Thanks David for the support! Much appreciated. While there isn't a throttle, Air Flow is most certainly an adjustable quantity. Anyone who has access to a Vag-Com can certainly see this move up and down. The hotter the engine, it is likely that a "leaner" mixture can be made. That may be a pretty cool graph, actually - injection quantity and airflow vs temp. I think I might try getting some samples this summer and this winter and see what happens. I'll post it in a few months (assuming I remember!)
Don't get me wrong here. I do certainly respect Drivbiwire's thoughts. Newbie "hazing", right? He has made some very valuable insights and comments on many of these posts. But, there is not a need to be terse about this stuff. We're all here for the same thing - to tweak out these machines to performance that only folks like us can get geeked out about!
Back to my Beetle running in the 70's... I agree it is either a bad thermostat, or it was the 71C one that was put on in the factory. I'm going to make a change to the 87C to start here and see how it goes. I was going to go with the 92, but I was thinking that it may start causing the fan to turn on. The fan turns on at 102 and turns off at 95. With a 92, that is getting too close for me. With an 87, I think I'll be pretty safe to keep that off more often than not.
I made a few calls this morning. Here are the part numbers, if anyone is interested:
87C Thermostat: 044-121-113
92C Thermostat: 078-121-113
If everyone doesn't mind here, I'm going to do a mash-up. Let's take these quotes together...
Quote by ExtremeTDI
2000 Jetta Tdi gets better fuel ecomomy on the hotter days.
Quote by Ronbros
I agree with tnp, I think we can run much higher temps in the cooling jackets, but finding a thermostat that opens at around 150-160C i cannot find ,am considering making one adjustable. NOW, before anyone shouts, coolant will be a nonwater based coolant
Quote by DrivBiWire
In respect to coolant temperatures, Hotter is not always better. having seen first hand desert testing with VW, Audi, Mercedes, Skoda and BMW they verify every possible operating temperature in order to validate the predicted operating ranges in real world conditions.
Mashing these all together... These engines do run better when it is warmer, as ExtremeTDI says. There is always a point where it is "too hot", as DrivBiWire says. But, I also agree with Ronbros, that we gotta think about pushing the limit up here and testing it out.
If anyone has access to the fuel maps, we can predict if fuel efficiency will be greater with increasing temperature, and we can also see where "the knee of the curve" is, where it starts getting too hot.
Then, we'd need a hotter thermostat, different fan settings, probably a different coolant ratio (I don't think a different coolant), and then some real world testing.
Well, that's my 2 cents... Or, maybe closer to a dime with all this typing! Cool - I blew almost 15 min here at work and I'm sure it sounds like I'm working hard to the boss...