Coolant Filling Problem

[Derek33]

Hello, I am looking for some help with a coolant filling issue that I am struggling with. I will let you know what I have done and what has happened. I imagine that some of you will have had similar experiences and/or may have suggestions.

I drained the coolant per the manual’s instructions (I have all of the erWin manuals for the vehicle, which is a 2015 Q5 3.0 TDI). There are two locations to drain from: (i) the lower radiator hose drain plug, and (ii) the upper radiator hose (which gets detached from the engine side). After everything was drained, I used compressed air to push a bit more out. I tightened the drain plug and reattached the upper radiator hose. I then hooked up an OEM 24444 vacuum tool to the coolant expansion tank. While drawing the system down to the proper vacuum, I primed the vacuum tool (so there would not be any air in the line that allows the new coolant to flow into the cooling system). With the line primed and the gauge at -26, I let it sit for a minute to make sure that the vacuum held, which it did. I allowed the new coolant to be pulled into the system (it drew in ±2 gallons). I removed the vacuum tool, filled the reservoir to the top, and opened the bleed screw on top of the EGR. With the bleed screw open, a small amount of air came out before coolant started to come out. I then replaced the bleed screw, topped up the reservoir and put the cap back on the reservoir. The manual says to then start the vehicle, make sure the heater is on full heat with a fan speed of low, run the vehicle it at 2000 RPM for 3 minutes, then let it idle until the upper and lower radiator hoses are warm, then to run it at 2000 RPM for 2 minutes, then to shut it off, let it cool and top up the reservoir to the proper level.

I did this, however, after idling for 25 minutes, I still did not have warm radiator hoses and the engine itself was very hot to the touch (burn-your-finger hot). I opened the oil filler cap and there was some smoke starting to come out. I believe that the engine was too hot to continue to operate, so I shut it off. I let it sit overnight and did the same process, starting with the 2000 RPM for 3 minutes and then letting it idle for another 20+ minutes until it was smoking hot again.

There it stands. What am I doing wrong?

I had no issues prior to draining the coolant.

I can feel coolant flowing in the heater hoses (so I am confident the water pump is pumping.)

I tried squeezing (multiple times) all of the different cooling hoses around the engine during the idling period.

The temp gauge inside the vehicle gets up to about ½ way between hot and cold.

Thank you!

[TexasDfwS4]

Shooting air into the system might have defected the thermostat?

[Derek33]

Geez, I guess that is a possibility. The system operates under pressure and it seems strange to me that blowing air through the system would have messed it up, though it could have. Along your line of thinking, there is definitely the possibility that the thermostat is not opening. Thanks for commenting!

Does anyone know:
(1) if the system is poorly bled (and there is an air pocket), does the thermostat still open?
(i) if the thermostat does open, wouldn't it just push the air pocket into the fill reservoir, or is there actually an air lock?
(ii) if the thermostat does open, wouldn't the upper radiator hose still get some flow through it, even if there is an air pocket?
(iii) if the thermostat doesn't open, is it due to the air pocket being on the wax element of the thermostat? (or possibly that it is faulty and is stuck shut)

The bleeder location on my vehicle is on the EGR. It is almost directly above the thermostat. If you look at a picture of the thermostat housing and how it is constructed, it looks like it would be nearly impossible for there to be an air pocket around the thermostat if coolant is coming out of the bleeder hole.

I am now noticing that the cooling fans are on as soon as I start the car (AC is turned off). I don't think that is normal.

I ordered a VCDS and plan on checking for codes (although I do not have a CEL that is on.)

[sQ5inSD]

assuming no mechanical components have failed it is most likely there is air trapped in the cooling system so despite how much of PITA it is you probably need to just drain the coolant and re-do the vac fill process - the OEM vac tool you have is the "best" but it is still possible to have just enough air trapped to cause the result you have

[Derek33]

Thank you for the comment!

It's not too bad to drain and re-do. Getting to the engine side of the upper cooling hose is the hardest part because it is a little buried in there, but not too bad... I've done it twice. Same result both times...

The fact that the cooling fans are coming at startup means something isn't right. I hope to know more once I have the scanner, and I will also be able to monitor engine oil temp during the warming up of the engine...

[Derek33]

We’ve got lift off!

The cooling system is running as it should. I hooked up the scanner and found codes for a misfire and a fuel injector, which I do not think are related to the cooling issue. I cleared the codes, started the engine and did the run-in process again for the coolant filling while monitoring oil and coolant temperatures. The cooling fans still came on immediately after startup. After the 2K RPM for 3 minutes, I let it idle. After 30 minutes I was only at 60 C for coolant temp and 62 C for oil temp. I started running it again at 2K RPM to try to speed things up. I was expecting/hoping that we would get to ±88 C and the thermostat would open, which did happen closer to 80 C. Engine hoses were all hot and good. Temp gauge stayed mid-way, which was ±80 C per the temp sensor.

