Some views from a guy who services them regularly:
1: there are several "1.8t" engines, and they cover two VERY different engine families, EA827 (early) and EA113 (late). Like the difference between an AHU and an ALH, respectively. Passats from 1998 through early 2001 will have the early type, 2001.5 to 2005 wil have the later type. Audi A4s got the newer type a year or so before the Passat. All Golf, Jetta, NB, TT use the later type. There are about 7 different 1.8t engine codes, too. They cover 150, 170, 180, and even 225hp versions.
2: the versions found in Passats (and their stablemate, the Audi A4) are NOTORIOUS for sludging problems, primarily due to their smaller oil capacity because of the shape of the oil pan that must hump over the subframe. The TSB that stated to use the larger spin-on filter, like the older diesels use, helped that somewhat.... but they still do not hold as much oil as the G/J/NB/TT.
3: they use some oil, and this, if not kept in check, also makes for sludging issues if people do not keep the oil topped up.
4: they need 505.02 spec 5w40 oil. This requirement was also listed in the TSB, since lots of places were just putting any old synthetic (usually 5w30) or worse, just bulk 5w30 rando-lube oil, and possibly a crappy filter.
5: they have a timing chain. Volkswagen CANNOT make chains that last, period. If the chain itself does not stretch out and start flapping about because the tensioner show wore out, its the electrical part of the cam phaser (all later 1.8t engines have variable intake cams) that fails. These are expensive parts, and a pretty big job to replace.
6: early ones had timing belt issues, that were remedied with a new style belt and tensioner, and they are NOT compatible with the old stuff. Lots of people would put a new style belt on an older engine with an older tensioner, and they would not run right. Gotta replace it all together.
7: plastic water pump impellers are about thrice as likely to break on these than on TDIs, presumably because the engines spin faster.
8: the breather system, the vacuum system, and the turbo control system are probably one of the most complex, over engineered messes of molded rubber hoses, check valves, and plastic bits you will ever see in your life. I've spent MANY hours chasing down intake/charge air leaks. The AWM engine in the 2001.5+ Passat has no less than FOURTEEN one-way check valves, and they are so common to rot away and cause all sorts of problems I keep about 10 of them on the shelf here.
9: most 1.8t applications have secondary air injection, which is an emission control system specifically designed to get the catalyst up to temp and provide endless income for automotive technicians. How a system that only need work for about 30 seconds after a cold start can cause so much trouble is beyond me, but whatever, I did not design it. Simple enough system, but they ALWAYS are breaking, and parts are expensive.
10: manual transmission 1.8t cars use DMFs, and they fail even more than they do on TDIs. Through 2000 Passats' ZF autobox has a design flaw in the valve body that causes some trans problems. Other 1.8t engines got bolted to 01Ms (yes, you can laugh, I did).
11: most 1.8t engines have an electric vacuum pump, to assist the brakes. These are located in a lame spot down low on the G/J/NB/TT, exposed to the weather, and can fail, and are very expensive. Passats and A4s not so bad, as the pump is located up in the engine compartment next to the PS reservoir.
12: all the later 1.8t engines eat coil packs. They eat them like a fat guy eats candy. VW keeps recalling them, they keep redesigning them, they keep eating them. I *think* the latest versions, which have only been around for a few months now, may be better.
13: the 1.8t engines, like all modern VAG gas engines, often have catalyst failures, as well as lambda sensors and MAF sensors. They are VERY finicky about fuel control, and do not tolerate much of anything out of whack.
14: they require premium fuel. If you use regular, not only will you have slightly reduced power and poorer fuel economy (because they ECU will pull timing from the knock sensor input), but you will also run the risk of cooking the turbocharger, as EGTs go up when timing is retarded. So you may save a whole 75 cents when you fill up, but you will spend $1200 every 50k miles replacing the turbocharger.
