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I've been noticing lately my ficm holds 49 volts almost all the time. Every once in a while it does drop to 48.5. is it a problem to be over 48? This picture is after about 20 mins of driving
I'd say you need a thermostat. You should be closer to 192° as less than 185° it's burning excess fuel trying to warm itself above 185°. Lower that normal readings show a failing stat.
If it consistently runs above 188° then leave it, if it runs on the lower side, replace it.
I always saw 195 to 204 on my 2005 with the factory t-stat for the 10 years I had her. Diesels don't have plugs and are more efficient the hotter they run within parameters.