Thermostat replacement?


Veteran Member
Nov 26, 2002
CT TDI Corral
'03 GLS 5spd
My search turned up no dedicated thread to this subject.

Had a problem with the warm/cold cable coming loose (the lever the cable operates dropped down and disengaged from its whatchamacallit) which I fixed and everything seems hooked up properly except there is very little if any heat being made. Also this summer, the AC was suspect is a thermostat issue -- there is no code thrown but this is my best guess.

Anyone have insight/experience this one before? A part number or approx. cost? Alternate theories wth is dogging me here?

Thx in advance for your inputs.

JJ -- 2003 Jetta


Top Post Dawg
Jun 27, 2001
underneath something
2001 Golf GLS TDI Reflex silver, rough road suspension and steel skid plate, 2004 Passat Variant, Candy White, rough road suspension and geared balanced shaft module, and much, much more. 2016 LR RR HSE TD6, 2019 Jaguar I-PACE
How's the air flow through the vents? Strong or weak? If weak you've got something blocking the air from passing through.

When was the last time the cabin air filter was replaced?

Got VCDS? What temperature is reported by the ECM? What temperature is reported by the instrument cluster?

Powder Hound

Top Post Dawg
Oct 25, 1999
Under a Bridge, Crestview, FL, USA
'00 Golf 4dr White 5sp, '02 Jettachero 5sp, Wife's '03 NB Platinum Gray auto(!)
First, what MOGolf said.

After that, if the engine temp never gets up out of the lower left hash marks, you either have a failed coolant temp sensor or a failed thermostat.

If the engine coolant warms up, then you will have heat in the cabin, unless there is something blocking airflow like MO suggested.

If the thermostat has failed, then the engine may never warm up enough to provide sufficient heat to unfog the windsheild.

If the a/c barely blows, then you're back to checking the vents and fan like MO said.