I had an end tank split open on a trip last fall. I had moderate temperatures going up long hills and replaced it. 10 months later, the new radiator did almost the same thing in cooler weather during an in-town commute. I bench-tested the electric fans and they worked well, need to test them in car after the new radiator is in. Any idea what the problem is or is it just bad luck?
There are three likely causes of the failure:
- Vibration or corrosion weakening the tank.
- An excess of pressure rupturing the tank.
- An inherent weakness caused by a design or manufacturing defect.
Since the old tank lasted some 15 years, it seems a bit unlikely that the first tank failed due to an inherent weakness – especially since the second one failed in a matter of months. That suggests that something has changed to cause the failures. It may well be a small cascade of failures, for example:
A leaking head gasket allowing gasses into the cooling system which raises the pressure then, then if the radiator cap goes and the pressure no longer vents through the cap, the tank could become the weak link in the system. Or,
A something leading to vibration stress on the tank, such as the weak or broken engine mounts suggested by @tlhigan transmitting vibrations through the cooling hoses or a loose radiator mounting allowing the tank to be stressed by radiator vibrations.
I think corrosion is unlikely in your case, since the coolant should have been replaced after the first failure.
Look closely at the way the radiator is mounted. Is there something that could be stressing the tank, say a hose attachment? That would suggest vibrations. Does the radiator cap look new? If not, that could point a finger towards the cap. You can test the cooling system for exhaust gasses and/or do a compression test to see if there is an obvious sign of a head gasket failure. One way or another, something is stressing the tank and needs to be found.