Coolant Refill/Flush Question

[cztange]

In the middle of changing my PCV valve.. drained a bunch of coolant for it and trying to find some info on the forum for refilling the coolant system...

Do we absolutely have to use a vacuum tool to refill and get the air out of the system? I've searched the forum and youtube for info but can't seem to find anything.

[BR11S4]

You don’t have to. Bleed both supercharger screws and then heater hose by the battery terminals. Be careful with supercharger bleed screws. They like to break...


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[cztange]

You don’t have to. Bleed both supercharger screws and then heater hose by the battery terminals. Be careful with supercharger bleed screws. They like to break...


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Ok, so fill it up as full as I can, fire it up with the heater at max and fan low, then bleed from those points?

[BR11S4]

Ok, so fill it up as full as I can, fire it up with the heater at max and fan low, then bleed from those points?

There is a set procedure in the factory service manual. Can’t remember the entire process. But engine needs to be ran at 2k rpms. Heat on max, fan speed 0 (I think).

I don’t have my laptop with me. Have service manual on it.


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[MSq5]

There is a set procedure in the factory service manual. Can’t remember the entire process. But engine needs to be ran at 2k rpms. Heat on max, fan speed 0 (I think).

I don’t have my laptop with me. Have service manual on it.


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Yes, you may need to bleed it several times over several days, each time bleeding until clear coolant with no bubbles comes out of both s/c bleed screw locations. Bleeding from the heater hose bleed hole seems optional according to some, but I did that, too, just to be sure. Even with vacuum fill, air seems to get trapped easily in our system, even stock, but especially if you have added a larger HX or secondary reservoir. It is hard to get it all out.

You may never notice the presence of retained air unless you data log or monitor IATs. If they climb above the 60-65C range on long, full throttle runs, chances are good you still have trapped air.

Bleed thoroughly, drive a while, and then bleed some more. Eventually you will stop seeing bubbles when you rebleed. Then, you know you are done.

[Corydms7]

So you would just keep both screws open until coolant starts pouring out of them?

Yes, you may need to bleed it several times over several days, each time bleeding until clear coolant with no bubbles comes out of both s/c bleed screw locations. Bleeding from the heater hose bleed hole seems optional according to some, but I did that, too, just to be sure. Even with vacuum fill, air seems to get trapped easily in our system, even stock, but especially if you have added a larger HX or secondary reservoir. It is hard to get it all out.

You may never notice the presence of retained air unless you data log or monitor IATs. If they climb above the 60-65C range on long, full throttle runs, chances are good you still have trapped air.

Bleed thoroughly, drive a while, and then bleed some more. Eventually you will stop seeing bubbles when you rebleed. Then, you know you are done.

[cztange]

Thanks for the help guys, I've been posting lots here lately and I appreciate all the input!

[MSq5]

So you would just keep both screws open until coolant starts pouring out of them?

Sort of. Not only bleed until coolant comes out, but until the coolant is a constant stream of pure coolant, no bubbles. Do one screw at a time, as each is for a separate saddle tank.

[djn876]

They bleed separately but the intercoolers are connected via that front pipe, so they will fill simultaneously.

[Corydms7]

So how much coolant leaks all over the engine before the stream is pure? Wouldn’t the coolant go down the back side of the engine or something?

They bleed separately but the intercoolers are connected via that front pipe, so they will fill simultaneously.

[MSq5]

So how much coolant leaks all over the engine before the stream is pure? Wouldn’t the coolant go down the back side of the engine or something?

Do you want to bleed the air out or have hot spots in the engine (engine damage over time) and air trapped in the radiator or in the HX and reduce supercharger efficiency? Its that simple. Air bubbles in the be coolant mean you have not finished burping the system.

Get the air out. Yes, you will have some coolant drip from those bleeders and it may be a good bit before it is clear. Geez, just stuff some shop towels or even paper towels under and around the bleeders. You may have to change them once or more.

If bleeding an aftermarket larger HX with its own bleeder screw, you may have to bleed a long time just to get bubbles and may need to use a tiny funnel to keep adding coolant mix until it bleeds completely.

Sometimes, there is little air trapped and bleeding goes fast. Sometimes it takes repeated efforts.

Yes, it might get messy if you don't use shop towels or other absorbant material. It cleans up easily.

[djn876]

I just put a rag around the bleeder and it doesn't really make a mess.

Last time I did mine it didn't take long. I have a divorced system, so I filled up the AWE reservoir as much as it would go (fill everything slowly to help allow air to escape), jack the car up on the driver's front side to make it the highest point in the system, and run the SC coolant pump with VCDS while cracking the bleeders one at a time, I lost maybe a few ounces total of coolant during the process? This was with repeating a couple of times just to make sure it was done.

