Author Topic: Golf Gti mk5 DSG - Has Mayo in Expansion tank? something to worry about?  (Read 208 times)

Offline ricky

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Hi Everyone,
I recently purchased a Gold GTI Mk5 DSG.
car has fsh and maintained well.
Only thing is recently i checked the expansion tank and it has mayo residue in there.
I know mechanic told me that unless you see it on the dipstick or the oil cap then it is just condensation build up.
Is this correct or is there something else much worse?
Appreciate any help and advise!

Offline LC5F

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Re: Golf Gti mk5 DSG - Has Mayo in Expansion tank? something to worry about?
« Reply #1 on: September 10, 2020, 06:43:25 PM »
For oil in coolant, normally the usual suspect is head gasket, but the ones on TFSI's are meant to be bulletproof...

I would say the most likely suspect would be one of the oil to coolant heat exchangers -one of them may have started to let go, pushing oil into your coolant.

The issue you have is there are 2 oil coolers -one on the engine and also the DSG box - it could be either.
Pretty hard to diagnose with the cooler in the car, it will need removal and pressure testing to confirm failure.
Also your coolant system will need cleaning to get the oil out.

At a guess I would say engine cooler - BTW you are unlucky, it is not that common for them to fail.

Offline Octoparrot

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Re: Golf Gti mk5 DSG - Has Mayo in Expansion tank? something to worry about?
« Reply #2 on: September 10, 2020, 07:42:16 PM »
For oil in coolant, normally the usual suspect is head gasket, but the ones on TFSI's are meant to be bulletproof...

I would say the most likely suspect would be one of the oil to coolant heat exchangers -one of them may have started to let go, pushing oil into your coolant.

The issue you have is there are 2 oil coolers -one on the engine and also the DSG box - it could be either.
Pretty hard to diagnose with the cooler in the car, it will need removal and pressure testing to confirm failure.

Also your coolant system will need cleaning to get the oil out.

At a guess I would say engine cooler - BTW you are unlucky, it is not that common for them to fail.

I agree with this, also I'd say the opposite of what your mechanic said, its normal for these engines to have a bit of mayo under filler cap or on the dipstick if used on short journeys.

Offline Stupots

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Re: Golf Gti mk5 DSG - Has Mayo in Expansion tank? something to worry about?
« Reply #3 on: September 11, 2020, 08:04:29 AM »
I agree with both previous replies... plus, go for the cheapest option first, which is the engine oil cooler anyway.

If it's the same as an Audi TT (my girlfriends) then it's attached to the oil filter housing. Her's also got mayo/oil in the coolant which first appeared in the expansion tank following a timing belt and water pump change. Reading on various VWAG forums suggested it wasn't unusual for this to happen after having the water pump changed but it seemed odd to me. Maybe the old water pump was inefficient and the new one had better pressure and caused anything close to failure to fail?

Anyways, I picked up a OEM oil cooler (she doesn't have DSG so one less thing to worry about) as dismantling the car, testing a part, ordering a part, waiting for it to arrive didn't seem like a good use of time. I then fitted it and flushed out the coolant system, replaced the oil and all has been good since. I never did test the old cooler, but seems to have been the culprit in my case. When you're pretty sure it's fixed you'll want to have the expansion tank off to give it a good clean, or order a new one, as the flush won't get the residue out of there.

In the back of my mind before and during the work was that it may be the head gasket, but as others say, these engines (Apart from the early BDK Diesels) are pretty much bullet proof when it comes to head/gasket issues and her's is the same engine they use for the 225 TT but is only running at 150, so I was fairly confident it wasn't that.

TLDR: It was the engine oil cooler and fixed for about £40 parts if I remember correctly.

Good luck

Stu
« Last Edit: September 11, 2020, 08:18:21 AM by Stupots »
VW Golf Mk5 TDI Sport 4Motion

Offline ricky

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Re: Golf Gti mk5 DSG - Has Mayo in Expansion tank? something to worry about?
« Reply #4 on: September 11, 2020, 12:23:36 PM »
I agree with both previous replies... plus, go for the cheapest option first, which is the engine oil cooler anyway.

