My 2000 2.0L Golf GLS won't blow hot air at operating temperature, the air is only lukewarm at best. This started a few months ago inexplicably. The car isn't overheating or underheating, it reaches operating temperature in the same amount of time as before. Here's what I've done:
- Checked coolant level - there's plenty.
- Flushed coolant system - the previous owner mentioned this same problem and a flush solved it for him, no such luck for me. Ran some Prestone Flush, then flushed water twice, then refilled with regular Prestone (not G12, I know). The only thing that worries me here is that I never felt like I was able to drain all of the fluid when flushing (always found: amount in > amount out).
- Bled coolant system - elevated the passenger side (where the bottle is) by driving up onto a snow bank, let it run for 3 minutes. Coolant level didn't change.
- Tested thermostat - works correctly and opens right about 195 F. Note that on this vehicle the thermostat blocks off the radiator loop, not the heater core loop which is separate and not controlled by a thermostat.
- Checked for heater core blockage - using the input and output connections at the firewall I was able to pass fluid through the core using both gravity and light pressure. Flow rate was substantial, don't suspect blockage.
- Checked water pump flow rate - using a clear hose I bypassed the heater core altogether and ran coolant from the engine block output straight back to the coolant bottle. At idle the pump wasn't able to overcome gravity to push up and into the bottle, but as soon as the engine rev'd coolant pumped quickly and with ease.
- Checked water pump - OEM VW pumps use a plastic impeller and I suspected it had broken. Pulled the pump and found it was already the metal impeller kind; turns out the previous owner replaced it 2 years ago. Put the old one back in, it's still good.
My car doesn't have Climatronic, just the standard climate control system; does that mean it's cable or vacuum controlled? At this point I'm wondering if there isn't simply a fan control gate that's stuck or something. Even though I was able to pass water through it, are there any gates or controls within the heater core itself?
Replacing the heater core is a 8-16 hour DIY job or $850 down at the shop, and I'm not prepared to do either. Short of actually looking at the core, is there anything else I can try, check, or do?
Thanks all, I've been wracking my brain with this one and would love input!
After trying my best not to I decided to replace the core. I used a very helpful VWVortex guide along with a Chilton's manual. 14 hours later I've got air that measures significantly hotter than before, so now it's time to wait and see how things go this winter. I found that I don't have a split HVAC box even though I don't have the Climatronic system (major letdown) and that the flappy bits inside the box were in great shape and moved freely. The old heater core was definitely clogged; simply trying to blow air through it was difficult. For your enjoyment here's what the car looked like when I was finally able to remove the core: