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?
That's where you need to go next IMHO. Remove the cooling pack completely, split out all the component parts (radiator, hydraulic oil cooler, and A/C condenser), and give everything a thorough clean. Before you ask that pack cannot be satisfactorily cleaned in-situ because all the individual components are packed in so tight. While you have it all apart you should check that all the shrouds/baffles that direct air flow through the cooling pack are present and in good order. Of the two my first suspicion would be the radiator. If you want detailed information regarding remove/install of the cooling pack you will need to post a machine Serial Number. I see no less than 40 different models of 320C.
You can fart around with the thermostat but statistically speaking, it’s almost always the radiator.
Agreed, but you’d look a bit of an arse if you pulled the radiator and had it all opened up (top & bottom tanks are not bolt-on) only to find after all that effort it was the temperature regulator all along….
Seen plenty of questionable thermostats. Never tested one that I could definitively say was the problem. They are cheap enough that if I questioned it, I just replaced it. Radiators were always the problems that I have encountered. After coolers in front of radiator and hydraulic oil coolers just naturally trap dust and debris. There is a small space between them that is like a well where the debris accumulates. Most manufactures in the early models put a bolted on plate on the floor of the house that could be removed and let that debris fall out while you blew air through the front. Not so much anymore. Some machines now have the air side radiator on hinges and you can open them up and go to town with a shop vac. For my preferred method to clean radiators I use a half inch pipe with an air coupler on one end and a pipe sleeve and plug that has a hole drilled on the other end. It usually takes at least 15 CFM of air through that pipe to blow the crud out of between the fins. I would work both sides but the engine fan is usually a pain to get around. After all that is loosened I'll fire up the engine and see how much dust is cleared by the fan. Then I'll have the customer run the machine to see if the heating happens again. If so, then I'll pull the radiators and take however much time it takes to clean out the mess.