Kevin Phillips

Sorry for yet another coolant trouble post, I've spent the last 3 hours reading every thread about overheating issues,

Here's my situition.
1. 2 weeks ago car started to overheat while getting on the freeway(was an uphill entrance) after some browsing on different threads I assumed it was the waterpump, replaced that and after some purging of the coolant system it was good.
2. Couple days later I make 200ish round trip everything goes smoothly,
3. After a week of sitting I jump on the freeway and its started overheating again,

1. Upper and lower radiator hoses are hot,
2. There's no visible Coolant in coolant; nor coolant in the oil,
3. I get tiny amounts of heat when I first turn on the heater then quickly goes cold(I already know heater core is clogged) it's been like that for over a year.
4. There's no smoke from exhaust when idling

Here's where things get interesting.
1. I assumed it was the thermostat but from my understanding the Lower radiator hose would be cold if the thermostat was stuck closed.

Edit: I tried to purge the coolant system,
Ran the engine for 20-30min with coolant tank cap off,
And every time the fan kicked on the system would bubble over and release tons of air bubbles, then once fan turned off it would stop,

It seems that it's the waterpump but I replaced it with metal impeller less than a month ago, it was ecs waterpump.

Any idea on what it could be, since the fans turn on, and doesn't overheat when idling.

lyleswk

If you run it for 20 or 30 minutes with the cap on, does it ever boil over?

Kevin Phillips

I don't know if this correlates but it only boiled over when the fan kicked on,
Meaning I ran the car with the cap off for over 20 minutes and multi able times the fans kicked on and it boiled over, once fans shut off it stopped boiling over.

Any suggestions on what it could be?

If I had to gues my coolant to water ratio is 25/75 or 30/70
Meaning I only have 25% coolant in there the rest is water.

Kevin Phillips

To answer your question, not that I'm aware of, boiling over would include dumping coolant the the coolant tank, and it's never done that with cap on

lyleswk

The mixture amount shouldn't make a difference. I would run it with the fan on and see if it does the same, i.e. boil over. The system is intended to run under pressure. You may have something as simple as a leaky cap...

Edit: would follow the other thread just now going active on coolant.

lyleswk

Found this musing through AZ forum...

Thermostat test?

the_duke

Is the car actually overheating or is it a sensor issue?

Prospeeder

We are talking about 1.8T right? These cars are getting old enough now that radiators do plug up inside and cause them to run hot. Also alot of debris, leaves ect can build up between the radiator and a/c condensor and kill airflow. You could try the thermostat. They can fail and just not open 100% and then restrict coolant flow.