# Oil Cooler Fail - oil in coolant



## Iceblue (Jul 20, 2018)

Hi all and just thought I would share the first issue with my 09 TT TFSI 2.0 S-tronic 95,000kms (58,000 miles), which may, or may not be helpful for other forum members. Having had the car for its last 20,000 kilometers with fairly brisk driving over an 8 month period I noticed a red coolant light come up on the DIS without an alarm. It took about 10 seconds before I had pulled over and switched the engine off during which time I looked at the temerature guage and noted it was not overheating and was sitting exactly on 90.

Because of this I restarted the engine and the warning light had gone off and did not come back on. I sat there for about 5 minutes at idle waiting for the light to reappear or for the temperature to move and nothing. Thinking this may be some computer glitch I kept driving the final 8 kilometers home and the next day drove 30 kilometers and saw the light come up again but with an alarm this time and pulled over again whilst confirming that the temperature guage was normal. I then checked the coolant. You can imagine my reaction and expletitives after opening the cap to find coolant that looked like mud (more cappucino colour) and after dipping a finger confirmed my worst thoughts - lots of oil in the coolant. My immediate thought was blown head gasket but could not work out why the car was sounding and driving really well with normal operating temperature. I then checked my oil and no oil registering on the stick (surprised no oil warning light had gone off) so immediately put in a litre which registered on the stick and rang my VAG indie. Told him symptons and he told me that it was probably the oil cooler. Now I know this may have been dumb (but had an important afternoon appointment that I needed to make) and after clearing it with the mechanic I removed as much coolant as possible with a rag and then topped up with bottled water and drove quietly to my indie 30k away without any warning lights and with normal operating temperature.

That was a week ago, and yes it was a failed oil cooler very much like the example in this youtube - 



 .

As I was about to book the car in for its second service under my ownership anyway, (has been regularly maintained before that according to log books and had a new cam belt and service done by the dealer when purchased) I asked my mechanic to replace the other oil cooler for the DSG (just in case) and to also check the cam follower (was OK BTW), replace existing with new NGK spark plugs, drain and replace all fluids and all filters (incl pollen) - based on advice from this forum. Anyway got the car back with a healthy labour bill largely as a result of the three to four times he had to prime and then flush out the coolant system of oil.

Any way good news everything seems to be running fine and actually feels better and more responsive although could be placebo effect. I am also checking the coolant regularly as no doubt some oil will still be in the system which if significant will have it flushed again.

My only concern was why did it fail. My mechanic said it was not unusual for VW's and I guess the youtube above confirms this. My issue however after searching this forum was I could find very few examples except for one in the Mk 1 section many years ago, and thought maybe it is not common for TT's.

Also does anybody know what other issues (apart from quality of the part) which may cause such a failure and at what intervals should oil coolers be replaced. I am also thinking that the coolant itself may have become corrosive (as Wolvez advised in a recent thread) so would encourage others to have it flushed/changed regularly to protect both your coolant system and oil coolers.


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## SwissJetPilot (Apr 27, 2014)

Audi doesn't require coolant change over the lifetime of the vehicle in their maintenance intervals, only "top up as required". I've verified the coolant flush with my local Audi service center and they also confirmed a flush isn't required. The coolant formulations have changed over years so they do perform better and are less prone to corrosion.

But I tend to agree with Wolvez, coolant chemistry isn't going to remain constant forever, especial with a car that's pushing 10-years or more on the road. A flush is good insurance despite what Audi recommends. Actually, the more I read in this forum, the less I trust Audi's service interval recommendations since any failure is to their advantage; Haldex filter, cam follower, etc. I bought a refractometer to check specific gravity of my coolant, but the more I think about it a pH test also makes sense using brand new coolant as a baseline.

As to the question of why the cooler failed, without a proper investigation, I'd be inclined to go with corrosion as the root cause. Having said that, you have to keep in mind the oil pressure is quite high as it passes through the cooler, so pressure, in combination with corrosion, is going to exploit any production defect or weakness. Coolers are just little radiators and are typically batch produced as you can see in this YouTube. Any bit of debris, lack of coverage, or inadequate coverage during the bath soldering process can lead to a pinhole or very thin joint which over time, will eventually fail.

I think for older vehicles, and especially those with high mileage, having the oil cooler (or at least the o-rings) replaced along with the water pump, and thermostat as part of a coolant system R&R, probably isn't a bad idea.






Any chance you can get you hands on the defective part? It would be interesting to open it up and inspect it.

I found this document on coolant. Seems to make sense -

View attachment VW_Audi_Coolant_Cooling_G12.pdf

Also, for anyone who wants to do this, here's now to replace the oil cooler -

https://sites.google.com/site/stoyneff/ ... eplacement


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## Iceblue (Jul 20, 2018)

Thanks Swiss and agree I think the coolant is an issue as identified by Wolvez and needs to be changed on are regular basis. I have the old oil cooler and the DMG one as well but the faiulure is within according to may mechanic so without any tools difficult to rip apart unless you have a small angle grinder.. He determined the leak using compressed air whilst bury the cooler in a bucket of water. Interesting there are minimal posts on this issue on the TT website so obviously a bit of a one off for TT's which was the most surprising aspect of the whole affair.


