You can get a Stant thermostat for less than half of the cost of a Jaguar part:
Jaguar XK8 Thermostat | Free Shipping | 2000 - 2002, 1997 - 1998, Stant, Beck Arnley

The light will eventually clear on its own after some number of drive cycles. You can also take it to a chain auto parts store and they can clear it for you, or you can buy an inexpensive OBDII reader and clear it yourself.

 

If you are just getting a thermostat, any of the local national auto parts houses can help you. RockAuto.com is probably the cheapest price, however.

Have you checked to see if your car still has the plastic thermostat housing that's notorious for failure? Some of the metal housing kits have thermostats with them that would save you some $. Welsh Enterprises is a source for them.

 

With summer on the way the light might go out on its own without even changing the thermostat, but I don't recommend that course of action. Right now your thermostat has apparently failed in the open position, allowing coolant to flow all of the time. The coolant warms up as it passes through the engine, then it cools off as it goes through the radiator. Since it is cold out, the engine never gets as warm as it is supposed to get. You may have noticed that your heater doesn't work as well as it used to. Once you get the thermostat fixed your heater will work properly again.

Once summertime gets here the air will be warmer and it won't cool the water in the radiator as efficiently. That will allow the engine to get warmer, and normally the thermostat would open up and allow coolant to flow. But since your thermostat is stuck open, the only time there will really be a difference will be when you first start the engine. It will take a little longer for it to warm up, but then it will run pretty close to the normal temperature since it is hotter outside. Because it's running close to the normal temp, your light will go off eventually. But then it will come back on next fall.

 

It is so nice to plug in a code reader (free at O'Reily AutoParts) and pull up the code for my amber check engine light. As I stated, the code indicated that the thermostat had failed. I replaced it today and found that the thermostat had failed to close completely and was slightly open when cold. I then went back and used the code reader to erase the code and turn off the amber check engine light.... Thanks to all. I love this forum...... Ron

 

Ron, you're one of the fortunate ones who had their t-stat (or wifes' t-stat in your case ) stick in the open position. What most often happens is it sticks closed, and the coolant never gets the chance to circulate through the radiator and cool, heating up the engine pretty quick and resulting in some severe damage...it can happen pretty quick while at highway speeds.

Did you at least reward o'reilys with a purchase of the new t-stat, or perhaps a fancy chamois for the weekend baths?

 

Yes I did buy the thermostat from O'Reily. They sold me a very high quality thermostat that looked identical to the Jaguar OEM. Jaguar's thermostat was $67.00 and I paid only $16.99. The specs state that it opens 60% wider, but it looked identical. Ron

 

Dude! You're a dude! For some reason I just assumed "Linda's Jag" was a female. LOL! Maybe I should join the forum using a woman's name and see how many of you visit my user page. Let's compare two relatively new members:

Linda's Jag has 33 posts and she's (he's?) had 35 visitors on his user page.

JagXK82001 has 24 posts, but only SIX visitors to his user page.

I'm no statistician, but it looks to me like members with chick names are more popular than members with dude names.

 

Yeah, I was like WT@#*& when Joycesjag started using his profile picture

 

Linda's Jag is LINDA"S JAG. She barely puts gas in the Jag let alone fix anything. She said "that is why she as me"....... Ron