If it's the same as an Audi TT (my girlfriends) then it's attached to the oil filter housing. Her's also got mayo/oil in the coolant which first appeared in the expansion tank following a timing belt and water pump change. Reading on various VWAG forums suggested it wasn't unusual for this to happen after having the water pump changed but it seemed odd to me. Maybe the old water pump was inefficient and the new one had better pressure and caused anything close to failure to fail?

Anyways, I picked up a OEM oil cooler (she doesn't have DSG so one less thing to worry about) as dismantling the car, testing a part, ordering a part, waiting for it to arrive didn't seem like a good use of time. I then fitted it and flushed out the coolant system, replaced the oil and all has been good since. I never did test the old cooler, but seems to have been the culprit in my case. When you're pretty sure it's fixed you'll want to have the expansion tank off to give it a good clean, or order a new one, as the flush won't get the residue out of there.

In the back of my mind before and during the work was that it may be the head gasket, but as others say, these engines (Apart from the early BDK Diesels) are pretty much bullet proof when it comes to head/gasket issues and her's is the same engine they use for the 225 TT but is only running at 150, so I was fairly confident it wasn't that.

TLDR: It was the engine oil cooler and fixed for about £40 parts if I remember correctly.

Good luck

Stu

That's interesting you say that as the car had a cambelt and waterpump change carried out recently.
SO maybe just that contamination. will flush the system and see if it goes away.
I hear the engine cooler is just a gaskit? and it labour intensive job?
Thanks for your help

Offline Stupots

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Re: Golf Gti mk5 DSG - Has Mayo in Expansion tank? something to worry about?
« Reply #5 on: September 11, 2020, 05:45:56 PM »
What I was saying was that a new water pump can cause an oil cooler to fail if it was close to failing. If that is what has happened then changing the oil cooler will sort. Flush after the issue is fixed. It's not contamination from replacing the water pump itself as that is solely connected to the coolant system.

I'm not sure how big a job it is on the Mk5... somebody else would be able to advise.
VW Golf Mk5 TDI Sport 4Motion

Offline LC5F

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Re: Golf Gti mk5 DSG - Has Mayo in Expansion tank? something to worry about?
« Reply #6 on: September 11, 2020, 08:35:31 PM »
I agree that new pump could be creating more pressure and push a near to failing cooler to fail.

Unsure how water pump replacement would create mayonnaise?
The water pump does not come into contact with oilways - I could understand an oil film forming in the header tank from the storage/anti-corrosion oil left on on the part - how bad was the mayonnaise? did you take a picture?

Usually coolers split internally, the cooler it is made up of thin alloy sheets separating oil from coolant.
Initially oil tends to push into coolant due to oil being at higher pressure than coolant.
Once its opened up it will continue to fail with the split opening up and coolant getting into oil may start to occur.

I would be keeping usage of the car down to minimum in case it fully lets go.
If you have to keep driving, scooping the mayo out and monitor closely to see if it returns.

Offline ricky

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Re: Golf Gti mk5 DSG - Has Mayo in Expansion tank? something to worry about?
« Reply #7 on: September 11, 2020, 09:40:32 PM »
I agree that new pump could be creating more pressure and push a near to failing cooler to fail.

Unsure how water pump replacement would create mayonnaise?
The water pump does not come into contact with oilways - I could understand an oil film forming in the header tank from the storage/anti-corrosion oil left on on the part - how bad was the mayonnaise? did you take a picture?

Usually coolers split internally, the cooler it is made up of thin alloy sheets separating oil from coolant.
Initially oil tends to push into coolant due to oil being at higher pressure than coolant.
Once its opened up it will continue to fail with the split opening up and coolant getting into oil may start to occur.

I would be keeping usage of the car down to minimum in case it fully lets go.
If you have to keep driving, scooping the mayo out and monitor closely to see if it returns.
It is my daily, so first i will clean out the tank. I have heard of short journeys can build crap in tank and see how it goes. Next will be the cooler replacement if it continues to happen. Thanks for your help.

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