Well my prob. is this. my truck (93 Ford Ranger manual 3.0lt, 6 cyl) seems to be overheating... when I drive it the temp gauge will get as high as the L (but usually between R-M) on the gauge... but then itll drop quickly down to the N, only to come right back up. Ive had to replace the water pump already so I dont think its that. Im getting woried about it but sometimes I just tell myself that Im paranoid. Am I?

 

Just a guess here, if you have an A/C + Heater, check to make sure that you actually reconnected the two hoses, from the Heater Core, on the right inlet and outlet.

 

Sounds like it may have air in the system.

 

Sounds like a sticking thermostat to me,

 

Just a thought. I had a GMC van with a similar problem, quick erradic changes in the temperature reading. Turned out to be a blown head gasket.