Test by measuring the actual engine temperature vs. the gauge. A non-contact thermometer from Harbor Freight is about $25 or so and perfect for troubleshooting problems like this.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC