DIY: Complete Coolant System Flush (the easy way)

[zz2h33]

DO this if you are running the green stuff, DO this if you have a mix of green and pink (brown), DO this if you're running original coolant with more then 50k miles.

I've seen several recent posts on this, and there doesnt seem to be an official DIY on here. So here goes:

This is the easiest and less messy way to do a complete coolant system flush (with heater core).

Drain coolant
1. Jack front end of car up enough to fit a bucket under the car, on the left side of the radiator core.
2. Place bucket under the lower radiator hose at the core.
3. Remove reservoir cap.
4. (3.0L only) Locate drain cock on lower radiator hose, near the core:


5. Open this drain cock, it will twist to the left 90 degrees then pull out a little, then twist again 90 degrees then pull out more. *Note, it does NOT pull out all the way! This will open the valve and the coolant will begin to drain on the side of the valve:



**If the drain cock is tight and doesnt want to twist DONT FORCE IT! You will most likely break the hose fitting and will need to replace it. Remove the lower radiator hose from the core instead by removing the clip on the top.

5a. (1.8L only) There is a sensor located in the same location that is clipped in, remove this sensor to drain the coolant.

6. Once coolant is finished draining into your bucket, close the drain cock same way as you opened it (push up, twist, push up more, twist).

7. Fill coolant reservoir with hot tap water.

8. Put resevior cap back on.

9. Start engine, put heater on "HI" temp, fan on low.

10. Let car warm until hot air blows from heater, then shut off the engine.

11. Slowly remove reservoir cap to allow system to vent slowly.

12. Drain coolant system again. *Note, reservoir cap must be removed for system to drain.

Repeat steps 4 - 12 until run off from coolant system is clear. You will notice the run off will become more and more diluted. Took me 4 times until mine was completely clear.

12. Once run off is clear and system is drained again, fill reservoir with STRAIGHT, undiluted G12 coolant. This is because when you drain the system, you are only draining about half of the full capacity (as you will see you drain about a gallon out each time). So, you have about a gallon of straight water left in the system. Thus, adding straight G12 will give you roughly 50/50 mixture. If your skeptical buy a freeze point tester and test the antifreeze mixture.

13. Replace reservoir cap and start engine. Heat on HI temp, fan on low. Let car warm up completely. If no hot air is coming from the heater, or the engine seems to over heat, the system will need to be purged of air (see below).

14. Shut engine down, let it cool for a bit then check coolant level. Top off as needed. Check at least 2 more times after driving the car. It should eventually take about a gallon of coolant.

To purge (bleed) air from the system:
- Wearing a good set of gloves, after engine has been running and system is warm, carefully and slowly remove the reservoir cap. The system will vent, gurgle, spit, etc. and you will notice the coolant level in the reservoir will drop.

- Top off with 50/50 mixture of coolant, replace cap, start engine and repeat until system is fully purged and coolant level remains full (heat works or engine doesnt over heat).

Be sure to dispose of used coolant properly.

[zz2h33]

Can an admin please post this in the DIY section? Thanks.

[akaEsCo01]

Nice write up, I just pull the hose, drains much faster

[Papachristou]

you can also bleed the coolant from the allen screw on the coolant line on top of the engine

[zz2h33]

^3.0's dont have the bleeder.

[widgget]

woooo, doing this tonight! thanks!

[AudiA4_20T]

1.8Ts dont have that drainer thing, we just pull out the sensor down there

[Papachristou]

^3.0's dont have the bleeder.

3.0s suck then just joking

but on a 1.8t its a great way to bleed it through the engine and all

[widgget]

1.8Ts dont have that drainer thing, we just pull out the sensor down there

correct, the sensor just comes out with a clip tho.

[zz2h33]

^fixed, note step "5a," can one of you 1.8 guys take a pic of this sensor so i can add it to the DIY?

thanks.

[widgget]

^fixed, note step "5a," can one of you 1.8 guys take a pic of this sensor so i can add it to the DIY?

thanks.

i'll take one for you tonight.

[lookaught]

Correct me if Im wrong but when you drain the radiator, even with the resevoir open not all of the coolant/water will drain. I dont know how much stays in the motor/heater core but it is significant. Filling with 50/50 will yield a net of less than 50/50, perhaps 40/60 (G12/water) or even 30/70.

Not that that is bad, as I think 30/70 is an acceptable ratio... but I just wanted to point that out. I guess if I knew the total coolant capacity (probably in the owners manual) and you measure the amount that drains out after the final flush you can calculate how much extra G12 to add, should you want the ratio to be 50/50.

Good write up! I cannot emphasize enough that coolant MUST be disposed of properly. It is extremely poisonous and kills a lot of cats and dogs every year. Please be responsible!

