hi all, new to this site hoping for some answers. i have a 330-6 kobelco that boils every so often when under heavy load.fan belts tight,new thermostat,head gasket done bout a month ago,radiator clean.after about 10 mins work she puts about a gallon of coolant out the expansion tank which is cold,puts the temp gauge in the red then returns to normal again and works ok for hour or so till it does again.hs also blown the bollom rad hose twice.rad cooling ok as top hose hot bottom hose cold. any help would be appricated thanks in advance
I'd be tempted to investigate the possibility of an air pocket trapped in the block or head(s). It sounds like what you may be experiencing is the expansion of an air pocket causing the belching of the coolant. This is not that out of the ordinary, especially in certain castings where the highest point has no exit for the air to escape when being filled by coolant. In other words, the coolant can't displace the air pocket even under dynamic flow, so the air stays there until it expands due to heat. That's a WAG, btw...
Hi there. If your top rad hose is hot and bottom cold, then your water is not circulating. Both should be same temp. I would blame water pump if you had not mantioned blown rad hose. Sounds like something blocked. Are you sure rad is not clogged internally?
For a conventional rad that is functioning correctly there should be a temperature difference between the top and bottom coolant hoses of approximately 10-12 DegF (5.5-6.5 DegC). If the difference was substantially more than that I would be suspecting low coolant flow which would set me looking at the fan belts, tensioner, etc (which according to the OP are all fine) so my next port of call would be to pull the water pump and check the condition of the impeller. Next thought would be a rad that's blocked (or partially blocked) internally. For problems like this getting hold of an infra-red temp gun can take all the guesswork out of "what's hot and what's not". A cheap one only runs about $20.