Dont let him sell it, just take the keys off him and drive off in it and tell him something like its the RR and you or nothing at all
If its overheating under load then the first thing you would need to check is whether the system is pressurising. When it starts overheating, immediately stop, get out and check the two hoses going in and out of the radiator, if they are rock rock rock solid then i would have to agree with either head gasket or cracked cylinder head as this was what I got when I had overheating problems with my DSE.
If you find the pipes arent rock solid and you can squeeze them but they are still firm I would check the water pump and the rad. After my overheating problem I had an after market water pump and rad fitted. This was a BAD move, the water pump had a dodgy bearing anyway which meant it completely failed on me, leaving me stranded with coolant all pouring out. So a new genuine pump was fitted and I thought all was fine until sitting in traffic the needle started to climb again. After much research and anguish and thinking about selling up I read about an internal baffle within the radiator. My after market rad didn't have this baffle, which basically meant coolant went in the top of th rad one side, flowed along the top, not getting cooled at all and then came out the other end at the same temp. I replaced the rad with a new genuine one (which only cost like £40 more) and my overheating problems dissapeared.
If the rad is old but genuine then the baffle might still be there but the rad might just be clogged and this would cause you to overheat, in this case I would try flushing out the rad or replacing with a new genuine one.
If your other half thinks its the head gasket why not buy one of those kits from a car place like halfrauds and do a sniff test to see if exhaust gases are present in the coolant??
Either way, I wouldn't sell up
just yet. Of course if the deal has already been done I might be wasting my time typing all this, however, if the vehicle ONLY overheats when you are towing im betting clogged rad or water pump. Dont goto a fecking Jeep whatever you do, they are just piles o' ****e
-Wills