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## SwissJetPilot (Apr 27, 2014)

Another factor I failed to mention is vibration which can generate and propagate cracks. As noted, since the failure was internal, it would be impossible to detect a failure in this component in advance. The combination of mechanical and chemical effects on our vehicles' components will continue to take its toll especially as they get older and mileage increases.

It is a good lesson in why we need to regularly keep an eye on things we can see; coolant, oil, etc.

Here's the results of my coolant test -
https://www.ttforum.co.uk/forum/viewtop ... &t=1888169


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## Iceblue (Jul 20, 2018)

Thanks mate and am learning quickly. BTW I noticed a red stripe of some kind on your car from a photo you posted. Looks good on the silver roadster.


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## SwissJetPilot (Apr 27, 2014)

You mean these red stripes? Thanks.  Yeah, these tape stripes turned out okay. Bought them from Amazon*, 15-mm wide. I wasn't quite sure at first but I quite like 'em now. Just a splash of color and goes with my calipers. Next color effect will be yellow fog light lenses since they're legal here in Swissyland so we'll see how that turns out.










* https://www.amazon.de/gp/product/B00ODB ... UTF8&psc=1


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## Iceblue (Jul 20, 2018)

Suits the pre-facelift front end really well and look forward to seeing the yellow fog lights when you fit them


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## Wolvez (Jun 22, 2018)

It failed because it 's made of aluminum. Aluminum is prone to MICROSCOPIC CRACK. Most leak from a cracked cylinder head & Oil Cooler are misdiagnosed as head gasket problem. 



The reason why the Radiator, Heater Core and AC Evaporator is not failing is because they are ISOLATED from the Battery Negative Ground.

Dissimilar Metal + Electrolyte (Conductive Coolant) = Galvanic Corrosion


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## Iceblue (Jul 20, 2018)

Thanks Wolvez and accept it was probably corrosive coolant that could have been there for 10 years. As I am a ludite when it comes to the intricasies of these engines, is there a chance that the coolant got into my engine or other critical non coolant compatible parts when the oil cooler failed or would the pressure of the oil from the engine force the mixed coolant/oil back into the coolant system whilst the engine was running. I say this as there was no oil on the dipstick when I checked before putting in a litre to drive 30k to the mechanic so assumed the oil went into the coolant system and not the other way round. Is there anything else I need to worry about from that corrossive coolant noting that I had the DSG oil cooler replaced at the same time.


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## SwissJetPilot (Apr 27, 2014)

@ Iceblue - If you had a significant amount of coolant in your oil, it would most likely show up as thick, milky substance on the end of the dipstick. Some water in the oil is normal from condensation, especially in winter, and is usually observed as a "brown mayonayse" looking substance inside the oil filler cap. A normal drive at operating temperature for an hour or so will generally burn it off. So if you're in doubt, pull the dip stick, check the oil fill cap and check for color and consistency. If you're still concerned, get an oil and filter change for peace of mind.

Just to clarify what Wolvez is saying, the galvanic corrosion is not because the coolant is corrosive, but because of the effect of dissimilar metals being in contact with each other in combination with an electrical current in which case the coolant is acting as a conductor.

The TT's body work is a combination of aluminum and steel, and if not but together properly, galvanic corrosion will occur quire readily between the dissimilar metals as you can see in this picture of a steel screw onto an aluminum panel.

One example of how Audi gets around this for the body work is by using Dacromet-coated screws. This prevents the two metals from touching each other when bolted together and the coating prevents the steel screw from reacting with the aluminum. Read through SSP 383 (attached) to see some of the methods they use to put the TT body together. It's quite an engineering challenge.

Newer generations of coolant (e.g. G12 which we use) is generally pH neutral and is designed not to damage aluminum and magnesium parts. However people tend to top up their coolant with tap water which introduces all kinds of less than friendly chemistry into the coolant system. This is why you should NEVER top up with tap water. And for the radiator, it should be a 50/50 mix of G12 to water as defined in the instructions on the back of the G12 bottle*.

To be clear, G12 coolant is not going to directly attack the components of the cooling system. However, if someone has added tap water, it can throw off the chemistry and the minerals can act as a electronic transmission source between dissimilar metals by allowing the transfer of electrons from the aluminum to the steel. With the addition of production defects, microcracks, pressure and time, things will eventually fail anyway, but this just speeds up the process.

I read somewhere that on average, aluminum automotive parts have and expected lifetime of 10-years or 125,000 miles. Since most people never keep their cars this long anyway, component failure for a new car owner isn't really an issue. Only for "old timers" like us. 

View attachment Audi TT Coupe Body SSP_383.pdf


















*Manufacturers seem to have some difference of opinion between de-ionized and distilled water so be sure to read the back of the bottle if you use concentrate.