If you are not divorced, vacuum fill it and follow the factory bleed procedure, it works well.

So how much coolant leaks all over the engine before the stream is pure? Wouldn’t the coolant go down the back side of the engine or something?

[cztange]

The service manual procedure essentially says to fill the system with the vacuum tool, but I don't want to spend the $140 right now. Have you guys filled the system, then just bleed it while the motor is running? Like go up to 2000rpm and crack the bleeders on the S/C and the heater core etc.

[MSq5]

The service manual procedure essentially says to fill the system with the vacuum tool, but I don't want to spend the $140 right now. Have you guys filled the system, then just bleed it while the motor is running? Like go up to 2000rpm and crack the bleeders on the S/C and the heater core etc.

I have a vacuum filler (Schwaben) and know how to use it. I'm using it as directed. It's fast, but I still had to bleed the new hx, both s/c bleeders and the heater core to get rid of the bubbles (yes with engine running and thermostat open).

I expect most Stage 2 and higher tuners are encountering this and are confirming to their customers that while a little air in the system may be benign at stock and stage 1 levels, trapped air hurts IATs and performance in Stage 2 and higher cars in long full throttle muti-gear runs like full 1/4 mile runs. Its a fact.

[cztange]

I have a vacuum filler (Schwaben) and know how to use it. I'm using it as directed. It's fast, but I still had to bleed the new hx, both s/c bleeders and the heater core to get rid of the bubbles (yes with engine running and thermostat open).

I expect most Stage 2 and higher tuners are encountering this and are confirming to their customers that while a little air in the system may be benign at stock and stage 1 levels, trapped air hurts IATs and performance in Stage 2 and higher cars in long full throttle muti-gear runs like full 1/4 mile runs. Its a fact.

Not questioning your methods here, just wondering if it can be done without the vacuum tool that's all. I didn't drain the whole system by any means, just enough to get the PCV valve out and I was able to pour the amount removed back in. I will need to add more to account for losses from opening hoses and the PCV itself etc.. So just wondering if not refilling with the vacuum tool, and only bleeding from the S/C screws and heater core bleeder port is going to be enough.

I agree with trapped air being an issue, pure science right there, not questioning that.

[hardfive]

Not questioning your methods here, just wondering if it can be done without the vacuum tool that's all. I didn't drain the whole system by any means, just enough to get the PCV valve out and I was able to pour the amount removed back in. I will need to add more to account for losses from opening hoses and the PCV itself etc.. So just wondering if not refilling with the vacuum tool, and only bleeding from the S/C screws and heater core bleeder port is going to be enough.

I agree with trapped air being an issue, pure science right there, not questioning that.

Just did my PVC. Added coolant to reservoir and drained at SC screws only (didn't even do at heat exchanger). Temps are great. You'll be fine.

[MSq5]

Not questioning your methods here, just wondering if it can be done without the vacuum tool that's all. I didn't drain the whole system by any means, just enough to get the PCV valve out and I was able to pour the amount removed back in. I will need to add more to account for losses from opening hoses and the PCV itself etc.. So just wondering if not refilling with the vacuum tool, and only bleeding from the S/C screws and heater core bleeder port is going to be enough.

I agree with trapped air being an issue, pure science right there, not questioning that.

Yes, I used the "regular" method when I first went Stage 2. It was time for a flush and refill. I also wanted to run a higher water to antifreeze ratio. It worked fine. I got the vacuum filler when I installed the Merc HX a year later.

Both methods work. Vacuum fill is quicker, but I still needed to bleed everything. No need to buy a vacuum fill system. Its a convenience, not a necessity. More valuable when doing a complete drain/flush and refill.

My point was more that even vacuum fill often still leaves some air.

[jparedes]

I’m too scared to try to turn the SC bleeder screws and breaking them. I pulled back most of the rubber hose as far as I could on the left heater core hose in my B8.5 and didn’t see any hole for coolant to come out. Is it not that one? Is it the one on the right? I just let it bleed a long time from the Merc HX bleeder valve after vacuum filling. No idea how good of a job I did since I’m not logging shit.

[MSq5]

Not my car, but this is a good photo. The hose on the left is the one to bleed. You will see a small hole on top. You release the hose clamp enough to pull that hose back out until the hole opens. You can use a small finishing nail, toothpick or similar to push gently into the hole while pulling back. When back enough, the nail will enter the actual space. Remove the nail or toothpick and continue bleeding until coolant comes out. Continue until bubbles are gone and you get pure coolant. Then push the hose back in and reposition then clamp. This must be done with the engine running, heater on high, fans on low and the heater making heat.

