Auxiliary Water Pump replacement query

[dieseloz]

Symptom: Warning light on dash, error code 09754 : Coolant Pump 2 Open Circuit P261A
Vehicle: 2009 Golf Mk6 VI TDI

The chief fix, for 75,000 people who have had this error, is a new coolant pump 2, also known as water pump b, or additional water pump, or an auxiliary water pump, or an afterrun water pump, or a heater pump

A typical replacement is Part # 5N0965561A that runs $530 from VAG Australia (Pierburg or Buehler) with another $126 labour and $132 for G13 coolant. So nearly $800 to replace through a stealership.

Alternatively, get a $70 cheapie like the BAPMIC on eBay (risky, error code may not clear, or part may fail prematurely).

Here's one bloke doing it himself:

Question:

1. I am planning to buy a new vehicle within the next year to 18 months, so I would rather not get involved in replacing this pump, and onsell the car "as is" to the next owner.
2. I believe this pump is used to circulate hot coolant to the heater when the engine is off, but I never use the heater (it's hot in QLD).
3. It may also be used (unconfirmed) to cool the engine after the engine is switched off, which can be circumvented by allowing the vehicle to idle for a few minutes before switching off, when the engine is very hot. (I saw a comment, probably not relevant for diesels: For V6 engines, I know the electric water pump will do its job when you turn the car off to prevent cylinder head warping due to overheating. )
4. I've seen some comments that this pump may be used (unconfirmed) to keep the EGR (exhaust gas recirculation) unit cool. Someone commented that if this pump is not working, the ECU keeps the valve to the EGR unit closed, which means your exhaust has more Nox gases, but I'm not aware of any damage to the vehicle.

So why should I not simply leave this error code and continue driving for another 12-18 months?

Thanks for any comments!

 

[dieseloz]

Updates:

My local VAG dealer says:

The additional coolant pump is to keep the correct flow rate required throughout the system if more is required.
I believe this one helps the flow to the coolant flange, egr cooler and firewall.

This page says it's even more complex:

1. To provide back-up for the mechanically driven coolant pump at low engine speeds and to ensure adequate coolant circulation. Switching levels: Cut-in: < 840 rpm and > 108 °C Cut-out: > 3000 rpm or < 106 °C
2. To circulate the coolant during continued coolant circulation
3. The activation condition and continued coolant circulation period are constantly calculated from the time of starting the engine. For continued coolant circulation, the pump and radiator fan are actuated in parallel. The maximum continued coolant circulation time is limited to 10 minutes. Examples of activation condition as a function of ambient and coolant temperature:
   Ambient temperature 10 °C, Coolant temperature 110 °C
   Ambient temperature -10 °C, Coolant temperature 115 °C

Interesting comment from an Audi forum:

I used to be a staunch supporter of aux pump but after years of running without one (I was forced to remove it due to RS4 intake manifold with enlarged plenum which left no room for the pump) I can decisively say that one is not needed at all. It was added to the design to prevent coolant boiling after shutdown at the trigger point from factory is 108C. Healthy car should not exceed ~95C in the heat of 95F summer. It only kicks in if the temperature threshold is exceeded at time of shutdown, not some time afterwards. The result is that in factory mode that never kicks in...and if it does you better investigate your cooling system as it is definitely running WAY TOO HOT to begin with.

Simply not shutting down immediately after going WOT [note: wide open throttle] is all you need to have zero issues with turbos. Due to the fact that our turbos are coolant cooled and oil cooled, they cool down super quick. The cool down period (idle for few minutes) is only really applicable to oil cooled turbos (they get no coolant) and especially BB type of such turbo since the amount of oil flowing through the turbo is very small.

So, deleting it is fine.

Other comments point out that if you allow the engine to idle for a minute before turning off, the turbo quickly reduces the engine temps to normal. Another technique to prevent overheating and do without the aux pump is to roll down windows and run interior heaters on full to pull heat from the coolant.

 

[dieseloz]

No replies. I won't replace this plastic junk pump.

Saw this on YouTube

okay Mark Fagan says: "what do you think of a volkswagen?"

Well Volkswagen they make lots of cars they have I could go through days of histories and analysis how old Adolf came up with the idea the Volkswagen took millions of deutsche marks from the Germans and never made a single one, spent it to make bombs and tanks and stuff instead, up into modern day where they're extremely high-tech company that don't Porsche Audi they own all kinds of companies and they're getting into electric cars now but in the united states I would not buy a Volkswagen, their parts are expensive, they're very hard cars to figure out, if you're a private individual you go to the dealer they always screw over their clientele, they charge them too much money to fix them, and the parts are super expensive, now in Europe they're very popular, people know how to fix them, the parts are cheaper, it's another ball game, but in the united states they've already found out they're having a real big problem. In Germany I believe something like percent of the electric cars sold this year were Volkswagen electric cars not so in the united states, hardly anybody's buying them, they have a bad taste of the bad Volkswagen dealers, overpriced repairs, expensive costs, so they got to get rid of that bad image, that's going to take a while to do, but their regular gasoline cars I'm not a fan because they're too high tech and they break down too much, they cost too much money, and then when you want to sell them they have no resale value, so not a fan of American Volkswagens.

He says the same about BMW: