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gomi_otaku, VW Technician
Category: VW
Satisfied Customers: 3462
Experience:  VW FastTrack '00-'01, VW Academy Chicago and Seattle '00-present, VW Certified
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2000 Jetta: warning light..started flashing..reserve tank..drove

Customer Question

2000 Jetta, temp warning light beeped then started flashing, pulled over, no steam coming from reserve tank, loosen top slow, as the top loosend steam came out and anti freeze bubbled. Let car cool down, temp when back to normal, got about 5 miles down the road and it did it again this time when I checked the reserve it was empty and nothing on the ground. Let car cool refilled the reserve temp was normal drove about 5 miles, temp stated flasing and beeping again.
Submitted: 8 years ago.
Category: VW
Expert:  gomi_otaku replied 8 years ago.
There's a good chance you have a bad coolant pump. it's typical for the impeller to crack and slip on the shaft.
Open your coolant tank, and pull off the small overflow hose and point it into the bottle (best to have a helper with this, one at the engine and one in the car)
Start it up, and rev up to 2000RPM. There should be constant flow all the time, and should increase smoothly with RPM increase, without spitting/bubbling or a lot of air turbulence. If you have no flow, or it cuts out when accelerated, your pump is broken.
If coolant is not being pumped, it won't warm up the temp sensor- and certainly won't activate the fans, as hot coolant will never get to the fan temp sensor for a long time!