Resolved!
having same over heating problem as needle moves towards right @10 on uphill, had a thermostat that started to open at too high a temperature. The first symptom was the cooling fans were always on. Then it started to overheat under load.based on my home work from TDI club and other sites, found thermostat was the culprit. thermostat sticking, opening late.
symptoms/solution:
1) problem started in last week of February right after i had 1k mile round trip. never had this before. during trip it was driven 70 ~ 85mph for minimum 4.5 hours without stop.
2) when ever driven under load specially in 6th gear, even on light uphill between 65 to 75mph. temp needle drifts towards right and slowly comes back in middle. sometimes needle moves back to middle right a way.
3) had around 59k miles on odo and it was due for OC.i had dealer flush the coolant as well, in hope that radiator flush would rectify this overheating issue!. coolant flush reduced some what of needle movement. but was not enough for me to say resolved!
4)one thing i noticed! from last week in February, right after driven to operating temp, when ever it was parked , fan always kicks on after 1 second of ignition turned off,without missing a single day!. and i know it was not in regen.
5)to rule out other possibilities like head gasket ,WP. to rule out head gasket did hydro carbon test came out negative. WP was working fine since never missed slightest heat in cabin as well as did check reservoir hose that connects on top coolant reservoir,it had steady flow. upper radiator hose from engine to radiator felt pressurized and it was getting very hot to touch, the way it supposed to be.
6)one thing during this ordeal "bottom radiator hose that connects to thermostat housing never felt warm" or for sake Luke warm. it was always remained cold or enough for me to say dead cold. last checked @ dealer after 1.5 hr drive while ambient temp ~ 90F. "cold".
7) t-stat housing ordered thru dealer, made an appointment to change thermostat. in CKRA passat it's whole thermostat housing, dealer ask, if i want them to diagnose overheating instead of me telling them to go ahead and replace thermostat, as they have been aware of it since my last visit for OC & coolant flush. but according to dealer from last visit, as long as needle does not move to red zone it;s not considered overheating. second thing is for dealer to duplicate this, they need to drive under load on hilly area, which is not possible by them and i knew they'll come back stating can't duplicate issue. diesel engines are so heat efficient, even if they leave car running for several hours in their shop temp needle will not move past midpoint.
8)Changed t-stat, drove under load on the same road, needle did not move a bit from 190F. Stayed steadfast @190F. upper rad hose very hot, bottom very warm. while A/C off & engine running Fans are not constantly running (it cycles on/off though) while idling. got relief from daily occurrence of having car parked & rad fans were keep running, after ignition off, not any more!. - problem solved!!
8)for me, the key indicator for bad t-stat was the cold lower radiator hose that connects to t-stat with a hot upper radiator hose (at any given time no matter what ambient temp was!).-thanks