My 1993 240 Sedan has a rather odd engine temperature "issue". When you start it up, it gradually makes its way up to normal operating temperature (it takes awhile though, about 10 mins.). After about a half-hour of driving, the temperature will drop to about halfway to where it should be and stay at about that point. I changed the thermostat and coolant temperature sensor and nothing so far has worked. Could it be a problem inside the instrument cluster? Thanks in advance.