I have a 2001 4.0 XKR. I read somewhere that the cooling fans come on at 210 or 215 (F, not C) I would like for mine to come on at a lower temp (195-200?). Is there a simple thermo switch that needs to be replaced or is this a programmed function in the ECU? If it is in the ECU is it something that can be changed (via programming) or manually over-ridden?
Thanks,
Adam

 

There are 2 controls for the temp. One is the temp switch in the water line. It is not adjustable. The other is the ECU it automatically turns on a fan when the AC compressor is running regardless of temp

 

Thanks for the reply.
Do you know if the temp switch is replaceable?
Anyone have a pic or diagram of one on a 4.0 XKR?
Adam

 

The temp sensor is certainly replaceable but there are not temp specified resistances available. The sensor do have a factory tolerance of a few ohms but you might get tired before finding one to your liking.

What are you trying to accomplish?

XK8 / XKR / XJ RealGauge - TheJagWrangler

. . . . for the answer to a maiden's prayers.

 

Well let's think about this. The link test point provided explains it all, but building on that: the car reads the resistance in the temp sensor to determine temperature of the coolant. Read how one uses the pot to calibrate the thermometer.

You know what, rather than even brainstorming using fixed resistors added to the sensor circuit ( I was actually going to go down that path, way to many contingencies) just hook up a relay to turn the fans on whenever you want to, put the switch in the cockpit. Hell if you add the real guage you will see accurate coolant temperature with a glance.

 

Why do you want the fans to come on at a lower temperature?

 

That is not correct. The fans come on at about 190* F.

 

A couple of reasons..
1. Some advocate the use of 170 degree thermostat in an attempt to improve induction temps via intercooler. I would think that since the radiator has a predominatly seperate flow for the intercooler that running the fan earlier (particularly in traffic) would be a better solution.
2. A 185 to 190 water temp will exert less pressure on the old hoses than the system pressure at a higher temp.
3. Safety margin.. In a few years it might be hard to replace an overheated motor.


Anyone use a seperate pusher fan in front?
Anyone using the Evans waterless coolant?
Anyone have a diagram or pic of temp sensor location?


Thanks
Adam

 

I have to say that if you're concerned about the integrity of the cooling system, then you really should address that in preference to trying to mask a potential issue with a lower fan temp.
If you're really worried about cooling system pressure then consider a waterless coolant that doesn't pressurise when hot.

 

Sorry for all the questions..
Avern1 references a "temp switch" and Testpoint & Jonken refererence a "temp sensor"...In looking at the RealGauge info it appears the temp gauge uses a sensor not a switch. Am I correct to assume that it is a computer (or other logic circuit) that turns the fans on/off (based on temp or A/C use) and not a seperate switch?

 

Bladerunner..I agree on the waterless coolant. I have seen it used in off road vehicles...when chafing or debris caused a small leak in an otherwise new hose, the leak was easily stopped with duct tape since waterless has little if any pressure. With no pressure there is also no sudden spray/loss of coolant and being out of the race. I am not worried about the integrity of my cooling sysytem so much as I just prefer lower pressure in general. Waterless is nearly no pressure but expensive. So i guess my reference to "old hoses" was more of an afterthought and lower induction temps was primary

 

OK, found the answer. Sensor provides a declining voltage to ECU that in turn cycles on and off cooling fans based on temp or A/C use.


Thanks for your help! Really enjoying this site.

 

avos uses Evans (different jag model though).

 

Maybe I am misreading here. If you modify the voltage signal sent to the ECU for the purpose of turning on the cooling fans early, you are sending the ECM false engine temperature data which might affect fuel trim, EGR action, timing advance, etc.

It might make sense to build an elegant parallel system to allow you to manually and/or automatically run the fans at settings that you select. In this manner, the integrity of the original system stays intact and both are a secondary backup for each other. The only extra work will be installing a separate sensor. This is not particularly difficult and would probably involve placing a T in a hose at the thermostat housing.

You will be able to see the results of your modification without changing other variables. Also, get Real Gauge, the best mod I have ever used.

These cars tend to run on the cool side already. On the highway in hot weather it takes close to an hour to heat my oil to max temp.

 

if you are concerned about the old hoses, that is your little voice telling you to replace them, cheap insurance.

these engines are commonly available. there is a reputable company in California that sells a completely rebuilt, guaranteed replacement for around $3700. of course you could always send your motor to Jasper for a rebuild.

 

Thanks WhiteHat. Good to know about the engine availability. Previous owner my have recently replaced hoses as they look pretty good.
I like your suggestion of a parallel system. Pusher fan tied to its own thermostatic switch should do an excellent job and as you said provide some level of backup to the factory fans.

 

Yes. Not good. May cause codes, too.

 

Thanks for the input.


Appears to be some variance from car to car. My fans (2001 XKR) are on at 205 and off at 195 yet 'test point' mentioned his came on at 190.


MAF, inlet temp and O2 sensors should govern trims, so not to worried about codes.

After reading JTIS ..the number one reason for using a sensor w/ ECU may be that by doing so it provides a simple way to monitor coolant temp and contrast that with Air Conditioner demand. That would allow the ECU to shut down A/C at high coolant temps and protect the engine from overheat.


Going to back burner this for now. Off to the next project!

 

Well, you can hope.

Is your 4.0 one that needs its timing chain tensioners etc changing?

 

Hello JagV8
New tensioners installed a few weeks ago. I used Lincoln LS tensioner with cut down bolts. About two days before tensioners arrived (just over 75,000 miles, left hand drive) the bottom shoe of the passenger side tensioner came off and followed the chain around the exhaust cam gear. This caused it to jump a tooth. Luckily it was just one tooth. I think if it had jumped two teeth then valve/piston damage would have occured.
Symptoms were check engine light with a loping idle (like a slow gallop) and low idle speed. Otherwise drove fine. At first I thought mis-fire, coil, fuel injector etc.. Drove home (10miles) pulled the codes. Several codes all from the same bank. Lightbulb moment! Pulled valve cover for verification.
Replaced tensioners and moved chain one tooth back. All the timing flats on cams from both sides now line up parallel to head. Leak down check and compression checks all uniform. Finally a camera inspection within the cylinders confirmed all valves/pistons were untouched. I got very lucky! Runs like a champ. I'll post a seperate page to this experience with photos later.