Overheating

Had similar problem expecting either small or huge bill.
1. Check all connectors (broken/loose) - garage do that & not costly
2. Pipes (split/perished) - garage do that & not costly
3. Take coolant bottle off & check for leaks
4. If milky oil - probably head gasket - water getting into oil - overheating
BEFORE you buy expensive radiator etc ......
My problem was the connectors - cost me £40 (about 30mins work)
Hope that helps - sure far more experienced Jimny owners out there who can help. Good luck
Toots!