My 2001 TT roadster is overheating. Shortly after starting the car it pegs the needle to hot and the warning light comes on.

I replaced the water pump, thermostat, coolant temp sensor, coolant reservoir, fan control, backflushed the cooling system and filled it with G12 and distilled water.

The system has been burped numerous times and the coolant level is constant.

There is no steam or sweet smell from the exhaust, no coolant in the oil or oil in the coolant.

I'm at a loss, does anyone have any ideas???

 

Is it actually overheating or is the gauge just saying it is? Are the radiator fans coming on at all? Very interesting.

 

It gets up to 124C and the fans are working.

I did a pressure test on the cooling system and it holds 15 psi.

 

ooooh.. That's way too hot. If it's gotten that hot too many times, it's probably damaged the head or head gasket. I know you've pressure tested and are not getting any antifreeze smell from the exhaust but it's possible that there is a small crack in the head between the exhaust ports and the water jacket in the head. It also could be a little bit of ignition gases slipping by the head gasket directly into the waterjacket. It doesn't take but just a little bit to heat that water up as hot as the exhaust gases are inside the head.. You may have to pull the head and have it checked for cracks and straightness at the block mating surface. While the system may hold 15psi during the test while cold, it may be failing at the much higher psi's that accompany combustion inside the cylinder and when things get up to operating temp. Those pressures are much higher and can prevent water from entering the exhaust cycle therefore preventing you from detecting it at the tail pipe. Either way, overheating an aluminum engine several times almost always warps or cracks the head in some way.