VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase

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Wed 14 Dec 2022 16:56
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Yudote

Have searched the forums for any other similar issues and couldn't see anything so thought I'd post and see if anyone can offer any advice:

  • Car: 2010 MK6 1.6 TDi Bluemotion
  • Mileage: 200,000
  • Last service: 10,000 miles ago (due fresh oil and filter)
  • Last coolant flush: July 21' - G12 used, no additives ever added
  • Coolant level: holding
  • Engine oil level: holding
  • Heaters: Working OK
  • Daily commute: 50 miles each way - motorway

Issue:

  • Since having the car I've never known the coolant gauge to go above 90. Until recently. When the engine was working relatively hard the other day, driving uphill, the gauge increased to around 100 degC before dropping back down to 90 degC on the flat. This was doing 75 mph.
  • Now I've been checking the oil temp when driving and notice it's quite a bit higher than normal. Average temp is about 108 and it has been as high as 118 when giving car some gas going uphill.
  • When I pull over after commute (50 miles) - the radiator body and top radiator hose are stone cold


Theory:

  • Water pump - don't think it is a failed water pump. If coolant wasn't circulating i'd expect the heater not to function and the engine oil to overheat quickly (no coolant flow through oil cooler)
  • Head gasket - car has done high mileage so this is a risk, but would not expect it to completely interupt flow of coolant to the radiator. Particularly when car is hot and idling, exhaust gas flow/pressure would be lower and less likely to interupt flow
  • Radiator - if radiator was fully blocked I'd expect there to be no flow and cold but struggle to see how it would fail so quickly
  • Thermostat - everywhere I read online people say thermostats fail open, i.e. car runs cold rather than hot. However the thermostat failing closed is the only thing i can think of that could be leading to no flow through radiator

Conclusion:

Replacing the thermostat is relatively inexpensive, I've had quotes for around £100 + VAT. Should I go ahead and get it replaced and see if it solves the issue or look for faults elsewhere?

Really appreciate any advice.

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Wed 14 Dec 2022 19:02
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - elekie&a/c doctor
On a cold day it’s possible the thermostat may not open fully. Replacing it may not fix the issue. Also don’t forget that when dpf regeneration takes place , engine temperature will increase slightly. I’m thinking there’s nothing wrong here .
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Wed 14 Dec 2022 20:01
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Yudote

Thanks but in pretty certain there is an issue. The oil temp at this time of year is normally around 95. I may change the oil and filter this weekend and see if that makes any difference.

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Thu 15 Dec 2022 12:34
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - edlithgow

2010 is newer than I've had experience of, but IIRC thermostat removal has been pretty trivial on anything I've had,

Assuming it isn't controlled by the ECU or something equally...er...modern, If you get it out you can check it with hot water and a thermometer.

Cant see how an oil and filter change is likely to fix this. If the filter is clogged it'll go in to bypass, but there'll still be circulating oil so I wouldnt expect much temperature shift.

I suppose if an oil passage was blocked, starving a bearing, that'd get hot, but if that were the case, fresh oil wont immediately un-plug it.

There would be some heating effect with heavily polymerised and thus high viscosity oil, but it would have to be very old and knackered for that to be noticable.

Edited by edlithgow on 15/12/2022 at 12:38

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Thu 15 Dec 2022 12:52
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Andrew-T

I may change the oil and filter this weekend and see if that makes any difference.

I think you have done well to get to 200K miles if 10K has been your regular oil-change interval. Makers are notorious for advising change intervals rather longer than is best for a diesel engine.

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Thu 15 Dec 2022 13:33
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - John F

I think you have done well to get to 200K miles if 10K has been your regular oil-change interval.

I would expect at least that mileage these days. Our last century VW Passat 2.0 GL petrol did over 240,000 miles, and its replacement Mk1 Focus 1.6 petrol was well past 160,000 when rust killed it - cheap oil and filter changed by me no fewer than 10-12,000 miles.

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Thu 15 Dec 2022 15:09
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Andrew-T

<< Our last century VW Passat 2.0 GL petrol did over 240,000 miles, and its replacement Mk1 Focus 1.6 petrol was well past 160,000 when rust killed it - cheap oil and filter changed by me no fewer than 10-12,000 miles. >>

Petrol, yes; diesel, perhaps not. Please read.

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Thu 15 Dec 2022 13:19
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - John F

Many years ago we had a similar problem with a son's Citroen Xantia - coolant apparently not circulating sufficiently. The diagnosis was failure of the (stupidly cheap) plastic impellor of the water pump. Its little paddles had almost disappeared. Perhaps your Golf is similarly equipped? Do please let us know the outcome.

Edited by John F on 15/12/2022 at 13:23

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Thu 15 Dec 2022 15:35
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - edlithgow

"Classically", you can see coolant circulation if you look in the filler port with the engine running.

Would take experience to determine if its less than expected, but it should be fairly obvious if there is almost none.

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Fri 16 Dec 2022 18:21
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Yudote

So just went to start car and the coolant level has dropped with earning light coming on. This throws my theory into disarray!

