sTTacey

Ah jeez...my '03 TT was at the dealer for a whoooooole week (50k service $150, fix R turn signal which had residual clicking $300, and repaint hood from a hardwater/chemical stain + rock chips $blahhhh)...got it back all shiny new...4 days later it suddenly overheated whilst driving normally on the hiway...

(1) red coolant temp icon flashed on
(2) temp gauge on H
(3) pulled over to check the coolant level, totally normal (half expected it to be squirting out or something) and engine didn't seem hot at all
(4) got back in the driver's seat: temp normal, no warning light.
(5) 2min back on the road, OVERHEAT again.
(6) hobbled to dealership on a street with many stop-lights (i.e. had to stop or idle every 45sec)...so as soon as it would start creeping back up to H I'd have to stop again and it would go back down. Took about 45sec with the clutch engaged to heat up, and also about 45sec while stopped to cool down.
(6a) at my destination, ejected a cd from the cd-player in the dash and the cd was super hot, weird!

The thermostat is newish so it's likely not that. No solution at the dealership yet. :-( They did say the circuit/fan in the dash passed muster though...cause I asked.

This is an omen...I might show up at TT-West in a Mk2 TT (gray of course), hehe. Not sure I can give up my stick-shift though. Grrrr.

SlapTTy

Could be a bubble in the coolant lines. Did you run it at idle for a spell with the coolant reservoir cap off? That might "burp" the system.

Easiest and cheapest thing I could think of off the top of my head.

sTTacey

Nopers didn't try that...I thought taking the coolant cap off while the car is hot is a nono?

Just now, dealer said they're thinking it might be the water pump, but it'll cost $200 to get in and look. And then $1600 to actually fix the pump. Argh!

AudiMick

You can let the engine cool down then run it with the cap off to burp it. Don't remove the cap with a hot motor.

The plastic impellers do fail on the original water pumps. $200 + $1600 is about twice as expensive as it should be.

I paid $750 for the whole deal about 18 months ago. Call around.

sTTacey

Yeah a coworker also said he had similar work done locally (non-dealership) and it should be half as much. Thanks for the input.

AndymanTT

got my TT a week ago 2003 60K miles - called a mechanic about the timing belt change. Scheduled it for a week out. Water pump beat me to it.. Mechanic said it broke into 3 pieces.

kappa-q

Plastic impellers on stock water pumps do have the nasty habit of disintegrating, which obviously lowers their ability to perform their push water duties, and it introduces all the nice shards of impeller to block things up elsewhere in the system.

A quick check is to open the resevoir cap and look for flow from the return line. That should help you identify if water is getting pushed around, but may not help to ID a partially broken impeller.

Common practice is to check the fuse block on top of the battery as the left most green/30A fuse on the right side of that block is for the fans IIRC, and historically corrodes, and melts things nicely when it's impedence gets high enough.

If you can access the radiator fan switch, you can remove the connector and jump the pins to confirm the fans run IF the switch tells them to. You'd have to put the switch in water to see if it closes at the specific temperature, or get a meter on it to confirm ~0 Ohms/closed state when the coolant in the radiator is toasty toasty.

On the other hand, if everything mechanical is actually working properly, there are two other options: you may just have a green top coolant sensor that is crapping out and sending bad signals to the dash, or you can have a dash that is starting to crap out.

All that said, the fact that you can drive and overheat, and then stop and it will catch up really indicates insufficient flow through the radiator to keep up with the heat generated while driving. And that when you lower the heat generation at idle, it then has time catch up and cool things back down. Most likely you are looking at a bad water pump and it's time for a timing belt job. Anywhere from say $200 in parts if you do your own work, to maybe $800 at an independant shop, to a mild to severe raping if you choose a stealer.

With some of the horror stories out there of shops charging for the work, but only doing some of it, unless you have a trusted shop/mechanic, ask for the used parts back when the job is completed. If they have to come up with used parts when all done, it's more likely they'll actually put all the new/shiney parts into your car first.

SlapTTy

This.

If you end up getting the WP replaced, you may as well do the Timing Belt as well. It shouldn't cost much more than what has been posted here unless my reading comprehension has slipped and you already did that.