High pressure coolant leak and rattling noise. Help me diagnose

[Scorn5692]

Hi everyone,
I have a 2016 S5 B8.5 with 70,000 km/ 43,600 miles and wanted to share what sort of issues I recently experienced, my diagnosis, and what I’m planning to repair.
I would love to get a 2nd opinion on whether this is how you would tackle the problem or if this is what you would repair based on those symptoms.

• While driving, heard squealing noise. I pulled over, popped the hood open, listened to the engine, and heard a loud rattling noise
• A few days later, after a 20min drive, low coolant light came up, stopped, popped the hood open and coolant was flying all over the engine, impossible to locate the source, the whole front engine was wet, the radiator was wet, pipes, wires everything was wet/soaked. Topped up coolant to the MAX level to drive back home and by the time I got back home, low coolant light was back on, and coolant level was way below MIN level.
• At home, trying to find the leak, I noticed the water pump pulley moving side to side off its axis. Also when it moves the rattling noise seem to amplify.

I made a short 43s video broken down into 3 short clips of the 3 instances above so you can hear the rattling noise and see the coolant spraying all over the place.
https://www.youtube.com/watch?v=oluCa-aw1q0

My Diagnosis: I think the water pump failed causing the pulley to move sideways (what we see in the video). When the pulley moves sideways it creates a gap between the pulley and the water pump from which high-pressure coolant leaks from, which would explain why it’s flying over all over the place in a mist form.
I came across this video where a guy demonstrates how the new water pump has no play while the old one has a lot of play (where the red arrow is pointing at in the screenshot below). This is where I think my water pump also failed and where the high-pressure coolant is leaking from, what do you guys think?

What I’m planning to repair:
Water pump + new water pump pulley (sold separately)
Preventately replace thermostat since it’s just right next to the water pump.
Wondering if I should also replace the PCV valve?

Then in the front of the engine, I’m thinking of replacing supercharger/accessory belts,tensioners and idlers.

Any thoughts on my diagnosis and repairs? Would you do the PCV valve too? Anything you would replace I haven’t mentioned? Or am I dead wrong on my diagnosis?

Thanks in advance

[hahnmgh63]

Definitely the water pump. After removing the front bumper the front radiator suppor can be put into what is called the “Service Postion”. That is, it tilts outward from the top. All B8/B8.5’s years have been plagued with mixed quality of waterpumps, some fail early, some last a long time. The thermostat, even though it is close requires the removal of the Supercharger (not a big job but a lot of seals that would then need replacing). I’d just do the waterpump and belt and maye the plastic cross pipe (they get old and brittle) right by the waterpump pulley and call it good for now. Be ready to do the Thermostat in a year or two as your mileage increases and it will be closer to the time you will need a Carbon clean since you will already have the Supercharger off. Make sure you flush it well to get as many of the waterpump impeller pieces out if it has disintegrated too.

[Scorn5692]

Thank you @hahnmgh63

It was indeed the water pump. I just removed the water pump and thermostat today and I was on the money with regards to the point of failure, it’s been leaking through the bearings

See here we can see dried coolant being sprayed out of the water pump under pressure explaining why coolant was flying all over the engine

I’m going to replace the thermostat too, don’t want to have to redo it all

[hahnmgh63]

Congrats on the job. Feels good and if all goes well the pump should last 100k miles…hopefully. I do think the tensioner for the serpentine belt is a little tight on mine, maybe it is on all of them and is the root cause of the bearings untimely demise.

[Scorn5692]

Thanks man but I must be sadomasochist. After posting, I decided to go ahead and replace the PCV valve as well because I noticed coolant or oil at the bottom of the supercharger valley. Wasn’t sure if the PCV had gone bad but I didn’t want to risk reassembling everything and still experience coolant leak or something. Jokes aside.

It was a pain to get to the PCV, had to remove all the fuel lines in the way (double fuel lines on CREC engine) and then deal with that damn coolant pipe that sits literally right on top of the PCV valve! I mean why not make it go around to the left so we can take out the PCV without removing it

Anyway, I just removed the PCV valve, and here’s what it looks like. Is it normal to have coolant on the right and oil on the left at the bottom? But it does appear that oil and coolant was leaking outside the PCV to the bottom of the engine valley. What do you think? Has the PCV failed? (Just curious, I’m replacing it anyway)

[hahnmgh63]

The PCV assemblies do fail occasionally but usually not until 100k plus miles. There shouldn’t be coolant in the bottom, probably as you said, just dripped down while you were removing the PCV. How did your intake valves look as far as carbon with only 43k miles? You did have to remove the lower intake manifolds to get the PCV out didn’t you? Are you replacing all of the injector seals?

[Scorn5692]

Coolant didn’t drip when removing the PCV, it was like that when I got there before even touching the coolan pipe. If you look closely around where the PCV sits (not inside) you will notice a black liquid, all of that is flooded. I think the PCV itself was still ok but it was leaking through the gasket.
I don’t know it was pretty bad as such low mileage.

Intake valves looks good, I have the CREC engine with 2 injectors which help prevent carbon build up