T&T: Engine temperature

[SID RUBIN]

I need feedback from the list on an recent observation.  Albin 40 with twin
135 Lehman's.  Owned boat for three years and always run at about 1700-1800
rpm.  Average SOG 7.75kts.  The temp gauges typically report 165-175 degrees.
Yesterday I cranked rpm's to about 2250 and after about 10 minutes noticed the
starboard gauge reading about 225 degrees.  Port remained at 175.  I
immediately returned rpm to 1700 and the starboard gauge dropped back to 175
degrees after about 4 minutes.  It continued to register normal from that
point at 1700 rpm.  I noted no steam, smoke or other abnormal indications from
the starboard exhaust during the high rpm run, and exhaust water flow was
normal.  Should I be concerned about what this event may be telling me?  What
should I do to further investigate?