Coolant flush on VW GTI MK7 questions

[geyungjen]

Dear All,
The coolant color for my GTI MK7 appears to be brown:

It should have been pink:

I think it's time to flush or replace with VW coolant.


Put the car on the ramp, remove plastic splash guard, I suppose this is coolant hose that needs to be unplugged to drain old coolant?

There is a electric connector on top, shall I unplug it? I see someone on Youtube unplug it, but I do not understand why.

Here is the manual reference, the connector on top is to supply power to the coolant pump (yellow)

My questions:

To drain coolant, simply unclamp the coolant hose from bottom, and disconnect coolant hose after placing catching oil pan to capture the coolant?
Do I need to unplug the electric connector from top? (Engine is off and cold)

Thanks for your inputs

 

[Dr Sheldon]

Do I need to unplug the electric connector from top? (Engine is off and cold)

Makes no difference to the flow of water !!

You will never (easily get all the coolant out from the crevices anyway.


You would do well to use a Coolant System Flush / Cleaner !! Dishwasher tablets or Persil works well for me !!

 

[geyungjen]

Thanks for the reply.

I was also thinking about this:

Use a hand extraction tool, available from hardware store, to suck the coolant out of the reservoir, say a gallon, when the car is off and cold and then fill up the same amount with distilled water, then run the engine until the reservoir shows colored coolant, then turn off the car, wait until cold, repeat the same process several times, each time sucking a gallon.

In the last time, fill the reservoir with new VW coolant.

The downside is there will be part of the liquid to be distilled water, not coolant in the system. By the way, I am in Caliofornia, warmer weather will not freeze the water.

The upside is, no need to disconnect anything, because it may not be easy to disconnect the coolant hose and reconnect tightly.

Is this approach feasible?

Thanks again.

 

[geyungjen]

Thanks for the reply.

I decided to drain from bottom, had to struggle with clamp with a pair of plyers and fight with stubborn rubber coolant hose, I did not use metal tool for fear ripping the rubber hose. It needs good strength.

Finally get the hose off.

I add 2 gallons of distilled water which will displace the coolant in the system and let it keep draining.

At the end, I will add VW premixed coolant.

While it will not complete flush the old coolant, hope this will improve temperatures.

Thanks again.

 

[LeBron]

Oh boy. A few thoughts. First, yes you definitely need to flush that cooling system. Not sure why it is brown, but I will share this. My 08 Passat ended up with some sort of debris in the coolant passages that found its way to the water pump impeller, locked it up, which are every single tooth off of the timing belt in a matter of seconds when I was at high RPM pretending to be a race car driver on the way to work. Upshot... engine went out of time, every piston hit every valve, and here I am today as the proud owner of a personally rebuilt, upgraded engine (the one I killed). Yes, some piece of hard debris in the coolant system got lodged between the pump housing and impeller (metal impeller). Me...I would be flushing really well. Run distilled or other recommended through the engine several times and drain AFTER basically pulling every hose I could off and cleaning etc. Debris I experience was likely piece of metal from aluminum cast head that had corroded and finally let go. That brown color you have is disturbing. I might have it chemically analyzed by a transmission shop or similar for content. Could be rust but could be many things. I don't recall what transmission fluid leaking from oil cooler looks like mixed or even oil.

Also, be sure you know what that connector is. My yellow connectors are for crash impact sensors. Want to be careful with those. Good luck

 

[geyungjen]

Thanks for the info. I will keep an eye on this.

 

[geyungjen]

I have flushed the coolant with 2 gallons of distilled water, then add coolant concentrate designed for VW GTI MK7 (not the premixed one) to arrive to apromixate coolant water ratio. The engine temperature is noticeably improved. Before, the temp meter needle on the dashboard will quickly point to "12 o'clock", now it mostly stayed at "11:55" during driving in a hot day.

 

[Uwe]

the temp meter needle on the dashboard will quickly point to "12 o'clock", now it mostly stayed at "11:55" during driving in a hot day.

Temperature gauges on VWs have been a joke for decades. Check your coolant temp with VCDS.

-Uwe-

 

[Dr Sheldon]

Before, the temp meter needle on the dashboard will quickly point to "12 o'clock", now it mostly stayed at "11:55" during driving in a hot day.

Are you making this up as you go along ?

Temperature gauges on VWs have been a joke for decades. Check your coolant temp with VCDS.

-Uwe-

Since when has Coolant Quality dictated Engine Coolant Temps ??

Surely it is the ECU (looking at ECT and Fan Control) that will dictate this ?

 

[geyungjen]

Are you making this up as you go along ?



Since when has Coolant Quality dictated Engine Coolant Temps ??

Surely it is the ECU (looking at ECT and Fan Control) that will dictate this ?

I have no reason making this up

See the temp meter near the bottom of the dashboard, this was last time before coolant flush in a cool weather, it points to 12 o'clock; after flush, it is like 11:55, although I did not take photos.

I connected a handheld OBD2 device designed for VW/Audi:

Connected this device during road test and read Datastream for all coolant temps and oil temp, saw only one short period coolant temp reached 103 C, most of the time aroung 100 c or 99 c, in a relatively hot weather during noon time on my way to Berger King, in a stop and go traffic.

I suppose temp meter on the dashboard reads from the same data source as the OBD2 device or VCDS does.

Since when has Coolant Quality dictated Engine Coolant Temps ??

Quality of coolant may indirectly affect the coolant temp, because dirty coolant may a). lower the boiling point, boiling point of 60/40 mix would be at 129 c; 50/50 would be around 119c, pure water would be 100c. Vaporization would affect cooling effect. b). Dirty coolant because of particles inside may flow slower than fresher coolant, slower coolant circularization may result in higher coolant temperature as it takes longer time to reach the radiator/fan where it is cooled down before flowing back to the engine.

Then I asked AI:
dirty coolant same cooling effect?


AI Overview

No, dirty coolant will not have the same cooling effect as clean coolant; when coolant becomes dirty, it can significantly reduce its ability to transfer heat effectively, potentially leading to engine overheating due to restricted fluid flow and reduced cooling efficiency.

 

[Dr Sheldon]

I suppose temp meter on the dashboard reads from the same data source as the OBD2 device or VCDS does.

It does but the Gauge on the Cluster (not just VAG) is programmed the keep the driver happy not to give an Accurate reading.

No, dirty coolant will not have the same cooling effect as clean coolant; when coolant becomes dirty, it can significantly reduce its ability to transfer heat effectively, potentially leading to engine overheating due to restricted fluid flow and reduced cooling efficiency.

And the ECU will continue switching the fans at the same temperature

All it will do is look at ECT and fans on and off at the temperatures it is programmed to do so.

No, dirty coolant will not have the same cooling effect as clean coolant;

I am not discussing the Cooling effects of different liquids !!

Quality of coolant may indirectly affect the coolant temp, because dirty coolant may a). lower the boiling point, boiling point of 60/40 mix would be at 129 c; 50/50 would be around 119c, pure water would be 100c. Vaporization would affect cooling effect. b). Dirty coolant because of particles inside may flow slower than fresher coolant, slower coolant circularization may result in higher coolant temperature as it takes longer time to reach the radiator/fan where it is cooled down before flowing back to the engine.

That may wash in an old school car with the fan on a belt, possibly a viscous where the coupling is not communicating with the ECT sensor.

That theory holds no water (pardon the pun) in your car set up !!

 

[Uwe]

It does but the Gauge on the Cluster (not just VAG) is programmed the keep the driver happy not to give an Accurate reading.

Correct.

-Uwe-