Ahh...the jetta...you don't want to get me started on German engineering...lol
The 1.8T is a gasoline engine, I'm not sure of the displacement on the diesel but the diesels are badged 'TDI'.
Mine is an 02 and it has right at 65K on it (had 59k when I bought it).It's actually a great car when shit isn't breaking, it gets 30mpg regularly and is a comfortable, smooth-riding car. When shit breaks on them it's either really expensive to fix, or a humongous pain in the ass to fix. You have to pull the entire front clip off of the car to get to anything, even the thermostat. One big problem the jettas have is that from the factory the water pumps have plastic impellors, so over time of heating up and cooling down and heating up and cooling down the impellor says 'hey, guess what, I'm goin to disentigrate!'. Mine started overheating about 3 weeks ago (about 2 months after I bought it), and the first thing I noticed was one of the cooling fans wasn't working. I tested the fan motor, found it to be bad, and replaced it (which meant I had to pull the front of the car apart). The car still overheated. I checked the flow coming from the coolant hose, and it flowed ok at idle but off-idle it didn't flow any more than it did at idle. I pulled the front of the car apart AGAIN and removed the timing belt and water pump. Not surprisingly, the impellor was in about 8 little pieces. I went to the dealership and bought a new water pump, timing belt, and thermostat and replaced them which took me about 4 hours of labor (keep in mind that I'm a technician who usually flags 10-15 hours in a 7 hour work day). Got everything back together and the A/C wasn't cooling, and upon further inspection I found that the OTHER cooling fan wasn't kicking on, and the one fan that was working was only coming on low-speed. Both the condensor fan AND the fan control module were inoperable, so I pulled the front of the car off a third time and replaced both the fan control module and the condensor fan. After all that, everything in the cooling/ac system works great. A few days later I noticed a slight misfire when the engine was cold. Since VW's are notorious for having ignition coils take a shit, I replaced all 4 coils and spark plugs. It still occasionally misfires on cold start, but I'm just going to deal with it for the time being. The only other gripe I have is that when it's cold it has a rough 1-2 shift, which I'm pretty sure is caused by a seal in the transmission leaking a bit (since I can duplicate the problem under full-throttle), and I've been meaning to put some conditioner in the tranny to swell the seals but I haven't gotten around to it yet.
But, all in all, I'm very happy with it...however, I don't ever plan on buying another VW unless it has an extended factory warranty.