First thing i'd do is test both the old and the new 'stat with a saucepan of water, thermometer and stove... based on the running temps you've had i'd bet the old one begins to open a bit early and the new one maybe starts to open a bit later than 87°C. Or it could be variations between the old and new temp sensor etc
Being pedantic bang on 80° is running a nats cool, a needles width (or 2) above 80 is where pretty much every 123 and 124 usually runs most of the time IME and while 95 - 100° is a bit hotter than usual (at this time of year at least) it's not close to overheating. Especially if it never climbs over 100
If you do end up replacing the rad for whatever reason there's nothing wrong with Nissens... they're good quality, usually fantastic value for money and when i fitted one to mine a few years back fitted perfectly. There are plenty of places about that can a supply a Behr rad for barely any more £££ but they ain't the same as the origional, it's Behr-Hella these days and the cheaper/aftermarket examples are made in China (Nissens are made in Denmark). OEM Behr from the stealer (assuming that's still what they supply) are a LOT more £££ and while the origional rad is cosmetically better finished than a Nissens it won't work any 'better' for example the copper reinforcing rings in the inlets/outlets of origional Behr rads is a crap way of doing things compared to Nissens take of using a thicker wall plastic that smoothly tapers out.
Duo valve working OK, full cold gives me cold air but slightly hotter setting gives me some really hot air and higher still gets even hotter.
No leaks anywhere no coolant level drops no boiling over. Only key and glove box interior get hot.
Heater temp thing sounds more like a problem either with the control panel or the little air sampling fan that's hidden in the dash (near the glovebox IIRC?) and is fed from the grille in the interior light
Unless the temp wheels are 'clicked' to full cold or full hot the heater should automatically vary it's output to attain the target temp set i.e. i haven't changed the temp setting in mine for eons, in the summer/when the interior is hot you get cool air and when the interior is freezing cold it should chuck out hot air initially and gradually taper the heat off to the set temp as the interior warms up
A hot key and glove box has me stumped
I did wonder if a thermostat that was taking too long to fully open could cause this? Can it behave relatively normal for the first portion of its travel and then slow down due to a fault at the upper temp ranges?
I noticed yesterday the temp ran to the 100c line I didn't do anything and it dropped by it self, but I couldn't hear the fan roaring (I couldn't get out and check).. Might try and see on way home from work today if I can pull over and check fan.
Yeah a stat could behave like that i suppose but i'd think it'd be fairly rare? They don't necessarily fully open much of the time anyway... they should start to open at the temp stamped on them and won't reach fully open for another 15 - 20° (or 102° according to WIS). When there's good airflow through the rad and the waterpump is working properly etc it's the 'stat that's mostly responsible for maintaining a stable running temp... coolant gets hotter it opens a bit more and diverts more through the rad/less back around the engine, coolant temp drops a bit and it closes a little sending less through the rad etc
When you're stationary there's little to no airflow across the rad so it's less efficient and shunting more coolant through it isn't necessarily enough to stop temps climbing hence having fans cut in when the coolant gets hot enough
You don't want the fans to cut in too soon because that doesn't help rad effiency either... temp drop across a radiator isn't as much as common sense would suggest because the closer the rad gets to ambient temp the less well it works i.e. want to run the rad as hot as practical because the larger temp difference between it and the surrounding air the better it works.
After i'd checked the opening temp ranges of the new & old 'stats i'd go back to the fan... 100° isn't quite hot enough to confirm it's dead but with the engine switched off it should be stiffer to turn than when the engine is cool. Carrot (or whatever) tests won't achieve much unless it's hot enough to properly engage and the noise from the amount of air they shift gives that away