[lookaught]

1.8Ts dont have that drainer thing, we just pull out the sensor down there

My car is a 1.8t and has a petcock to drain the coolant.

I find that pulling the hose is more effective though, as the drain is slightly higher than the bottom of the rad so liquid still remains if you use on the petcock.

[widgget]

Correct me if Im wrong but when you drain the radiator, even with the resevoir open not all of the coolant/water will drain. I dont know how much stays in the motor/heater core but it is significant. Filling with 50/50 will yield a net of less than 50/50, perhaps 40/60 (G12/water) or even 30/70.

Not that that is bad, as I think 30/70 is an acceptable ratio... but I just wanted to point that out. I guess if I knew the total coolant capacity (probably in the owners manual) and you measure the amount that drains out after the final flush you can calculate how much extra G12 to add, should you want the ratio to be 50/50.

Good write up! I cannot emphasize enough that coolant MUST be disposed of properly. It is extremely poisonous and kills a lot of cats and dogs every year. Please be responsible!

I was wondering about this, since the dealer told me i woudl need two gallons of G12 to fill it back up, by the time i make it 50/50 i'm going to have 4 gallons of coolant......... i don't know where the hell they got their number from but i just don't see how i'm going to get 4 gallons into it. guess i'll mix it 60-G12/40-H2O before adding it back in.

[zz2h33]

^you guys are right, i missed this small but important factor. the cooling capacity in a 3.0L is 2.3 Gal (dry). When I drained using the drain cock i consistently got about a gallon out. So that means I should have added a gallon of straight G012. well, i used my trusty freeze point tester. Says its at -20F right now, 50/50 mixture should be around -30F. So i drained one more time, refilled with about a gallon of 50/50 and its right at -30F now.

revised the DIY already. whats the cooling capacity of 1.8L?

[zz2h33]

What do I need to do to get this moved to DIY section?

[Trev]

How about throwing some info in there about using a coolant flushing additive?

[ridelikeme]

dont use coolant flush additives with an Audi, different components and totally different corrosion rates. You can always flange up an aii compressor to blow the rest of the coolant out of the system

[A4TUNE]

well i have a question. I read that when you empty all the coolant you can put a water hose in the tank on top and leave the clip on the bottom open so it drains thoroughly. also i read that you can turn your car on while the hose is running and it will completely flush the system. can someone confirm if this is safe to do?

[rocketheavy]

i did that on my explorer and it work wonders :) not to sure on how you could do it on our cars without making a mess

[jeffrey146]

Correct me if Im wrong but when you drain the radiator, even with the resevoir open not all of the coolant/water will drain. I dont know how much stays in the motor/heater core but it is significant. Filling with 50/50 will yield a net of less than 50/50, perhaps 40/60 (G12/water) or even 30/70.

Not that that is bad, as I think 30/70 is an acceptable ratio... but I just wanted to point that out. I guess if I knew the total coolant capacity (probably in the owners manual) and you measure the amount that drains out after the final flush you can calculate how much extra G12 to add, should you want the ratio to be 50/50.

Good write up! I cannot emphasize enough that coolant MUST be disposed of properly. It is extremely poisonous and kills a lot of cats and dogs every year. Please be responsible!

or not.... use it to kill the strays... or your neighbors cat you hate

[incubusfc]

One other VERY important thing you want to do is USE DISTILLED WATER!!!!!!

Regular tap water will have impurities in it that will cause your system to rust much much faster than if you use distilled water. Yes, if you flush regularly on a shorter basis you can prevent this. I learned this lesson the hard way with my RX-7. I couldn't figure out why I had so much rust in the system, but it was from using hose water. Go to the store + get a few gallons of distilled water. It's only a buck or so a gallon, so why not?

[imnuts]

One other VERY important thing you want to do is USE DISTILLED WATER!!!!!!

Regular tap water will have impurities in it that will cause your system to rust much much faster than if you use distilled water. Yes, if you flush regularly on a shorter basis you can prevent this. I learned this lesson the hard way with my RX-7. I couldn't figure out why I had so much rust in the system, but it was from using hose water. Go to the store + get a few gallons of distilled water. It's only a buck or so a gallon, so why not?

Tap water will also have minerals in it that can build up in the system, forming deposits and causing the system to not work properly, or get clogged.

[subversion]

Will the system not circulate the fluid if you don't use hot water? I'm going to have to flush my coolant, again, tomorrow since I didn't use hot water when I did it today and it turned brown after I drove it.

[incubusfc]

That's not correct. Using hot water will just get it to warm up and open the thermostat faster. When you open the t stat it will circulate coolant through most of the passages. If you use cool water it will just take a while longer.

