Hey Everyone,

Another day another problem! Ha, I still love the 03 XKR but last night she really worried me. The last couple of days I noticed that the fans were running after the car was off. This does happen from time to time but had not happened since I can remember. I monitored the coolant level and temperature gauge closely and had no issues, until last night. On the way home, the temp gauge started rising above the midpoint. I immediately turned off the road and popped the hood to wait for it to cool down. Had to do this twice on the ride home and thankfully made it back without overheating I hope.

My thinking is that this has to be a stuck thermostat. Wondering what you guys think? Also, I have not replaced a thermostat on a car before but have been reading that is is pretty easy. I am thinking you drain the coolant and then replace the thermostat and gaskets. Is there anything that I am missing here or any advice or tips you would have? Looked online and see that there are a few options for thermostats and my local Advanced Auto Parts indicates they have one in stock which is a very cheap unit, maybe $15, and then there are others that I am finding that are $25-50 but not in stock. Would you feel comfortable using the lower cost thermostat?

Thanks so much!

Corey

 

Replace the thermostat with an OEM one that has the correct shape and weep hole to allow trapped air to escape. Use coolant meeting JLR specification such as Dexcool and bleed the system according to the instructions in the Workshop Manual.

DO NOT rely on the instrument cluster temperature gauge to determine coolant temperature as is does not change between 95 C and 128 C. Use a smart phone and the Torque app to communicate with the PCM through the OBD port via a Bluetooth adapter.

 

Other theory is the water pump. They are cheap too, and it might be a good time to replace as the coolant is already drained.

Of course, if any of your radiator hoses collapse when the engine cools, now is a good time to replace them as well. Throw in a new overflow cap for good measure.

Double check these dreaded valley hoses. One of them attached to a pipe upfront. Check for overall condition, so not soft or ballooned out. Those are a lot more work to replace...

If you need to drive again (not recommended), remember that heat is heat, so turning your heater on full heat acts as a secondary radiator and can only help the situation.

Best of luck, keep us posted.

PS: for coolant, make sure you use DEXCOOL (orange). And do not mix with other cooling fluid as some will produce a gel and clog the system. Definitely double check what is there already to be sure.

 

Seems general forum member opinion if this is on the 2003 4.2L XK8, is to replace the entire cooling tower plastic assembly. A new Stat and Temp sensor are included with this part. Installation is documented in previous threads. Part # AJ89486. The sensor is $25 & Stat with Housing is $45-50. separately. You do not want to struggle with just stat into your housing. once you look, you will understand. Not conventional stat. That plastic is OLD... REPLACE it now .

 

Hey Guys,

Thank you for input. It is strange, I think my thermostat housing is actually aluminum. I do not have any history on the car but the piping at the front of the engine bay with coolant hoses running to and out of it are aluminum. I was assuming that this is where the thermostat was housed.

It pretty much looks identical to the housing in this video from a 2003 XJR.

 

The 4.0 supercharged engine has a different thermostat housing than the normally aspirated 4.0 unit.

 

Its weird though, I have this same set up on my 2003 XKR. Nothing plastic. Doing more research it seems to me that the XK8 has the plastic thermostat housing and the 4.2L XKR has aluminum. This is a relief for sure. The picture below is exactly what my engine and thermostat housing looks like. Seems like it is a pretty easy procedure to unbolt the housing, remove the thermostat, and bolt it back up. From what I have seen online, there doesn't seem to be any gaskets required either, just the rubber sealer that is part of the thermostat unit.
https://upload.wikimedia.org/wikiped...y_%2830%29.jpg

 

I sent everyone down the wrong (mental) path earlier with the XK8 advice. The XK8 has the plastic parts. The XKR has a different, mostly metal setup.

 

No worries fmertz! Appreciate your input on things tremendously! I ordered an OEM replacement thermostat that should arrive on Christmas Eve. Hoping to give myself a Christmas present of a fully functioning, well nearly fully functioning, XKR! Will let you all know how it goes and thank you again for all of your help and suggestions.

 

The collapsed hoses lead me to think that it is a stuck thermostat. It happened on my XK8 when the thermostat stuck, and then when the engine cooled the vacuum sucks down the hoses. I disagree that the hoses are bad when they collapse - it actually means they are holding tight, and when the coolant cools the hoses pucker. Very easy DIY fix.

BTW anyone who has not replaced their (plastic) cooling pump with the metal one on the early XK8s SHOULD NOW. They are time bombs and will indeed blow a blade at some point - just a matter of when and you'll probably be on a long trip.

I buy my stuff from Terry's Jag and have never been disappointed (no proprietary relationship). DON'T buy Jag parts from Autozone, O'Reilly's or other discounters.

 

Just wanted to follow-up with everyone and share some good news. The issue that I was having with the fan staying on long after the car was shut off and the subsequent near overheating was in fact the thermostat. I replaced the thermostat which was fairly straight forward although getting the Torx 30 bolts off was somewhat challenging. I ended up using a Torx 30 allen wrench and managed to get them off. Replaced the thermostat and she ran great with no rising of the temp gauge over the mid point and also the fans shut off immediately after turning the engine off which is what happened 99% of the time before this issue cropped up. It was nice to have a fairly straightforward and low-cost fix to what could have been a seriously damaging issue.

I just wanted to thank you all again for sharing your input and insights. It is very rewarding to keep our beautiful Jags running on our own accord and it surely would not be possible with out the help of the members of this forum. Hope you all have a great night!

 

Keep tabs on the coolant for the next few weeks.
Very difficult to get it full on the first try. Turn the heater on, I know you are in Florida, but for a little bit, if nothing else to get full circulation in the system.

 

Great advice, I will definitely do so. So far, no low coolant warnings have come on but I should check the reservoir just in case. Thanks!