Debuted in the 1996 Audi A4, the 1.8T engine became the go-to for high power with good economy. Volkswagen used the engine extensively throughout their fleet. Performance enthusiasts liked it for the extra power that could be urged out of it for cheap. The downside was the long list of heat related repairs that often started before the car reached 100K. In fact, most of the issues with this 1.8T engine are heat related. The turbocharger runs literally red hot under load, and the engine compartment temperatures are way past all the other engine applications. Certain models can even boil their battery dry if the insulating cover goes missing. Only 1.8T cars really need their bellypans, as the bellypan helps control the airflow through the engine compartment.
The 1.8T turbochargers either died for lack of oil changes, or for the grit that built up inside the engines from poor fuel quality and lack of oil changes. High load and speed, and higher ambient temperature usage made the problem more prevalent. Many 1.8T engines of this era clogged their oil pump screens with the same grit, and lost oil pressure and died. Often the turbochargers would get severely worn during the oil pressure loss. The very first models of the Audi A4 and VW Passat did not have heat shields between the exhaust manifold and the oil feed pipe for the turbo. Grit would form inside the pipe and starve the turbo for oil.
Heat hates plastic, and vice versa. The plastic breather system on the 1.8T engine generally fails around 100,000 miles. Each motor code has its own set of pipes, valves and hoses. The vacuum check valves slowly turn from Black/grey to Creme/white and develop craters and pits from the disintegrating plastic. Generally severe air leaks occur which eventually cause misfires, and the check engine light comes on. Further driving with misfires for any reason endangers the catalytic converter, in any engine, not just 1.8T’s. Misfires from failing coils or spark plugs are sure to cause cat failure if unattended.
The valve cover gasket leaks early and hard. So does the cam chain tensioner gasket at the back of the head. Said tensioner has a oil pressure fed piston, and the oil supply goes through the gasket. When it rains it pours. And it pours onto the plastic coolant flange located below it, causing it to warp and fail as well. Certain engine codes correspond to the coolant flange job taking hours. Do not be surprised if you need to replace your breather system at the same time, because some of those parts need to be removed for the flange job, and the breather parts may crumble.
As these 1.8T engines get older, more and more are failing smog. A common reason is failure of the secondary air injection system, or SAI. Most of time we find just a broken vacuum hose or a blown fuse. Sometimes on the 1.8T engines, we find the combi valves are frozen or leak due to the high heat lifestyle of the engine compartment.
Timing belts fail early on a 1.8T engine. Period. And at OMG miles as well. The factory wisdom was that these timing belts would go 105,000 miles. Karmakanik said 75,000 miles, because the belts were just as skinny as the earlier motors, drove 20 valves instead of 8, and were exposed to Hades level heat soaks. So many belts failed early that the factory took back their recommendation and changed to 75,000 and 5 years. But years after the warranties were up. And they would give you a free inspection. But they would not cover the engines that had already crashed.
Do not be discouraged about your 1.8T engine. This page is to let you know ahead of time that certain repairs will be necessary, and that certain measures need to be understood and taken to prevent long term catastrophic failures. Welcome to the world of maintenance. Ask your Service Advisor for some good advice.