Frankly, I am not sure what happened. I may not have had an overheating issue in the first place. It took a long time (way longer than I would have expected) to get up to operating temperature, which I imagine was impacted by the cooling fans being on. I am still not sure if the fans being on at startup is normal… Before purchasing the manual (and finding out about the bleeder on the EGR) I had done this process without unscrewing the bleeder. The engine got very hot to the touch, though I didn’t have the scanner hooked up or another tool to take an actual measurement of engine temp. I was definitely gun shy when I did the process again (knowing about the bleeder on the second round.)

I have attached a pic of the $600+ thermostat (which is incorporated into the oil filter housing). The manual says that this is a non-serviceable part (that the thermostat and/or gaskets cannot be changed and that a new one must be installed if this part is removed.) I have seen some gasket sets for it, but am not sure how easy it is to install them because there is an electrical wire connected to the thermostat (which is part of the MAP controlled aspect of it.) Using the part number, you can find some other knock-off options and see some better pictures. What I found interesting was that, because of the construction of the thermostat housing, and where the bleeder is located (which is pretty much directly above the thermostat) it seems impossible to have an air bubble around the thermostat if there is fluid coming out of the bleeder. I have also attached a couple of pics of the coolant reservoir and the bleeder location.

Thanks again for the help and support.

Bleeder.jpgReservoir and engine.jpgThermostat.jpg

[sQ5inSD]

I am not sure of the exact sensor number or its location but if your fans are turning on for cold starts look at the coolant temp sensor(s) it is possible the 3.0Ts have more than one, the sensor and/or its wiring may be faulty - also make sure your HVAC is set to off as well, the A/C compressor can run even if the heat is on in winter to send dry air for defogging the windshield - again I am not sure what the Q5 control logic is but many vehicles turn on the coolant fans whenever the A/C compressor turns on

[Derek33]

sQ5inSD, thank you very much for the input. Great comments and ideas. My vehicle does have more than one temp sensor. There is a cooling circuit for the cylinder heads that is separate from a cooling circuit for the cylinder block. Each has it's own temp sensor and is controlled independently. At cold startup, coolant temp, oil temp, coolant temp at radiator outlet, ambient temp and engine control temp are all showing values of more or less the ambient temperature. I am going to start a new thread for this particular question/problem.

[ozdi]

You forgot to bleed air at heater hose. You need to partly loose the inlet/outlet hoses to expose the bleeding hole on the metal ports.
Afterward, running the engine to do final bleeding as follows:

TIME: ---> ENGINE SPEED: ---> AC & HEATER SETTING:
================================================== ======

1 minute --> 2500 RPM ---> AC on, Heater all zones at HI

Until Radiator Fan Cuts in ---> Idling ---> AC off for the rest of procedure; Heater at 22 oC

1 minute ---> 2500 RPM ---> AC off; Heater at Hi

2 minutes ---> 2500 RPM ---> AC off, Heater off

1 minute ---> Idling ---> AC off; Heater off

1 minute ---> Engine Off ---> AC off; Heater off

1 minute ---> 2500 RPM ---> AC off; Heater at HI

2 minutes ---> 2500 RPM ---> AC off; Heater off

1 minute ---> Idling ---> AC of; Heater off


Turn OFF engine; Open the bonnet for cooling down 15~30 minutes; then repeat the procedure again.

Remember to check the coolant level and top up coolant when engine is cold.

VCDS has a feature for auto-bleeding but I prefer do manual bleeding for better control and can stop at any step.

[MSq5]

You forgot to bleed air at heater hose. You need to partly loose the inlet/outlet hoses to expose the bleeding hole on the metal ports.
Afterward, running the engine to do final bleeding as follows:

TIME: ---> ENGINE SPEED: ---> AC & HEATER SETTING:
================================================== ======

1 minute --> 2500 RPM ---> AC on, Heater all zones at HI

Until Radiator Fan Cuts in ---> Idling ---> AC off for the rest of procedure; Heater at 22 oC

1 minute ---> 2500 RPM ---> AC off; Heater at Hi

2 minutes ---> 2500 RPM ---> AC off, Heater off

1 minute ---> Idling ---> AC off; Heater off

1 minute ---> Engine Off ---> AC off; Heater off

1 minute ---> 2500 RPM ---> AC off; Heater at HI

2 minutes ---> 2500 RPM ---> AC off; Heater off

1 minute ---> Idling ---> AC of; Heater off


Turn OFF engine; Open the bonnet for cooling down 15~30 minutes; then repeat the procedure again.

Remember to check the coolant level and top up coolant when engine is cold.

VCDS has a feature for auto-bleeding but I prefer do manual bleeding for better control and can stop at any step.