the way it works on the facelift AJ6 cars. The engine thermostat is charged with keeping the coolant within the range of 190 and about 207 degF. The auxiliary fan is designed to provide additional cooling if temps exceed the high end of the range by a certain amount. I'm trying to find out what that number is. It must be at least 210F and could easily be as high as 220F.

Ideal coolant temp for efficient combustion is thought to be around 200F so I'm not sure you want to run a lot lower than that. In fact due to emission requirements it would not surprise me if Jag wanted the engine to run even warmer.

Quite rightly most people are sensitive to engine temps, which makes it even stranger that no-one seems to know the temp at which the fan is activated.

Cheers,

Allan

 

I have no idea of the specs of that particular switch, however, I have dealt with the HE V12 one many times over the years.

The V12 has 2 stats, of 88c, and fully open at about 100c, and the crossflow radiator lowers the temp by "approx" 15-20c by the time the coolant reaches the lower hose spout, which is about 82+/-c. All this from my days in the radiator repair industry, I learnt a lot, and owned a few V12's in those days.

The V12 switch is an 85c, NO on/off varying temp, and this is stamped into the brass casing. They switch the LH small fan (commonly called the overheat fan). This switch is quite accurate and efficient.

Most replacement aftermarket switches have this 5c on/off gap, which simply is not right here. One temp is either too high or too low, and I have messed with the alternatives for too many years, and always stuck with the OE switch, which, as you said is NLA, so s/hand units are pulled regularly when found on wrecked cars.

The bottom hose temp is more stable than top hose, as the top hose temp is always fluctuating with stat movement, whereas the bottom is more constant, which explains the reason thermo fan switches are in the bottom hose area.

 

Grant,

That is interesting in a number of ways. I'm guessing there must be significant differences between the V12 and AJ6 engines. Some AJ6 owners report that their switch goes on at around 215F and off around 195F. It sounds like the the purpose of the V12 switch is to help prevent the coolant from going out of range whereas for the AJ6 it seems that the purpose of the switch is to help bring the temps back into range if they exceed the range by a certain amount?

Also on AJ6 cars the switch is mounted at the top left of the radiator which also supports the theory. I'm wondering if there is a significant difference in the radiator design between the two engines?

Also my switch does not have anything stamped on it and it is definitely OE as I have owned the car since new, curiouser and curiouser

BTW, have you been watching the cricket? We don't get it on the telly here but I've been faithfully listening to TMS on my pc. Sounds like a rip snorter of a first test

Cheers,

Allan

 

Allan,

Yep getting it live on one of the free to air channels.

Looking good, and interesting. Long way to go yet, but any excuse to have a go at the Poms, HAHA.

Any excuse for a BBQ and a beer or 2 or 3, who's counting. The time difference makes for weird eating/drinking times, but fun is being had. Chilli crabs on the BBQ right now (it's midnight), and JD about to be opened, life's tough.

Jag content, just in case.

Mmmmm, top hose sensing, very odd and different, and I reckon the 'bringing it back from the brink" is sound processing.

My AJ16 has the sensor in the bottom of the LH tank, just above the lower hose spigot, so V12 sameness. It is a 2 stage sensing for LO and HI fan operation, as it has the twin thermo fans as OE.

 

Grant,

Yeah I know how rough it is, spent a good while visiting a mate in the Barossa, it's a hard life

Jagwise, interesting that they went back to mounting the switch at the bottom of the rad for AJ16.

Should be in for an interesting finish at Trent Bridge

Cheers,

Allan

 

I saw another thread about this switch and I remembered that I had not updated this one.

This was a bit of an ordeal but after getting no joy from JDHT, JCNA any of the Jaguar spares providers or temp switch manufacturers, I managed to find a bloke who was a friend of a friend who knew someone who worked in the Jag purchasing office. A little digging and I have my answer.

The OEM switch was made by a company called Elmwood (no longer making these types of products). It is a two position switch designed to switch on at 96C and off at 91C. Because of it's location about 1/3 of the way from the top of the radiator, coolant temps exiting the thermostat are about 100-103C (~212-218F ) before the fan switches on, this will show as about halfway or more between N and H on the gauge, which can cause a lot of anxiety for the owner!! However this is still in the 'normal' range as far as Jaguar are concerned. I finally got my engine hot enough and sure enough the fan switched on when temps at the thermostat housing reached 216F.

The main reason for designing it this way was emissions control. Higher head temps decrease emissions, high and lean was the order of the day.

The problem with this approach is if you are stuck in traffic on a very hot day, the A/C system will become useless after a while until the aux fan kicks in. As mentioned in many other threads this can be solved by modifying the circuit so that it cuts on when the A/C is on or change the switch to one with a lower operating range. Any M22 x 1.5 two position switch will do, there are literally dozens available.

Cheers,

Allan

 

Great post. I have had the exact same journey. Is someone able to post step by step instructions on setting up the electric fan to come on when the ac is turned on?