I think the high underhood temps have manifested themselves by the fact that every motor mount, every hose, all of the coil packs, the alternator-virtually ANYTHING even remotely heat sensitive plastic or rubber has been replaced on this car at 100k or under.

As for the airflow through the radiator, I was wondering about that, but I really don't see much area for the air to exit the engine compartment (providing a low pressure area) w/ the cover in place. There are a couple of very small louvers at the rear of it, but otherwise not much. Maybe around the axles? Of course, this hot air exit could explain why both inner CV joint boots were shot (I just replaced both axles at 103k-one boot was totally shot, the other cracked); typically it's the outer boots in my experience that go first due to the flex with steering (when I lived in Alaska, if you left the wheels turned in your Subaru at 30 below when you parked, you could plan on tearing a boot almost instantaneously when you drove away).

We'll see. I have never seen a car (other than a Range Rover) that piled up $16,000+ in underhood repair receipts in under 100,000mi as this S60 did (my nephew, the previous owner). They loved the car, but between the $28k in depreciation, the repair bills (I didn't mention 3 cracked and bent 17" wheels from Dallas road potholes), the expensive tires ($300 ea from dealer every 30k), they just could no longer justify the expense.

I can't say heat contributed, but anytime I opened the hood during their ownership it seemed incredible, but life's an experiment.

As for synthetic, the first 50k they had Volvo use "Volvo" branded synthetic (I don't know who made it for Volvo), and since then it's been Valvoline I believe. They paid $60-$75 per oil change, so I'd like to think they got the better stuff.

I use diesel oil in my other vehicles that have flat tappets (I have two diesel among my 8 cars), but I think I will use the few cases of Amsoil 10-30 synthetic I have left over from a twin-turbo Nissan I once had in the S60.

I used WalMart supposedly "full" synthetic in my 965 and the valve cover stayed like new the entire time I owned it. The 5cyl S60 (basically same engine, of course) looks like peanut butter in there, and I am waiting for something to clog an oil passage, so a VERY slow cleanout would be safer.