As I suggested in another post, put a shop towel or some other absorbent material under the hose to catch the escaping coolant.

[adam044]

Not my car, but this is a good photo. The hose on the left is the one to bleed. You will see a small hole on top. You release the hose clamp enough to pull that hose back out until the hole opens. You can use a small finishing nail, toothpick or similar to push gently into the hole while pulling back. When back enough, the nail will enter the actual space. Remove the nail or toothpick and continue bleeding until coolant comes out. Continue until bubbles are gone and you get pure coolant. Then push the hose back in and reposition then clamp. This must be done with the engine running, heater on high, fans on low and the heater making heat.

As I suggested in another post, put a shop towel or some other absorbent material under the hose to catch the escaping coolant.

So now are you suggesting to bleed the 2 supercharger bleeder screws, the HX AND now this hose?

[01northernS4]

So now are you suggesting to bleed the 2 supercharger bleeder screws, the HX AND now this hose?

I'm not sure how important this hose is for the heater core... I did the 2 supercharger bleeder screws (pain in the ass, messy and risk breakage when hot) and the HX... I never did this hose, cabin warms up, great heat... I'll defer to the others on this... it is a separate circuit (engine cooling loop) and not sure how it can affect the supercharger loop as although they share the same reservoir (if not divorced) I believe once that air gets to the reservoir it's automatically burped out (hence having to periodically add fluid after a coolant flush for a period of time until it stabilizes). My reservoir burped a few times and I filled it up and now hasn't moved.

Those who know, can air be trapped in the engine cooling loop that doesn't autoburp and subsequently be introduced into the supercharger cooling loop?

If so, despite having great heat, I may try burping from this hose as well... just again sounds unnecessary.

[MSq5]

So now are you suggesting to bleed the 2 supercharger bleeder screws, the HX AND now this hose?

I was merely suggesting where that bleeder is located and how to use it. There are two separate threads going on this subject, so I'm not quite sure where we are.

I hold the view that if you are doing a full system drain/flush and refill, this heater hose bleed should be included. If you can't get hot air from the heater do it first. Usually, if you properly burp the reservoir, though, you'll get hot air.

If merely bleeding after installing an aftermarket HX, and preserving as much coolant in place as possible, its optional if you have good hot heat. Its also optional when doing repeat bleeding when you've already bled and think you still have air (high IATs).

However, since its easy to pull that hose back and bleed there as a final step, I have done it, anyway. When you think about it, Audi put that bleeder there for a reason. Whether air in the heater core has any effect on the supercharger loop, even indirectly, is debatable. I understand that point. But, why not do it? It is the highest bleed point in the system.

As to the supercharger screws, mine have been easy to turn, but I've turned them out a half turn first with the engine cold, "cracking" them, then back until almost tight but still turning easily, before starting the hot engine bleed. Its been easy that way and they don't leak until you turn them out more.

It really helps to find a big driver bit that fits them well. I'm OCD enough to have done this quite a few times, now, messing with different percentages of water to coolant - now 80/20 in favor of water, but going back to 70/30 or 50/50 when traveling north. Every time, I'm rebleeding. Those little plastic screws are doing fine. Maybe I'm just lucky. But, I think gently "cracking" them a bit cold is helping.

I'm by no means an expert on this. I'm merely reporting what I've been doing.

[01northernS4]

I was merely suggesting where that bleeder is located and how to use it. There are two separate threads going on this subject, so I'm not quite sure where we are.

I hold the view that if you are doing a full system drain/flush and refill, this heater hose bleed should be included. If you can't get hot air from the heater do it first. Usually, if you properly burp the reservoir, though, you'll get hot air.

If merely bleeding after installing an aftermarket HX, and preserving as much coolant in place as possible, its optional if you have good hot heat. Its also optional when doing repeat bleeding when you've already bled and think you still have air (high IATs).

However, since its easy to pull that hose back and bleed there as a final step, I have done it, anyway. When you think about it, Audi put that bleeder there for a reason. Whether air in the heater core has any effect on the supercharger loop, even indirectly, is debatable. I understand that point. But, why not do it? It is the highest bleed point in the system.

As to the supercharger screws, mine have been easy to turn, but I've turned them out a half turn first with the engine cold, "cracking" them, then back until almost tight but still turning easily, before starting the hot engine bleed. Its been easy that way and they don't leak until you turn them out more.

