does any one know what can be used to patch a radiator reservoir? I've tried the putty stuff and it didn't work still leaks.
Are you talking about the expansion tank? Is it a plastic type? Or the radiator itself?
I think the answer in either case is: Replace with a second hand or new part. The coolant is under pressure so if you do it right once the first time, it will last.
If you need to repair the tank, remember the temperature and pressure that will be present. I don't know if epoxy would cut it. In Australia there is a huge range of adhesives for construction and having a look at the range, find something that adheres to plastic, has a very strong bond. I would try and get a few layers on there as well. You'll also want to surface to be absolutely sparkling clean, so use the right process to clean oil/grime off the plastic surface.