Volvo: 1990 Volvo 240 Station Wagon, coolant temp, volvo 240

Question
Over the past year my check engine light has been coming on with the code 123 on 11/13/08 I had the coolant temp sensor replaced by my mechanic.. About 6 weeks later, the check engine light came on again. I checked the code myself and once again it was 123.  I asked my mechanic to check it, and he agreed it is 123.  He said it can be other things beside the sensor, but now the code won't clear and I decided for now not to spend any more money on that issue. Since in the past week my front right strut (insert?) is leaking and was told it would cost about $500 to repair I am thinking of getting rid of the car.  My questions are does that price sound right for the strut job? Do you have any suggestion on the recurrent code 123?   I forgot to mention that for many years I also get code143 (Knock sensor was replaced in 2005)
I appreciate any feedback.  Thanks Janis

Answer
Janis,
Well $500.00 is high. My shop does things like that two strut inserts installed about $375.00. That is if there is nothing else wrong that would need repair.
Since the code for coolant temp returns, try to replace the t/stat. Maybe yours is faulty and not allowing the engine to reach operating tempature.