I'm posting in the XK section with hopes to get some other opinions on my persistant engine/cooling system issues. 2006 4.2L, N/A, 63k miles.

This all started in January with cooling system problems, that turned out to be the usual plastic crossover assembly broken, dealer replaced that under warranty. Then everything seemed fine.

Around April/May, the weather warmed up, I realized that around town the engine was pinging noticeably (and I do run 93 octane). I found a TSB for the 2006 XK/XJ 4.2L pinging on light throttle. Had the dealer do that flash. They said if the pinging continued, they suggested a fuel injection cleaning.

That seemed to work initially--temps were in the 80s and all seemed well. Then as the weather warmed I started to notice the engine fan was running on after I shut off the car, whenever I do city driving in ambient temps over 80-85.

Long story short:

• My coolant temps as measured with OBD2 show 195 F when cruising, spike to 205 F when stop and go or idling. Without A/C they stay at 195 on the dot, with the A/C causes them to rise to 200-205, but these seem fine to me.
• Fan will not run on when I drive in < 80 F ambient even with A/C, i.e. on the drive to work in the morning (6 miles city). Also, ECT stays at 195, IAT about 80-90 F.
• In 80+ ambient, I can drive 2 miles, park, and the fan runs on a slow speed for 4 minutes after shut off.
• If I drive 150 miles on the interstate and park, fan won't run. From what I can read on my scan tool (ECT and IAT, but not oil, trans, or fuel temp) the IAT going over 100 F seems to trigger the fan issue.
• If I keep the A/C off, I can drive 20 miles in the city and have no fan running issue. But I park, come back 5 minutes later, move the car across the street, and the fan runs for 4 minutes. This seems to confirm the IAT theory, that it's heat-soaking in the engine bay.
• Along with the IAT causing the fan to run, it seems that my engine pings like crazy whenever the IAT goes over 90. But everything is factory with the intake ducting. Stop and go I see the IAT up to 120-130, and that pings horribly.

I know that the manual says the fan *can* run on after shutting the car off. But everyone else I've talked to with an XJ says their fan *never* runs after shutdown, even in 100F summer heat. I've also heard from several people that the fan run-on is usually when there's a thermostat issue. I feel like my t-stat is working fine based on the ECT readings.

The other thing: this PCM flash the dealer did for pinging, I read one blurb somewhere that the 4.2 PCM programming was changed to run the fan on to prevent heat soak. Can anyone confirm this? I feel like this issue is just going to drive me nuts, and I guess the only option would be to revert to the old PCM flash and see if it went to keeping the fan off?

Thanks for any advice, and to anyone who read this whole book!
-Michael

 

I had similar behavior, intercooler pump had failed. Clue was the fuse (under the hood) was blown. Replaced pump pinging stopped and car cooled off.

 

No Intercooler on a N/A Car.

My car (and many others) had Fan Run-On with a Bad Thermostat.

 

Yeah, no intercooler or pump on my car. But I do have the little electric aux water pump as part of the HVAC. I wonder if that ever runs at idle in hot weather to assist the engine pump? Supposedly my aux pump was replaced by the dealer for a low-heat output condition. This past winter I had no issues with heating. Started blowing hot air just 1-2 minutes after starting. But the housing failed after that, so it's possible some plastic got stuck in there. I will try and check that.

I know everyone keeps telling me the t-stat--and I know these cars had issues with the t-stat failing even when new, but I just feel like the temps are perfectly in line with normal operation. I could try, but throwing $50 down the drain?

This weekend I'm going to try and pull the radiator and backflush, and clean the matrix. I know the condenser is clean on the front side, but it's just so temperature dependent I feel like something is off. This car can't seem to cope with anything over 80F. Below that and it operates flawlessly.

 

The only time i experienced pinging, and i always use 92+ octane fuel, was when i had a lean condition caused by air/vacuum leaks. It eventually triggered a CEL for exeeding the +15% LTFT level (IIRC) but not for the first few months. Check your STFTs also.

 

When I started the car this morning, LTFT were -5 and -9 for bank 1 and 2, when I returned home and idled, got -7 and -13. Negative means it's leaning out the mixture?

Noticed it did have light pinging when the IAT was only 86 degrees, just drove 3 miles to go the store. But then on the return, car had sat for an hour, IAT was 110 on startup (obviously the sensor heat soaks being part of the MAF), but dropped quickly to 95 once I started moving down the road. Fan did not run on this trip.

 

The fan is going to come on a lot more often then it did before. That is one of the things changed with your reflash. It is to address the fuel perculation after short runs.

 

Really? So that explains why it does it mostly after short city trips but not after a long highway drive (well, I have gotten off the highway after driving 15 miles and it kept the fan running... but usually it won't run in that case).

Can the dealer revert back to the old PCM programming? This fan is going to drive me out of my mind, and I'll either re-engineer the fan circuit so it can't run with the key off, or I'll get rid of the car.

Just my opinion, but would have made a lot more sense to have the fan run faster with the car on, rather than for 4 minutes after the key was turned off.

 

The only way to reprogram back to the old software. This would mean you have to find someone with an IDS that is only running Legacy only without SDD. We keep one computer set up this way to work on older cars. It can be done as I have actually had a customer with your same complaint. They requested web try to install the old software which we were able to do.

 

I really appreciate your help! I'm glad to get some confirmation that nothing is actually wrong with the car, and my fan is running because of the PCM recalibration. Was going to go nuts with people telling me the new thermostat was faulty!

So maybe an independent Jag shop can do the reprogram back to the old? I'll have to ask around. I know there's one shop nearby.

But unfortunately, this will bring me back to my original problem of very bad pinging. The flash did fix a lot of that (but not completely). Have you seen this issue on the 4.2L and is there some kind of other solution? The dealer said to run Techron, but I know that's not going to do anything to actually fix the issue.

 

There is another thread currently addressing 4.2 problems. Look for "Spark Issues?". He claims running 3 cans of BG44K and significantly reduced preignition.

 

Thank you! I will look for the BG44k and see if it reduces my pinging.

JgaXkr, before I go trying to un-do the PCM flash, what were the symptoms of the "fuel percolation" you mentioned? Did that happen when you stopped the car after a hot drive, come back a few minutes later, and when it restarted it almost stalled before running?

 

I don't recommend you going back to the old software. The fans are addressing a known fueling issue. The other thing is it also addresses the ck engine P0128. If you replace an O2 sensor you will also need to reflash the ECM.

 

What you may have takes some experience to spot...the thermostat has a diverter on the back of it that closes the bypass in the thermostat housing when the thermostat opens. If the housing bypass seat is damaged, the system will undercool by allowing the hot coolant to short circuit through the bypass circuit. Look for damage inside the housing.

 

Yes, that was the issue I had back in January. I actually had to pull the thermostat cover myself and show the dealer the broken plastic pieces because they were content to just keep replacing thermostats. The entire housing was replaced under warranty.

When mine had that problem, I drove it about 30 miles in 60 degree weather, the engine fan was screaming when I parked (temp gauge still only indicated normal... we all know how useless the gauges in these cars have become).

Right now my engine temp is completely normal--no more than 205 F in hot city traffic. But get the ambient over 80 and the fan will run on low for 3-4 minutes after shutdown. It makes sense now that JgaXkr explained it. I think I will probably take his advice and leave it with the updated PCM software since it fixes other issues.