I can't answer your question directly, but I did have a Volvo temperature guage installed in my V90. It wasn't cheap. Because I bought 3 new Volvos in one year, my dealer sold it to me and installed it at cost, which totaled about $250. As I recall, the installation was somewhat involved, the dash apparently doesn't come apart very easily, and a tech gets something like 2 hours anytime it gets opened.

Also, for what it's worth, the ambient temp guage, as on most cars, was only roughly accurate.