What It Is
An OEM thermostat made by Mahle Behr, covering Mk3, B4, Mk4, and B5.5 VW TDI models.
Why This Part Matters More Than It Seems
VW thermostats fail often, and a failing one is easy to overlook since your dashboard gauge can still read a normal-looking temperature even when the engine is actually running cooler than it should. The engine burns fuel to generate the heat and pressure that drives the pistons and moves the car down the road. An engine chronically running at a lower actual temperature, even if the gauge shows what looks like 190°F, will burn more fuel than one properly running at its intended operating temperature, all else being equal. A working thermostat is central to good fuel economy for that reason.
When to Replace It
If you can't remember the last time your car got a new thermostat, it's worth checking now, especially if you've noticed reduced fuel economy without an obvious cause.
Fitment
2001-2006 Volkswagen Golf, Jetta, and New Beetle, and 2004-2005 Volkswagen Passat.
Common Questions
How do I know if my thermostat has failed?
A common sign is reduced fuel economy without another clear cause, since the engine may be running cooler than intended even if the dashboard gauge looks normal.
Why does engine temperature affect fuel economy so much?
The engine burns fuel to generate the heat and pressure needed to drive the pistons. Running chronically cooler than the intended operating temperature means burning more fuel to do the same work.
Is this a genuine OEM part?
Yes, made by Mahle Behr, an OEM supplier.
How often should this be replaced?
There's no fixed universal interval, but VW thermostats are known to fail often, so it's worth checking if you can't recall the last replacement.
