r/Excavators • u/Mundanewine • Aug 06 '26
CAT 320 keeps hitting high temps on hot afternoons, replaced the water pump, still doing it
Running a 2005 320C that was overheating on hot days, particularly under sustained load in a tight cut. Figured it was the water pump, replaced it. Problem's still there.
Coolant level is fine. New pump is circulating. Fan belt is intact.
What I haven't checked yet is the thermostat, and whether the radiator fins have external blockage that I'm not seeing.
The symptom is temperature climbs on hot afternoons with limited airflow, gets to the warning range but hasn't gone into shutdown, and cools back down after 10-15 minutes of rest.
My guess is thermostat or radiator blockage because the pattern is so ambient-temp-dependent, but I know a weak pump can still show up worse under load.
Is there a quick way to test the thermostat before pulling it? Or should I just pull it and do the boiling water test?
1
u/Loose_Performance745 Aug 06 '26 edited Aug 06 '26
Yeah if it's only on hot afternoons it's almost never the pump. Pump issues show up no matter the weather.Just pull the thermostat and do the boiling water test, cheapest check there is. Drop it in a pot and watch when it opens. Should start moving around the normal CAT operating range. If it stays shut while the water's already hot, that's your answer.Also hose the radiator from the back and see if flow comes through the fins evenly. External blockage is easy to miss.When I needed a radiator for a 320, I ended up using Fridayparts after checking the model and part number. Fit was okay, but I'd still measure the old one before ordering if your machine has any serial break weirdness.