Hmm. Do a compression test.
Also, stick a borescope down the bores to see if one looks different. And check the plugs for visual differences.
Also, pull both boost hoses to the intercoolers to see if one is unnaturally clean.
You can check to see if there are bubbles coming back from the radiator to the expansion tank. Should be a solid stream, IIRC. Might not be easy to see from the tank orifice. Can't remember how it is on the RS6.
Coolant leak (over pressuring)
Re: Coolant leak (over pressuring)
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
Re: Coolant leak (over pressuring)
Crackpot theory: Crack in turbo housing causing water loss, compression of coolant system and also loss of boost? It's a long shot but nicely covers all of your symptoms.
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
-
IchBautAuto
- 4th Gear
- Posts: 618
- Joined: Thu Feb 20, 2014 11:23 pm
- Location: Australia
Re: Coolant leak (over pressuring)
In reading the post, this is the only mention I have seen of the coolant tank cap. You'll all know that the temp and pressure are related. Also when conducting a coolant system vacuum test using my gear at least, it fits in where the header tank cap fits so that is the only component not tested.
Bottom line, if the cap is not holding the designed coolant system pressure then water will "vanish". This may not be the cause but I'd give it a jolly good look before doing some of the intrusive and time consuming test suggestions that have rocked up. Can't quite get why this hasn't been the No 1 check, even if it isn't a R8 cap.
C5 RS6, Milltek and Wagners: B5 RS4 450 + HP: A4 1.8 GP TQS original: 1963 UNIMOG 404:
Re: Coolant leak (over pressuring)
Maybe because it's too obvious?
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
Re: Coolant leak (over pressuring)
I've swapped the header tank and cap, but for a second hand/used one which I do not know 100% if its good, but I'd be surprised if both are faulty. When running for the first 30sec or so I saw no bubbles coming up into the header tank (then I put the cap on). CO leak tester should arrive tomorrow so I will run a check with that, I have a leak down tester as well, could try that.
This is all very annoying after it sailed through an MOT!
Also, it built up pressure in 2 mins of running, which I don't think i put enough heat into the coolant system to solely build that pressure thermally.
This is all very annoying after it sailed through an MOT!
Also, it built up pressure in 2 mins of running, which I don't think i put enough heat into the coolant system to solely build that pressure thermally.
Re: Coolant leak (over pressuring)
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
Re: Coolant leak (over pressuring)
Did you pressure test the cooling system when the car is cold? Don't do it when it's warm!
previous- Pug 205 gti, 306 gti, 309 gti Goodwood.
Audi S3, S4 V8 avant.
Porsche Macan Turbo.
Gone but NEVER forgotten - C5 RS6 Misano red avant.
Now - Empty garage
If you don't know where you're going, any road will take you there!
Audi S3, S4 V8 avant.
Porsche Macan Turbo.
Gone but NEVER forgotten - C5 RS6 Misano red avant.
Now - Empty garage
If you don't know where you're going, any road will take you there!
-
IchBautAuto
- 4th Gear
- Posts: 618
- Joined: Thu Feb 20, 2014 11:23 pm
- Location: Australia
Re: Coolant leak (over pressuring)
Touche! At least it gives something to think about other than fire and smoke.
C5 RS6, Milltek and Wagners: B5 RS4 450 + HP: A4 1.8 GP TQS original: 1963 UNIMOG 404:
Re: Coolant leak (over pressuring)
What pressure should the rad cap vent at?
Sent from my F8331 using Tapatalk
Sent from my F8331 using Tapatalk
Re: Coolant leak (over pressuring)
It's the headgasket, the funky blue liquid went yellow before the engine had warmed up!
Probably shouldn't try diagnosing the boost problem with it in this state.
Sent from my F8331 using Tapatalk
Probably shouldn't try diagnosing the boost problem with it in this state.
Sent from my F8331 using Tapatalk
Re: Coolant leak (over pressuring)
Fark. 
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
Re: Coolant leak (over pressuring)
Bugger, not very common on these engines I don't think. Fingers crossed there's not too much damage.
previous- Pug 205 gti, 306 gti, 309 gti Goodwood.
Audi S3, S4 V8 avant.
Porsche Macan Turbo.
Gone but NEVER forgotten - C5 RS6 Misano red avant.
Now - Empty garage
If you don't know where you're going, any road will take you there!
Audi S3, S4 V8 avant.
Porsche Macan Turbo.
Gone but NEVER forgotten - C5 RS6 Misano red avant.
Now - Empty garage
If you don't know where you're going, any road will take you there!
Re: Coolant leak (over pressuring)
I have my suspicions that the DPO may have had issues due to the volume of radweld k-seal I flushed out when doing the engine swap. I found the original radiator was split, and assumed that was why the grot was in there. In retrospect it may have been a split rad and the engine has overheated knackering the head gasket. Then DPO has applied bodgy gunk and punted it onto a dealer.
Arses! Engine out (again) then.
Sent from my F8331 using Tapatalk
Arses! Engine out (again) then.
Sent from my F8331 using Tapatalk
Re: Coolant leak (over pressuring)
Didn't you have the head off to fix the broken valve on this engine? Is this the other head?
Daytona RS6 C5 Avant. Viper'd, Billies, Waggers, MTM box brain, C6 stoppers, xcarlink, R8 coolant cap (woohoo)
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
///M3 E46 | XC90 (V8, natch) | Passat GTE | RR Classic V8 flapper
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."
Re: Coolant leak (over pressuring)
Holy crap, that's some bad luck. I've not followed your previous issues.
previous- Pug 205 gti, 306 gti, 309 gti Goodwood.
Audi S3, S4 V8 avant.
Porsche Macan Turbo.
Gone but NEVER forgotten - C5 RS6 Misano red avant.
Now - Empty garage
If you don't know where you're going, any road will take you there!
Audi S3, S4 V8 avant.
Porsche Macan Turbo.
Gone but NEVER forgotten - C5 RS6 Misano red avant.
Now - Empty garage
If you don't know where you're going, any road will take you there!
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