I have had constant cooling issues with my XJR which, I suspect, led to a blown gasket a couple of years ago. Anyway, she still seems to run on the hotter side compared with the numerous reports I've seen in multiple threads here. Over the past few years I've had everything replaced in my cooling system - radiator, thermostats, hoses, expansion tank, water pump etc. She gets very hot in heavy traffic or climbing steep, long gradients (mountains) - get's very close to 221°F (105°C).

The two things I wonder about, usually in the small hours when I can't sleep, are:

1) My original cooling fans might not be nearly as efficient as they used to be? I wonder how much cooling ability they actually loose?

2) Maybe my aftermarket brass radiator is not very good? (8 years old, reconditioned 12 months ago)

 

A brass radiator?? Do you have any pictures with it out of the car?

I often wonder what can be done to replace the stock cooling fan motor with a new brushless motor without too much fabricobbling.

 

I can't imagine the fans even existing make much difference if you're moving at a reasonable speed so there's airflow through the rad.

I'd be suspecting the non-standard rad doesn't allow as much coolant and/or airflow resulting in it removing less heat from the cooling system.

 

Unfortunately, I don't have any photos of the radiator - it's black and doesn't look like bare metal.

The replacement fans cost USD$964, so not something I want to jump into if it's not going to make a difference.

 

Most of the overheating occurs when I'm crawling through traffic, so I was actually leaning towards the fans rather than the radiator. I did find a few aluminium radiators for a reasonable price - but have no idea if that's the problem. Also, as mentioned to @Addicted2boost, sourcing a genuine fan replacement is about USD$964 and a genuine radiator is USD$1055.

 

Ahh, I hadn't seen you mention traiffic, apologies if I missed it. I know the fan control gubbins has high & low speeds for each fan. No idea if it'd throw codes if the high speed isn't working, but that has to be worth a look if you've not already done so? I've seen diagnostic instructions on this forum before. From what I recall it goes off engine temp AND AC pressure rather than simple thermoswitches in the rad.

 

Thanks for the suggestion, I checked the fan function first as I was caught out by this some years ago!

 

While looking over this thread, I imagined your issues and what methods I might
attempt to determine the cause/s. If my radiator was ascertained to be circulating
the coolant and my fans were cycling on and off as intended, what would I check
next? The thought occurred that perhaps the water pump was not circulating the
coolant at the proper rate, or that the thermostat was not operating as intended.
I remember an SS396 where the thermostat would occasionally stick, and cause
it to overheat which took me a while to pinpoint.

 

actually 221*F isn't that bad when crawling in traffic. Coolant will raise the boiling temp, so will pressurization. So you do not appear to be closing to boiling over.

Need to check to see if both fans are working; are you getting any knocking climbing grades? Using high test gas?

Maybe change the coolant and drive . . .

 

I have an s type r. Same engine and cooling pack. Every two years i take off the bumper cover and hose out everything. It makes a nice difference. If you want to diagnose an easy way is to get a cheap box fan. They are easier to get to grill height. Take a drive to get warmed up then park in driveway or near an elec outlet. Leave in park and put the fan on full in front of the grill. If you get a nice temp drop then your engine fan may be suspect. If not then probable debris in cooling stack. The radiator is the last in line to get the airflow so the intercooler and condensor need to be clean as possible. An outlier would be high condensor temps when using ac but that would also affect ac performance. Just noticed you have 2001 xjr. Should be same cooling arrargement but i dont know about engine

 

A coolant line flush with filtered water and ran without the T-stat 50 miles, heater matrix on open on hot! Evenings best.
Check the whine of the intercooler pump with ignition on.
Fresh 50/50 orange Ford spec coolant mix and a good old burp, or vac fill.
A new T-stat, and blast outside the other coolers behind the grills with compressed air if possible, jet washing with a bit of care might clear debris.

(You checked for no lines crossed?)

I used to commute in my R and on a good few occasions ran it into the both fans on high speed, which are very efficient if the bonnet is popped. It needs to be all working well in high temps for a happy engine.
I did notice Shell V-Power gave the engine a better protection from pulling timing. It should be fine in high road temp traffic.

The RealGauge offered by our forum member is a great tweak.

https://www.thejagwrangler.com/xk8--...realgauge.html

 

Hi Randy, I've had the thermostat and water pump replaced since this issue began so, while not impossible, it's extremely unlikely - especially given that I have tested that the fans come on at 95/105°C (203/221°F)

 

Hi Jim, thanks for your comments. I'm using 98RON which is, I believe, equivalent to your 93 octane. I don't have any knocking when the car is under load.

Maybe I'm just being paranoid after dealing with a 2 year period of overheating and coolant loss that resulted in a blown head gasket - I started to get obsessed with monitoring the coolant temp (OBD2) all the time.

 

Thanks @Sean B and @scottjh9 - I'll look into clearing any debris from the intercooler and condenser! I currently have my OBD2 sensor, it connect automatically every time I'm in the car and has an alert set for 221*F. The coolant was flushed and replaced with Type A (Ford orange).

 

Maybe try another expansion tank cap as it’s possible that it doesn’t hold all the pressure.

 

You can test the X308 cooling fans that they both come on to highest mode

On the X308 it does have a similar fan control relay module to control both fans which in turn is commanded by the engine ECM

You should have a coolant temp sensor ( and not a temp switch as in the X300 ) that can be removed and tested with a hot water bath )

The target temps on the X300 inline 6 engine are low mode 86 C and high mode100 C

You need to confirm that both fans run high at your engine's high need

Just need to see high mode

The fan relay control module can be mounted upside down , connector has to be on the bottom

The power contacts inside ( sealed ) can be corroded not delivering the current to properly power the fan motors

Both these fan motors have a ground terminal somewhere

On my X300 , it was full of water as mounted connector side up

Your X308 fan relay control is black in color and not white for the X300

There is a coolant hose misroute the Motorcarman has seen plenty of and has the details



Module location under car left front wheel

 

@Parker 7 thanks for the tip, I've already tested my fan operation and they come on 95/105°C (203/221°F). This was one of my first troubleshooting tests due to problems with this in the past.

 

95/105°C (203/221°F)

In my judgement this is high , is there a reference that these are the design

If so the fan control relay module power contacts can be compromised limiting your fans effectiveness

Counterfeit fuses that limit the current without blowing ?

 

Hi Parker,

Yes, these are correct, see page 37 in this document which shows the following:

 

Thanks for the reference , do you have a link ( for the library ) other than what you had as this takes me to an advertisement

I do not have the X308

Quality known brand fuses ( or swap with the like cabin blower fans ) would be a cheap try other that a load test lamp on the fans or purchasing anther fan control relay module

There are 2 fuses in the system

Will be at dialysis center for a while becoming one with my purity