If everything else is working, what you describe could be the result of an issue with the head or gasket. (I know, that's pretty unlikely for an OM61x). Is there any pressure in the system when cold? Also, if the needle moves very rapidly, that indicates an electrical problem - NOT a temperature problem. It should take 15-30 seconds or longer to move from 95c to 105c. If it's only a second or two, time to check electrical connections...