T6 204 Coolant going then coming back.

[c_paul]

I have an interesting problem and would appreciate inspiration.

My van (2016 Caravelle 204ps, 53k miles) has developed a coolant problem.

Symptoms / points known so far from non-invasive investigations:

• Has alerted no coolant a few times shortly after engine start when still cool
• During alert, coolant tank is low but not empty
• When opening the tank (even when totally cold and been siting for days) system is under pressure and coolant returns into tank back up to normal level
• If I start / run the van after letting the coolant return to the reservoir it doesn’t disappear again for a unpredictable period of time.
• I have been unable to determine if it is actually losing any coolant as the level changes so much. But water is not known for it compressibility so must be going somewhere.
• It is due a service, last oil change was about 10k miles ago. Coolant was last changed 3 1/2 years ago, isn’t that dirty but it isn’t perfect. After starting it is slightly cloudy with perhaps a tiny brown tinge.
• No mayo on dipstick
• Van has always had mayo in filler cap; but I would subjectively say this is now worse.
• Van has always used oil, at the upper end of VWs spec but dealer said that it is normal.
• Regen happens more frequently than I think it should. Perhaps every 150 miles.
• EGR valve was replaced under warranty by dealer at 37k but they wouldn’t say why.
• No obvious soot or smoke of any kind
• No obvious smell of combustion gases in reservoir, I haven’t done a CO2 test yet to check more scientifically.
• When running and for a few minutes after stopping bubbles come through the pipe into the reservoir tank
• The rear heater doesn’t produce any heat. I don’t know if this is new.
• I haven’t done a compression test yet; however if it is holding pressure when cold it would suggest no significant leak
• No obvious leaks or wet patches

Not sure where to go next.

My thoughts are it is either egr cooler or head. Most likely head. Either way expensive.

Any suggestions?

Has anyone got any ideas on how to rule out either without significant investigation?

Is it worth investigating now or keep using the vehicle to gather more evidence / see if it gets worse? Or am I at risk of becoming a smart-motorway statistic / trashing the engine completely?

Thanks in advance,

Chris

 

[c_paul]

Small anecdotal addition that might be worth a mention.

A few times, the vehicle has ‘hiccuped’ as its turning over from cold. Started turning over but then paused for a fraction of a second on one cylinder as if it were hydro locked. Engine started immediately as this happened. Battery is well charged and in good shape.

 

[mmi]

When opening the tank (even when totally cold and been siting for days) system is under pressure and coolant returns into tank back up to normal level

When cold there shouldn't be any significant pressure (mine doesn't have). Sounds like there is a significant amount air in the system.

The rear heater doesn’t produce any heat. I don’t know if this is new.

Either air in the system or heater flap is stuck. The latter should be easy to verify.

Coolant was last changed 3 1/2 years ago, isn’t that dirty but it isn’t perfect.

A bit curious why the coolant was changed?

EGR valve was replaced under warranty by dealer at 37k but they wouldn’t say why.

Only the EGR valve? I would think it has been full EGR system = valve+cooler as quite a few coolers have suffered coolant leak.

EGR needs replacing. HOW? Where can I find a Manual or who can give me advice.

Yesss, one more of this :) I noticed there where already quite a few threads like this. My EGR needs replacing and unfortunately I don't have the full funds for getting it changed by a mechanic atm. I used to work in cooling and heating systems so I know a bit how to work with my hands. THe...

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Van has always used oil, at the upper end of VWs spec

How much is that, do you need add oil between oil changes?

Regen happens more frequently than I think it should. Perhaps every 150 miles.

Well, the frequency depends how the van is driven. Mine is performing the same by doing mostly 20 miles at a time at 50 mph. Some DPF regen statistics here:

[T6_measured] NOx emissions, AdBlue consumption, DPF regeneration - Before and after ECU update

Introduction An update campaign for T6 EU6 diesel engines took place in 2019-20. Affected engines were on van of model years MY16-MY18, including some of MY19. For M1 class (passenger carriers, VIN WV2...) the update was an official recall. For N1 class (VIN WV1....) the update was not...

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Any suggestions?

Perhaps the first step would be to bleed the coolant system?

 

[c_paul]

Thanks for the feedback thus far.

When cold there shouldn't be any significant pressure (mine doesn't have). Sounds like there is a significant amount air in the system.

yes - but how has it got there? And from what I can tell it is still getting in. I did std bleeding and it has just come back. The only bit I didn’t bleed was the rear heater matrix as I haven’t figured a way of doing that without removing half the car. Yet.

A bit curious why the coolant was changed?

Cambelt and water pump at scheduled interval. I assume they changed the water.

How much is that, do you need add oil between oil changes?

I haven’t worked it out exactly. It varies massively based on type of driving but I would guess 1l / 1000miles when doing 80 in europe. Probably 1l / 2000 miles when doing mixed slower driving on uk roads.

One thing I would add, the fuel economy is disappointing. I get about 30mpg when cruising at 70. Long term average is 28. Best I ever got was exactly 40 when slipstreaming a grit lorry for 20 miles on a country lane. But I have a heavy right foot.

 

[mmi]

I did std bleeding and it has just come back.

Just double-checking - as per VW engine workshop manual? Using a proper diagnostic tool to run engine, valves, flaps and electric pumps? I guess all that is needed as the engine actually has two (interconnected) coolant circuits - even separate radiators for low and high temperatures. Also having auxiliary heater (Webasto) and/or rear heater add the complexity of the circuits.

Chapter 19 in

T6 - 4-cylinder common rail engine CXEB CXFA CXGA CXGB CXHA CXGC CXHB - History

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[Dellmassive]

sounds to me there is an airlock in the system


the bleeding procedure is complex and requires diagnostic tool to run the various pumps in order. . .

SSP 564 - The T6 2.0L TDi

VW Self Study Programme, Document 564 - The 2.0 litre TDI Engine In The T6 The introduction of modern, particularly efficient Euro-6 engines represents a central feature of the new T6. All units are equipped with Blue Motion Technology as...

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[DXX]

Possibly a leaking charge air cooler? That said any liquid does not compress, it can only be pressurised, for the visible volume to be reduced and then return without adding there must be an airspace within the coolant system.

(P1 x V1) / T1 = (P2 x V2) / T2

 

[MikeBravo]

Dear Paul,

what did you manage to find out about the problem?
What is the solution?

regards, Mike