KnifeySpoony

I and some others have changed out the top (super rigid hard rubber) rad hose for the much more flexible silicone hose from the 620R, which is available from Caterham parts. You just need a coupler, very easy install. Too soon to report on effectiveness but no issues yet on my second rad. And btw, your can get a new water rad alone from Caterham parts (ie without oil cooler) if desired.

I have a "race" nosecone which allows more airflow to the oil cooler, although i block the lower opening on cool mornings. I suppose it could still cool more than the standard nose though. Blocking it bumps temps up about 5C on the freeway vs having it open. The highest I've ever seen on track is about 83C.

I can tell you that on my 420R driving to the track on cool fall mornings (in California) - steady state on freeway at 70mph, I'm seeing as low as 41C in the tank. Yep.

The delta between oil temp in tank vs sump will change a lot actually. It will certainly vary with the delta between oil temp in the cooler vs ambient temp, as well as airflow.

Apparently de-aerated oil is easier to measure the temperature of accurately which is one reason that most dry-sump systems have the temp probe near the bottom of the oil tank. It would be nice to have another sensor in the sump to see the oil at its hottest I suppose.

There's already a bung on your dry sump tank ready to accept a temp sender. On my 420R I got a dual temp gauge (oil/water). It came with senders for both oil and water. Just put one into the dry sump tank, and the other replaced the the sender in the "submarine" for water temp. Very simple install. The oil in the tank is the coldest in the system, as the cooler is before the tank, and the oil cools further within the tank, so be ready for some scary low oil temps...

I have a newer 420R and I use the same method as you and get about 6.4L out during a change. Just for another data point. But I'm not sure if my sump design is any different.

I mean, a second+ is a lot when you are at a plateau and chasing tenths. Depends what your goals are.

ZZR about a second quicker in my experience. In terms of durability, the ZZR surprisingly don't seem to wear much quicker. The ZZS developed "chunking" on the edge of tread blocks up front, while the ZZR are not at all so the ZZR holding up better up front actually. ZZS is definitely no slouch on track though, I was surprised how well it performed.

Re: Top radiator hose - I followed in the footsteps of a member here and fitted the top hose from a 620R to my 420R. It replaces just the forward section of the standard stiff hose - I just got a coupler and swapped it in. It's been working well so far. My first rad started leaking after less than 3k miles. I didn't have any bleeding issues and the flexibility of the hose lets me take out my oil catch bottle to empty it instead of having to suction it out.

I mean on current model cars. I think all the superlight series cars came with watts.

AFAIK only the 420R race cars and the 620R come with watts linkage. Maybe the new 420cup does too. My 420R has watts linkage installed from new so I've never experienced the radius arms. Car seems plennnnty lively for me with the watts on - wouldn't want it anymore so.

I have found burping my 420R very simple and quick. Basically just fill into the header tank with the bleed screw open with the car running and the front elevated slightly on stands. Once the coolant comes blasting out of the bleed hole, it's done.

Interesting, I never would have guessed. Is it easy to tell by looking? would it automatically require replacement?

I just a bubble level on the bridge and it is level/parallel with the lower front horizontal chassis tube. So it seems it's not actually bent. Maybe control arm chassis mount? I really wish something simple just broke, then I could replace and move on. It being a mystery is unpleasant...