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## Iceblue (Jul 20, 2018)

Thanks again for the explanation and got it re coolant as a conductor regardless of mix because of lack of earthing to certain aluminium parts. On the coolant point however, I believe I had G12 as it had a first service with my mechanic who only uses the right VAG stuff I believe (We owned an A4 T 2009 wagon for 10 years and cabriolet 10 years before that) but he may not have checked what was in there was the right mix or topped it up much.

Strangely, there was never any colour on the dipstick even after I had driven it 30kms to the mechanic before which I topped it up with a litre after discovering no oil on the dipstick at the same time as oil in the coolant. Hence my asumption that the leak was one way only with the oil going into the coolant system not coolant going into the oil which goes to the engine.

Anyway as you have found, everybody who has a 10 year old car or older should change their aluminium oil coolers which includes the one for the DSG. Both cost me $600 AUD. BTW you are right about being an "old timer" I prefer Led Zepplin to Britney Speers :lol:


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## Wolvez (Jun 22, 2018)

if your engine is BWA or BPY, flushing the coolant will only clogged your radiator. VAG coolants are not compatible with one another. If G12 are really compatible with G13, why do they clearly say not to use G12 on vehicles with G13 coolant?

All coolants are slowly attacking the cooling system because they are conductive. The most anodic metal is slowly loosing electrons. To temporarily protect aluminum parts they are using Magnesium and Zinc as Sacrificial Anode.


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## SwissJetPilot (Apr 27, 2014)

EDIT - Post changed. See below.

https://www.wolflubes.com/EN_EU/Blog/20 ... olant.aspx


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## Wolvez (Jun 22, 2018)

SwissJetPilot said:


> You can't mix G12 with G13. The chemistry is different; G13 has glycerin added so it's environmentally friendly.
> 
> However, G13 is backwards compatible with the coolant system. So if you completely flush the system, you can replace G12 with G13.
> 
> https://www.wolflubes.com/EN_EU/Blog/20 ... olant.aspx


You misunderstood the chart. G12 and G11(Blue/Green) are the ones not compatible with one another. G13 is Backwards compatible with all types of coolant according to the TSB.

According to the paper/digital owner's manual the coolant type is G12+ but the coolant tank clearly says G12. The color of coolant is very misleading. G13 is color pink it will only looks like purple if you put it in a clear container and look at it against the light. G12 is not color red. 
[smiley=book2.gif]


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## SwissJetPilot (Apr 27, 2014)

Ah, okay. I stand corrected. Good catch, thanks!  I was under the impression that since G13 has glycerin, it wasn't compatible with G12.

As you noted, the coolant reservoir has "G12" marked on the side. Smart move in case one doesn't have the owners manual handy! This is a standard bottle used across multiple platforms so I suspect when the coolant chemistry changed, they didn't bother to update the mark on the bottles.

G12 DO NOT MIX WITH G11
G12+ Okay to mix with G12
G12++ Okay to mix with G12 or G12+
G13 Okay to mix with GE12, G12+ or G12++









Here's the TSB you referenced. [smiley=thumbsup.gif]


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## Wolvez (Jun 22, 2018)

SwissJetPilot said:


> Ah, okay. I stand corrected. Good catch, thanks!  I was under the impression that since G13 has glycerin, it wasn't compatible with G12.
> 
> As you noted, the coolant reservoir has "G12" marked on the side. Smart move in case one doesn't have the owners manual handy! This is a standard bottle used across multiple platforms so I suspect when the coolant chemistry changed, they didn't bother to update the mark on the bottles.
> 
> ...


Car manufacturers are pathological liars. The whole point why they are making new types of coolant and transmission fluids to make old cars obsolete. If they are really compatible, why do new cars with G13 coolant can't be filled with G12++?


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## SwissJetPilot (Apr 27, 2014)

I agree with you about VAG's lack of honesty with their customers.

The Haldex filter issue was a big tip off given the Borg-Warner company clearly stated not only did it have one, but it should be replaced at the same time the oil is changed. Meanwhile, Audi intentionally removed the filter from the parts diagram and the maintenance service intervals.

Then there's the fuel pump cam follower; no where it is mentioned and it's obviously not a "life-time" component any more than the Haldex filter.

I suspect many of these so called "design improvements" and "lifetime" components are nothing more than money making schemes. Actually, the oil cooler is a good example. It would be interesting to measure the in and out temperature of the oil just to see how effective it really is. And why not just have an air cooled oil cooler rather than the complexity of a water cooled unit?

Seems many of these "improved" parts have only one real function - to fail and cost us money! :x


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## Iceblue (Jul 20, 2018)

Wolvez said:


> if your engine is BWA or BPY, flushing the coolant will only clogged your radiator. VAG coolants are not compatible with one another. If G12 are really compatible with G13, why do they clearly say not to use G12 on vehicles with G13 coolant?
> 
> All coolants are slowly attacking the cooling system because they are conductive. The most anodic metal is slowly loosing electrons. To temporarily protect aluminum parts they are using Magnesium and Zinc as Sacrificial Anode.


Surprised they do not have sacrificial anodes that you can replace like they have on boats


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## SwissJetPilot (Apr 27, 2014)

They have sacrificial owners instead! :twisted:


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