It really helps to find a big driver bit that fits them well. I'm OCD enough to have done this quite a few times, now, messing with different percentages of water to coolant - now 80/20 in favor of water, but going back to 70/30 or 50/50 when traveling north. Every time, I'm rebleeding. Those little plastic screws are doing fine. Maybe I'm just lucky. But, I think gently "cracking" them a bit cold is helping.

I'm by no means an expert on this. I'm merely reporting what I've been doing.

Excellent tip on cracking those supercharger bleed screws when the engine is cold. Great advice. Thanks for that!

[adam044]

Does the P3 gauge show IATs? Does anyone know? I know there is an air temp on it, just not sure exactly what that is reading

[01northernS4]

Does the P3 gauge show IATs? Does anyone know? I know there is an air temp on it, just not sure exactly what that is reading

Yes my buddy has it iat on the p3

[slacktide]

So now are you suggesting to bleed the 2 supercharger bleeder screws, the HX AND now this hose?

Bleeding the supercharger and HX only bleeds the supercharger side of the cooling loop. How else do you propose to get the air out of the engine block and heater core? They are not connected to the SC until the reservoir. This is the highest point of that system. This has been an Audi thing since forever. My old 1993 B4 had the exact same bleed hole.

Fyi, I bleed with the engine off and cold. Sacrilege, whatever, I’ve been doing it this way for 20 years. I use a rubber plug and shop air with a pressure regulator to pressurize the reservoir to 10 psi or so. Why deal with hot coolant if you don’t need to? It doesn’t need to be circulating , it only needs to be under pressure to drive the air out.

[BR11S4]

Yes. Bleed HX, then supercharger and then finically heater core hose. Heat on max, zero fan speed with engine at 2000 rpm.


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[SIQ5]

Following on this since I will be tinkering with my coolant ratio.

For my information, at what temperature is the thermostat (B8.5 SQ5) designed to open?

[wes8398]

Bleeding the supercharger and HX only bleeds the supercharger side of the cooling loop. How else do you propose to get the air out of the engine block and heater core? They are not connected to the SC until the reservoir. This is the highest point of that system. This has been an Audi thing since forever. My old 1993 B4 had the exact same bleed hole.

Fyi, I bleed with the engine off and cold. Sacrilege, whatever, I’ve been doing it this way for 20 years. I use a rubber plug and shop air with a pressure regulator to pressurize the reservoir to 10 psi or so. Why deal with hot coolant if you don’t need to? It doesn’t need to be circulating , it only needs to be under pressure to drive the air out.

IIRC from my HX install and full drain/flush/refill: I believe these cooling loops DO have a crossover point. I recall it being a small line with a "T" in it, which fed off to the SC loop. Whether air could escape one loop and make it to the other... I doubt it.

Regarding your method of bleeding.... what about the t-stat? Sure, if it's easily accessible, you can remove it for this process. But that's not exactly the case with the 3.0T lol

[MSq5]

Bleeding the supercharger and HX only bleeds the supercharger side of the cooling loop. How else do you propose to get the air out of the engine block and heater core? They are not connected to the SC until the reservoir. This is the highest point of that system. This has been an Audi thing since forever. My old 1993 B4 had the exact same bleed hole.

Fyi, I bleed with the engine off and cold. Sacrilege, whatever, I’ve been doing it this way for 20 years. I use a rubber plug and shop air with a pressure regulator to pressurize the reservoir to 10 psi or so. Why deal with hot coolant if you don’t need to? It doesn’t need to be circulating , it only needs to be under pressure to drive the air out.

If you are bleeding cold with the t-stat still closed you are not getting air out of the water jackets in the engine and cylinder head. Thats where dangerous hot spots can form. How do you plan to evacuate that trapped air?

[cztange]

So what I did after replacing my PCV valve, I didn't drain the whole coolant system but did get a fair bit out. Filled the resevoir and cracked the bleeder screws on the S/C. Heater on high with fan as low as it could go to get the thermostat open. Ran the engine til it warmed up, bled through both S/C screws and then the heater core hose. Had a partner run the engine at 2000rpm while doing so.

Refilled reservoir a time or two during this process, then took it for a drive. Took a couple drives around town in sport mode over a couple days to keep the motor over 2000, then let the engine cool off and topped up the coolant reservoir. Good to go now, level hasn't dropped and have good heat.

[Fast4esT]

if you can run the coolant pump at 100% with vagcom is it still necessary to run the engine at 2000rpm? im gonna start with using a vacuum tool to fill the system. I do have a Merc HX too.
im replacing water pump.
should I pinch off the hoses at the HX before I drain coolant from engine?