ive had cooling problems at one time or another with all three of my trucks. when i replace a thermostat i first check it in a pot of water with a direct reading thermo, meter to see if it opens as its supposed to at the temp. its rated for. next i drill a 3/16ths hole in the thermostat which eliminates it from getting airlocked. since i have three new rebuilt engines they all got new water pumps and hoses. i then got all three radiators recored. since then i have had no more cooling issues in my trucks. my 40 runs warm when it's hot out and stopped in traffic. i have shot it with an infared camera after an hours run not long ago and when the temp gage was reading + 180 with a 170 thermostat the camera showed that the water was only 170 being discharged into the radiator. three quarters into my 630 mile run back from southbend it was running about 190 and i got concerned and pulled over and added some coolant, it only took about a quart and was relieved. it was hot that day and i was just about to crest the last ridge. after that the day started to cool down and it was down hill for a while which then it returned to what i call normal.

since yours is heating up so quickly is the thermostat installed correctly?

40 GMC 250 STAKE/FLAT BED
1951 Chevy 6100 Dump
51 GMC 350 ENGINE 500/500
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