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Fri 16 Dec 2022 20:43
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - paul 1963

To me it sounds like the thermostat has stuck shut ( cold rad top after 50 miles) this has led to possible head gasket failure ( low coolant), any sign of mayonnaise on the oil cap, Bubbles in the expansion tank or moisture on the dip stick?

Any idea of where the temperature sender on it?

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Fri 16 Dec 2022 21:01
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Yudote

Hi Paul, no mayonnaise on cap and dipstick looks ok. Topped the coolant up tonight in the hope that there is a leak. Will leave car as is and check it tomorrow see if level is dropped. Car booked in for thermostat and oil and filter Tues. Have asked to keep thermostat and if it's a basic one hopefully be able to test if it's working. If head gasket gone afraid the old girl may have to be retired.

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Fri 16 Dec 2022 20:45
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - paul 1963

Double post...sorry chaps.

Edited by paul 1963 on 16/12/2022 at 20:45

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Fri 16 Dec 2022 21:18
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - elekie&a/c doctor
If it continues to lose coolant with no visible signs , I would get a combustion test done . If this proves positive, then it’s possibly an egr cooler issue . Not a cheap job .
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Fri 16 Dec 2022 23:23
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Adampr

Are these known to crack cylinder heads? It sounds a lot like my experiences with an old Hilux.

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Fri 16 Dec 2022 23:29
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Adampr

Have a look at this thread. It seems the heater matrix could also be the issue

www.vwaudiforum.co.uk/forum/showthread.php/188323-...e

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Sat 17 Dec 2022 10:18
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Yudote

Thanks guys for the responses very helpful. It does look like heater matrix could be the root cause. Sounds as though this particular model has an issue where if heater matrix gets blocked the thermostat doesn't receive enough hot water to open. I am ringing round garages for a quote. Just watched a recently uploaded YouTube video of a DIY and looks like an absolute pig of a job!

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Sat 17 Dec 2022 10:27
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - paul 1963

They normally are, I changed one on my old volvo years ago, took me the whole weekend, the complete dash had to come out.....Good that you've found the issue though, keep us updated.

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Sat 17 Dec 2022 11:08
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - elekie&a/c doctor
Not convinced it’s the heater matrix . These either leak or get blocked due to the additional “silikat “ bag fitted inside the expansion bottle that decomposes and blocks the water passage . ( check to see if this fitted to your car . Silikat will be stamped on the tank ) . If it’s loosing water , where is it going ?
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Sat 17 Dec 2022 16:01
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - galileo

Thanks guys for the responses very helpful. It does look like heater matrix could be the root cause. Sounds as though this particular model has an issue where if heater matrix gets blocked the thermostat doesn't receive enough hot water to open. I am ringing round garages for a quote. Just watched a recently uploaded YouTube video of a DIY and looks like an absolute pig of a job!

Years ago I had a Mk3 Cortina: the heater matrix was accessible under the bonnet, 2 screws held it ti the bulkhead and 2 Jubilee clips to disconnect the hoses. Took all of 10 minutes the change it. (control flaps were at the inner end of the duct)

I suspect these things are so inaccessible now to save cost/time at the factory or to discourage DIY and generate business for dealer workshops.

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Sat 17 Dec 2022 22:44
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - bathtub tom
Years ago I had a Mk3 Cortina: the heater matrix was accessible under the bonnet, 2 screws held it ti the bulkhead and 2 Jubilee clips to disconnect the hoses. Took all of 10 minutes the change it. (control flaps were at the inner end of the duct)

I had one of them in my impoverished days. When the matrix started leaking, I took it out and 'looped' the two hoses until I could afford to have it re-cored.

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Sun 18 Dec 2022 11:25
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - John F
Years ago I had a Mk3 Cortina: the heater matrix was accessible ...... Took all of 10 minutes the change it.

I had one of them in my impoverished days. When the matrix started leaking, I took it out and 'looped' the two hoses until I could afford to have it re-cored.

My 1980 TR7 has a really inaccessible heater matrix - the dashboard has to come out. If it ever leaks, I might do likewise. I think its patency and continence for over 40yrs is owing to my practice of never changing the coolant, thus denying the corrosion fairy a fresh supply of oxygen every so often.

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Sun 18 Dec 2022 12:16
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Andrew-T

<< I think its potency and continence for over 40yrs is owing to my practice of never changing the coolant, thus denying the corrosion fairy a fresh supply of oxygen every so often. >>

John, can you tell what colour your coolant is after all those years ?

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Sun 18 Dec 2022 12:44
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - edlithgow

My Skywing has the ultimate in inaccessible heater matrices, because it doesn't seem to have one.

I've looked.

Taiwan only car, so not really required except maybe on a few mountain passes in "not summer".

It MAY be possible to get heat from the aircon, if that was working. Dunno.

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Tue 11 Jul 2023 21:32
VW MK6 Golf 1.6 TDI 2010 - Mk6 1.6 TDI coolant/oil temperature increase - Yudote

Apologies for the delay responding.

So the problem was down to the heater matrix. Despite a number of garages questioning this I found a post elsewhere online of someone having a similar issue, replacing the heater matrix solving their problem. The same happened for me. Replaced the matrix and the gauge hasn't moved off 90. Engine oil temperature however does continue to run hot. I actually changed the thermostat as well, this made absolutely zero difference.

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