Cooling system wont bleed. Air-locked? Bad water pump?

Hey all,

I have searched for like the past day and have not found any situation similar to mine, so if it's been covered please point me in that direction.

I finished up a k04 swap this weekend and went ahead and drained the radiator and filled it as much fresh coolant since the coolant in the car was looking old.

I filled up the coolant res, let it gurgle down until it wouldn't anymore and then I went ahead and fired it up and started waiting for it to get up to temp and for the fans to kick on and the thermostat to open.

The fans never kicked on. The coolant never dropped down anymore as if the thermostat had opened and started flowing.

I let the car get up to 210F before cutting it off and risking anything.

The upper radiator hose gets hot. The radiator gets hot. But the low radiator hose has been staying cool to the touch, maybe getting warm, but nothing like the temp of the radiator or upper hose.

My a/c blows cold. My heater blows hot.

I really have no idea what to do or what I'm doing wrong. There is no visible leaks coming from anywhere so I don't think I have a pressure issue causing air to stay stuck in the system.

I've tried jacking up the car on the passenger side where the coolant res is located and did the entire process of letting the car idle with the coolant res cap off and letting the car self bleed and still nothing.

Lower radiator hose is always staying cool to the touch and everything else is heating up.

Am I not letting the car idle long enough? I swear I feel like I let the thing idle for 30min or more. Could my thermostat have gone bad? Could the water pump have failed? Or am I over thinking this and just need to keep trying to bleed the system?

My car has 48k miles on it if that means anything to anyone.

Thank you guys.

-K

Have you tried a vacuum fill tool? Drain the coolant from the hose going to the secondary pump and top it off with the vacuum tool. Schwaben makes a good one, but you'll need a air compressor.

So I have never fully drained the radiator, but I have a major leak when doing the k04 swap. I just did a fill and when cranking the car, it sucked down the coolant.
Maybe you can pressurize the system and then release the pressure on the reservoir causing coolant to run back into it. If there is an air blockage, it should move with pressure.

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I bought a schwaben vac tool, worked great!

Thanks for the replies. I ordered a schwaben tool but in the mean time I’m still fiddling with it.

It’s weird, the rad hose remains cool while I have the car running with the cap off. I’ll turn the car off and the coolant drops a bit. I assume this means that air is getting out of the system. When I turn the car off the lower rad hose finally gets warm though, but doesn’t when it’s running.

I’m guessing it’s an air problem. Temps never exceed 210F even when running for a good 5-10min after reaching that temp.

I have the worst luck bleeding anything car related I swear. I just want to get this thing ready for the dyno and back on the road!


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Did you turn the heater on full hot with fan running while trying to bleed the system?

Mk6 Steve said:

I bought a schwaben vac tool, worked great!

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Not only does it work great, but it's even fun to use.

It's annoying that there's no way to easily drain all of the coolant from the car, but at least with this tool you can dump and fill a fair portion a few times and get most of the old coolant out.

It's so easy that if you've got a couple of gallons of coolant/water mixed you can drain what it'll drain from the secondary pump and then top it off while doing an oil change. Do this every 20k miles or so and you'll never need to completely flush and fill.

Short Bus said:

Not only does it work great, but it's even fun to use.



It's annoying that there's no way to easily drain all of the coolant from the car, but at least with this tool you can dump and fill a fair portion a few times and get most of the old coolant out.



It's so easy that if you've got a couple of gallons of coolant/water mixed you can drain what it'll drain from the secondary pump and then top it off while doing an oil change. Do this every 20k miles or so and you'll never need to completely flush and fill.

Click to expand...

My bleeder gets here Thursday. Hopefully that fixes my issue. I have no idea why my thermostat or water pump would decide to take a crap on my right now but that would be my luck haha.

So do you drain it from the secondary pump only or do you pop off the lower rad hose too?


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ksandman said:

My bleeder gets here Thursday. Hopefully that fixes my issue. I have no idea why my thermostat or water pump would decide to take a crap on my right now but that would be my luck haha.

So do you drain it from the secondary pump only or do you pop off the lower rad hose too?


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The lower radiator hose is too much of a pain to get to. That and because it's about a third of the way up you can't completely drain it while it's on the car. So I flushed mine out by draining it from the secondary pump, vacuum filling it, let it idle for long enough to get coolant flowing through it, let it sit for 20-30 minutes, then repeat. I had about 100k miles on the factory fill and I want to say it was at the fifth or sixth time the coolant came out looking brand new.

The issue is that because there's no way to get 90% or more of it out all at once you have to take what you can get and keep diluting what's left until you're happy with it. So because you want it to cool a bit before you drain it, not only for your own safety but also because the main water pump is made of plastic that I suspect isn't happy if the coolant is replaced by superheated air.

In your case if you know most of the coolant is fresh, I'd just drain it from the secondary pump straight into a clean bucket, add more water/coolant misture to be sure the vacuum tool will remain completely submerged the whole time (don't want to add your own air), and just hope that does the trick.

Oh, and another fun thing about this tool is if you have any coolant leaks you'll know because it won't hold pressure and your compressor will have to keep running.

Do any of y’all monitor oil temps and coolant temps? If so, what are y’all reading? I feel like mine are a bit high but from what I’ve read on here, they seem to be lower than what other people are saying theirs cars operating temps are.


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ksandman said:

Do any of y’all monitor oil temps and coolant temps? If so, what are y’all reading? I feel like mine are a bit high but from what I’ve read on here, they seem to be lower than what other people are saying theirs cars operating temps are.


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My coolant stays at 190 and i monitor my oil through my Access Port and it stays between 205-215, depending on outside temperature. It may go higher than that but it hasn't been above 50 degrees F since i started monitoring.

At idle mine hits 221 F and drops to 213 F, then climbs again. Reported via Torque.

bumping an old thread. Hoping someone can shed some light on this issue and if the OP solved it. I’m having the exact scenario in my S3