I've notice sometimes that my S.W. mechanical water temp gauge moves slowly up to normal temperature as the engine gets hot and other times it doesn't move at all until the truck had bean running for 15 minutes or so,then shoots to 180 (thermostat opening). Do i have a "lazy" thermostat or maybe a gauge problem? I have a small block 302, the thermo bulb is in the intake manifold water jacket near the neck...... coolant is normal level. Any ideas why this happens? Thanks.

 

Yep. Sticking thermostat. Not uncommon. When was the last time the cooling system received a good chemical flush?

 

But if I understand correctly, the gauge's bulb is on the engine side of the thermostat? Showing Cold would imply the thermostat is stuck open, then suddenly closes, not a common failure mode. Check for kinks in the capillary line to the gauge.

 

Gauge line has no kinks, haven't flushed out the cooling system but should put it on my "to do list"......along with a new thermostat. Spring is here, time to do a little PM on grandpa's 49.
Thanks guy's for your input!

 

An infrared thermometer is very handy to troubleshoot a problem like this.

 

I've got meter with a temp function, will do some checks next time I start it. Thanks