My 2002 XK8 recently had a number of cooling system parts replaced:

• Reservoir
• Thermostat + housing + cover + cap
• Water pump
• Pipe outlet (AJ85885)
• Hoses (H-149 + NCA2213AC)

However, I've still had to occasionally add more coolant to my car, without seeing a puddle, etc. below where I typically park.

The other night, in a bad traffic jam, the temperature gauge shot up and the car began to smoke. Within minutes, I had the car pulled over and shut down. Left it to cool for 2+ hours, and drove home without further incident.

Took the car into the mechanic earlier today (who did the cooling system work) and explained the above. Right away he said it could be the fan assembly needs replacing, though ran a pressure test and check some other thing. At one point, he got the fan to run - not sure if that was due to disconnecting something, doing something with the computer, etc. I left with him saying it could be a few things, but he felt I should replace the fan assembly.

Considering he did get the fans to run, I'm a little skeptical of this. Are there any other issues that some here feel would cause this, which (hopefully) may be cheaper than replacing the fan assembly?

Thank you...

 

turn ac on, they should cycle.

 

The sensor that tells the ECM to turn on the fans is located in the cross over pipe that you replaced. I replaced my pipe recently and the fans would not turn off. Coventry West shipped me a replacement immediately which fixed the problem.

Do your fans come on with the AC on?

If I remember correctly from my problem diagnosis the temp sensor has a resistance of about 2k ohms in the 'call for fans' range. I have slept since then and worked a similar problem on the V8 Volvo so that might not be a valid number. This sensor also reports the actual temp to the ECM which can be seen with an OBDII to bluetooth converter and the free TORQUE app for Android phones. If you are seeing temps at or near 200*F and the fans are not running you either have a defective sensor or wiring connection problem to the ECM.

I was seeing temps in the 160 - 180*F range on a very cold day and the fans would not shut off.

Based on the limited information it is entirely too early to get the parts cannon out.

 

Just had a similar issue with the exception that I was blowing cooling system hoses off their connections. After replacing every sensor, fuse and reservoir cap (twice) I decided to bench test the fans. The first connection I removed was the left side and as soon as the attempt was made a rough surface was felt on the underneath side of the yellow and orange wire. (totally invisible unless removing the wire) A small section, less than 1" of wire was missing the insulation. I spliced in a new section of 10 gauge wire and now both fans are spinning freely. They come on shortly after turning on the car with AC on and are on full time at full operation temp. Took the car out today for the first time since the fix. Ride out was to make sure no revenue enhancement agents were present on the route and put it through the paces on the return trip. No blow hoses when shutting down.

 

Thank you all. Good information. Will try running the A/C tomorrow - will cold temperatures possibly cause the compressor (and therefore cooling fans) not to run?

When the mechanic did his tests, dis/re-connections, etc., some anti-freeze was lost. I neglected to refill this, and when I drove the car earlier, at one point the cooling fans came on.

Given that, I'm wondering if there is a "wiring connection problem to the ECM" as test point suggested as possible? If so, where is this wiring point, and does it relate to the cross over pipe where the sensor is?

 

Problems that first show up after work usually turn out to be associated with the work. First electrical issue I would look for is at the sensor connector and wiring. Second suspect is the sensor itself. The TORQUE app, a sufficiently capable shop diagnostic tool or a resistance chart is going to be needed to see that as a problem. The alternative is to swap out the sensor. Still got the old pipe/sensor?

With the AC on the fans will run continuously but may take 3 - 5 seconds to come on.

 

I tried running the A/C yesterday. The fans never came on, though I cannot tell if the compressor ever ran either, due to it being cold outside (I did set the system to "LO"/manual, so it wasn't dependent on the interior temperature). I don't even know where the compressor is!

My mechanic claims when he tested various things, he tapped on/hit the fan motor(s) and that also may have gotten it to run when they came on later that night.

Any further thoughts?

 

Big on testing rather than replacing parts. I would measure voltage at the electrical connector to the fans. Only after you are seeing battery and ground at that point would I go with a failed fan. Remember, there are two of them. Did they both fail at the same time?

 

With it about 30 degree outside and my AC on the fans cycled off and on for what it is worth.

 

Yes. Does that help in diagnosing a problem to replace (or not) the "fan assembly", like the mechanic called it? Not sure if he measured voltage or not yet.

I'm a little confused at what "seeing battery and ground at that point" - could you please explain? Thanks!

Also, I'm curious, would an old battery have an influence on this at all?

 

The control lead from the ECM provides battery (B+, 12.6v) to operate the fan relays. The fan relays provide 12.6v and ground to the fans. A battery with less than a full charge will produce all sorts of issues to long a list to provide here. Old is not the criteria, voltage under load, as with the headlights on should measure over 12.0v. If not fix that first.

I would still suggest that the problem is with the temp sensor or its wiring harness connection. Other than your tech's statement that the 'fan assembly needs replacing' not a single related fact has been presented.

Two fans are not going to fail at the same time. Neither are the two fan relays. If you cannot do these test yourself you need to find another tech.

 

Much appreciated!!! Thanks so much again. I'll let you know if I have any other questions...

 

Update...the mechanic told me he tested voltage, and it was good. He claims one fan came on after he hit it...

 

Revisiting this...

If possibly buying a used cooling fan, does it matter what year car (up through 2002) the fan came from?

Also, I see two variations of model # for these - MJB4270AB and MJB4270BB - what is the difference between these, and is either usable in my car?

 

In looking at new fans, I see SNG Barratt has two items available, both "AB" variant models - one with an *, one without - and there's a big difference in price:

SNG Barratt - The Ultimate Jaguar Parts Specialist
SNG Barratt - The Ultimate Jaguar Parts Specialist

Any idea what's different in one vs. the other?

 

In looking at new fans, I see SNG Barratt has two items available, both "AB" variant models - one with an *, one without - and there's a big difference in price:

SNG Barratt - The Ultimate Jaguar Parts Specialist
SNG Barratt - The Ultimate Jaguar Parts Specialist

Any idea what's different in one vs. the other?

 

The people at Barratt are great. Why not just call them and have them explain? They are not some craiglist operation trying to rip you off.

 

I believe that the '*' indicates an aftermarket part. Without indicates an OEM part. Do the prices sorta confirm that?

 

Thank you.

Any idea re used parts - will a fan taken from any year XK8 made up to my car's year (2002) be acceptable? Does model # "AB" vs "BB" make a difference?

 

I would verify by seeking parts from a couple of on-line sources for both early and late model years but I would think that the fans have not changed across the '96 through '02 run. Unless you get into electronics the extension changes are mostly compatible.