vtraudt

Bought car (120k miles, CAE engine), was in limp mode (underboost). Long test drive ok (aside from limp mode).
At home, cleared code, initially driving fine (good power). Then overheating onf irst real test drive. Verified with VAGcom (coolant temp in engine and instrument module, can hear boiling water in heater core when inside, hot heater core hoses).
Overheats after some idling and/or with slighly elevated rpm (2000-3000 rpm), and quickly on short drives.

Found lower radiator hose COLD.

To rule out head gasket/crack/etc, tested for combustion gas in coolant (my tests were negative).

Determined stuck closed thermostat.

Ordered new aftermarket coolant pump with thermostat.

Installed.

Overheating (no change).

Assume bad cheap thermostat stuck closed. Bought new OEM thermostat.

Installed.

Overheating (no change).

Removed new pump, installed OLD OEM pump WITHOUT THERMOSTAT.

Installed.

Overheating (no change), lower radiator hose (and radiator) cold, heater hoses hot, steam coming out of coolant tank, electric afterrun coolant pump running (plug out, plug in, feels running).


I am at the end of my wisdom:

ANY IDEAS?
ANY SUGGESTIONS?

Bob Petruska

Just guessing, air pocket in coolant system. Audi dealers remove the coolant by vacuum and then replace the coolant while the system is under vacuum. This eliminates any air pockets. It’s a known fact that It is hard to remove air in the cooling system with Audi engines.

vtraudt

Air bubble would explain overheating.
But would it prevent coolant from coming out of the block?

Bob Petruska

Well if the air bubble was near the water pump, then it couldn't pump the coolant through the block.

It would be odd that your block is that blocked. Bottom radiator hose should be much colder than top radiator hose. Coolant exists the block through the upper hose into the radiator,

Is this a Q5 (not shown in you vehicle list), what year, what engine?

Norskie

If you're positive that you've got all the air out, is there a way to disconnect the block's coolant input and output hoses and flush it with a garden hose to see if it passes through? That will at least show whether there's block blockage.

What spins the water pump? Maybe it's not spinning.

Bob Petruska

It's not very easy to remove the radiator hoses............

vtraudt

Compression test: 155-160 psi.