You want to flush it with straight distilled water several times. I did mine 4 times and it's still brown.
I bought a ton of it at the grocery store. I used about 1.5 gal per flush. If its just straight water just let her sit and run w the heat up and fan on low for several min the pull the clip on the temp sensor and stand back with the motor off. It'll pop from the pressure and then you can cap it off, fill and repeat.

[subversion]

That's not correct. Using hot water will just get it to warm up and open the thermostat faster. When you open the t stat it will circulate coolant through most of the passages. If you use cool water it will just take a while longer.

You want to flush it with straight distilled water several times. I did mine 4 times and it's still brown.
I bought a ton of it at the grocery store. I used about 1.5 gal per flush. If its just straight water just let her sit and run w the heat up and fan on low for several min the pull the clip on the temp sensor and stand back with the motor off. It'll pop from the pressure and then you can cap it off, fill and repeat.

Thanks. I'm guessing I just didn't let it run long enough with the cool distilled water I used since I never saw it circulate. I'm going to go at it again tomorrow with boiling water and hopefully get better results.

[subversion]

One final question: after driving the car, will the coolant ALWAYS pour out of the bottom of the reservoir when you unscrew the cap or only when there's air that needs to be purged? I purged it one last time after I drove on the highway and even though the temp gauge didn't budge even at 80 mph for 20 minutes, and the heat on HI was hot enough to burn my toes, the reservoir still purged fluid. Though, I didn't really hear hissing when I unscrewed the cap.

[tuesdayninja]

How long does it take your guys cars to blow hot air? It seems mine blows cold for ever. The first flush took 40 minutes to blow hot air, still on the second one.

[evo_ski]

I had a large enough bubble in mine that it did the same thing and would not blow hot air. I simply drove it around the block very easily, came back and the big bubble came out. Then after that it would blow hot air. Just take it for a really easy drive and you should be good.

[incubusfc]

Sub- yes. When the coolant gets hot it expands. So even if there's no air in it you will get some to purge when you open it and it's warm. I probably wouldn't do that because you may need to top it off sooner. Just keep an eye on it like you do your oil and top off the res when it's cold.

Tuesday- mine did t take that long. I would go for about 10 min the flush it. Remember to have the heat on high and the fans on low. If fans are on high then you're basically helping the coolant stay cool. Drive around a bit too- that will help it warm up faster too.

[Charles.waite]

If you open the reservoir cap REALLY slowly you can feel where the pressure point is. Once you get to that, back it off slowly until you can hear pressure releasing. If you let the pressure release slowly you'll generally avoid the purge out the bottom. The problem is when you release it quickly and a bubble comes out, the pressure fluctuation triggers the purge.

Also I've got the drain valve too on my 1.8t. 2004 if that matters...

[subversion]

Sub- yes. When the coolant gets hot it expands. So even if there's no air in it you will get some to purge when you open it and it's warm. I probably wouldn't do that because you may need to top it off sooner. Just keep an eye on it like you do your oil and top off the res when it's cold.

Tuesday- mine did t take that long. I would go for about 10 min the flush it. Remember to have the heat on high and the fans on low. If fans are on high then you're basically helping the coolant stay cool. Drive around a bit too- that will help it warm up faster too.

Thanks. It's been over a week since I flushed it and I haven't had any issues with the coolant temp or levels. I haven't tested the heat since it's been 90 F here the past few days, but I'll test it on a colder night to make sure it works. I'm sure it will since I didn't have any problem after flushing it.

[evoIX 2 audiA4]

Can someone take a picture of the bleeder valve? I will be doing this during the weekend and would love to know exactly where it is located. ;) Thanks!

[VectorG]

Well this will be my project for tomorrow yay

[VectorG]

Flushed mine and burp it and now it roast me out, my Core was clear i think i just had Air in mine.

Also isnt the G12 purple or pink? My car has Orange in it like the Dex-Cool stuff

DROID RAZR MAXX

[incubusfc]

The bleeder valve is under the engine cover. Take that off, then you'll see a somewhat large black metal pipe to the right of the valve cover. It's got a small flat black bolt that is either 5mm or 6mm Allen (hexagon.) that's your bleeder. Don't take it out all the way. Half- to a full turn works.


Does anyone know where the drain on the motor is for the 1.8t? I've flushed mine several times and I'm still getting rust.

[alexandermjoyce]

stupid, stupid question.. but how in the lord's name do you pull the sensor without breaking it?
they're horrible.

[MNAudi101]

sometime you have to work it a little, dont put too much pressure on it and it wont break

[alexandermjoyce]

sometime you have to work it a little, dont put too much pressure on it and it wont break

still, just pull on it?
is using a screwdriver like any VW sensor/clip necessary? there's a ring on it as well, it doesn't move and i know it's going to break.

[alexandermjoyce]

ohhhhh i got it...



thanks, for the write up.