The fans shouldn't have any impact on cooling at freeway speeds so that leaves tstat (but would probably show as cooling efficiency code or overheat @idle) poor coolant flow(apparently not with return to overflow) or poor radiator performance from blockage or airflow issue, worst case would be head gasket issue.

Was the impeller broken or cracked at the splines? If it was in bits how much do you think you got out? Aftermarket impeller design could be a problem, but I haven't seen that on a vdub. Last item, you mention the fans work as they should. If it has a mechanical and electric fan, the electric one should never come on unless the AC is on or the temp sensor sees an eminent overheat from a bad mechanical fan or lack of cooling.

I'd lean toward a blocked radiator. How's the heater? I've seen a bunch of Passats with clogged heater cores and a few with clogged radiators. Most of the ones I've seen with issues have a white/grey slime in them that insulates the tubes from transferring heat properly. With that low of mileage and its age, I'd say that mystical @#$%$ that VW put in for coolant finally went south.

Buggsy,
Clogged heater core would not cause overheating definitely, Are you sure vehicle is overheating or we have faulty ECT or IC, VW cooling system is easy to diagnosis, once you remove expansion tank cap (engine operating temp.) if is there is no overheating coolant level is just gonna raise up but will not over flow. Make sure that overflow hose at the tank is not restricted and would be nice if you could monitor the temp with the scan tool while on freway and with the IR temp.gauge while is running prior to overheating if so. good luck.

Bresha

Thanks Turbo,

After working on any cooling system that needs to be refilled, I use the Snap On Air Lift System. It applies vacuum to the system drawing all air out of the system then refills. It's a reliable way to eliminate air pockets during coolant refill on any vehicle.

You probably already know the tool I'm talking about. It's dependable to the point where if used properly, you can be confident that all air has been removed from the system.

The owner also reported that the overheating condition was found only at a sustained 2500 rpm and up and that a turbo gasket was at fault.
I have no idea as to what gasket he's refering to. He may be right, I just don't know.

Buggsy

When asked if the fan could be heard running, or if any steam could be seen, or if he could hear bubbling like a percolator, he answered that he did'nt know because his wife drives the car most of the time. When he did drive it, it was fine in town but when on the freeway the gauge went up
and the stop engine lite came on. He pulled over, let it cool down, exited the freeway, and it was once again just fine. He did not hear the fan, see any steam, or hear the coolant boiling.

I'm not sure if the gauge, the ECT, or the owner is accurate in their description. What I will do is hook up a scantool and have my boss take it for a run on the freeway to confirm an overheating condition or not.

Thanks for all the helpful info.
Buggsy