You can buy a OBD2 compliant scanner online from a company called Innova. These scanners are capable of reading all car codes on every vehicle sold in the US after, I believe, 1998. The model is Equus 3030. It worked fine on my Volvo S80. I was able to read the problem codes and reset the check engine light.
It is impossible to change the thermosate. The thermostate is built inside its housing. Therefore one would need to change the entire coolant thermostate housing. The major problem with this obsoutle vehicle is that this part can not be found. The last resort is to check out your local junkyard and you should tons of Lanos. Yank one from there. I have remove two housing so far and as soon as they are installed they crack. If any one come across where they can be puschased brandnew....please drop me a line. at nomi4hire@yahoo.com I have one sitting in my driveway and it needs a housing. Nomi www.partsgeek.com carries the housing