#1
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Coolant temp dropping.....
Doing my usual, twice monthly, drive between Lancashire and Heathrow.....
Driving home on Sunday evening, I hit a terrible jam on the M6 (no shocks there), which added about an hour to my journey. Not long after that sitting around I happened to notice my coolant temp gauge had just gone slightly to the left of 90 deg - it always sits dead centre once up and running, so this was a first. I continued to watch the temp fall to 70 and then work it's way to midway between 50 and 70 deg. I pulled into the Knutsford services and give her 5 minutes to sit with ignition off and then inspected the engine bay. I shone a torch into the header tank and the coolant was still pink and uncontaminated (I think I was half expecting an oil cooler fault chucking oil into the coolant!) Nothing else obvious to see either. So, I set off again (carefully) for the last 70 miles and initially the temp climbed a bit, but then resumed to the 50-70 range. My initial thoughts were thermostat stuck open or temp indication (sender). The next day, yesterday, did some local driving and the coolant got up to temp and sat nicely at 90. I think the next motorway run will tell the truth. I have priced up a new thermostat, but, then it was mientioned it could be the pump at fault? Any thoughts out there?
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Current: Graphite grey 2016 q7 3.0 (4m) Night blue - 2005 D3 4.2 TDi LWB My pride and joy - 1991 ur 20v quattro (owned since 2003). BMW 645 (Need to sell now I have 2 A8s....) Previous cars A8 D4 4.2tdi lwb (2011) A4 cab 3.0 Quattro petrol (2005) T5 Caravelle exec 2.5 (2006) A8 D2 3.7 quattro sport (2001) A8 D3 4.2 quattro (2003) A6 4.2 quattro avant (1999) A6 2.8 quattro (1998) Audi Coupe 2.6E (1993) Carlton 3.0 GSI |
#2
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Thinking about it, if the pump was an issue it would be 'getting hotter' rather than cooler.
So forget that ........ I think it will just be the thermostat - £60 approx from TPS, with housing.
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Current: Graphite grey 2016 q7 3.0 (4m) Night blue - 2005 D3 4.2 TDi LWB My pride and joy - 1991 ur 20v quattro (owned since 2003). BMW 645 (Need to sell now I have 2 A8s....) Previous cars A8 D4 4.2tdi lwb (2011) A4 cab 3.0 Quattro petrol (2005) T5 Caravelle exec 2.5 (2006) A8 D2 3.7 quattro sport (2001) A8 D3 4.2 quattro (2003) A6 4.2 quattro avant (1999) A6 2.8 quattro (1998) Audi Coupe 2.6E (1993) Carlton 3.0 GSI |
#3
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Does it seem like it's getting up-to-temperature? (ie engine feels hot, cabin heating still blowing hot). I had similar a similar issue a few years ago that turned out to be just the temperature sensor.
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Mark ------------------------------------------------------ 2002 FE S8 Ebony Black Pearl ------------------------------------------------------ ------------------------------------------------------ Cars Owned: The Tesla Era: 2020 Model S Performance Ludicrous+ (present) (Black, with all black premium interior and carbon fibre décor, 21" sonic carbon twin turbine wheels and FSD capability) The Audi Era: '97 A8 4.2 (Ming Blue) --> '96 A8 4.2 QS (Dark Green) --> '02 FE S8 (present) The Citroen Era: '84 BX 1.6 RS --> '89 BX 1.9 DTR Turbo --> '94 XM 2.0L Turbo --> '96 XM 2.0L Turbo Exclusive --> '00 Xantia Activa 2.0L Turbo The Banger Era: '76 1.2L Lada VAZ-2101 (Ruski Fiat 124) --> '80 1.7L Morris Ital HL, finished in Ermine White and Rust |
#4
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Yes - all appears normal.
I had an A6 a few yrs back and that had a failed coolant temp sensor - the car drove like a dog or even failed to start. It was cheap as chips to replace. Because the A8 is driving normally, I think I've discounted that, but, I'll keep it in mind- what's more, it's cheaper than the thermostat.
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Current: Graphite grey 2016 q7 3.0 (4m) Night blue - 2005 D3 4.2 TDi LWB My pride and joy - 1991 ur 20v quattro (owned since 2003). BMW 645 (Need to sell now I have 2 A8s....) Previous cars A8 D4 4.2tdi lwb (2011) A4 cab 3.0 Quattro petrol (2005) T5 Caravelle exec 2.5 (2006) A8 D2 3.7 quattro sport (2001) A8 D3 4.2 quattro (2003) A6 4.2 quattro avant (1999) A6 2.8 quattro (1998) Audi Coupe 2.6E (1993) Carlton 3.0 GSI |
#5
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Mine drove fairly normally too, if I recall correctly. I suppose it depends on how the sensor fails. If the sensor tells the ECU the engine's hot whet it's cold, I suspect that might cause cold-starting issues due to lack of enrichment. However, if the sensor tells the ECU the engine's cold when it's hot, it might cause the ECU to over-fuel the engine initially, but I suspect that feedback from the oxygen sensors and fuel-trim will compensate for that to some extent.
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Mark ------------------------------------------------------ 2002 FE S8 Ebony Black Pearl ------------------------------------------------------ ------------------------------------------------------ Cars Owned: The Tesla Era: 2020 Model S Performance Ludicrous+ (present) (Black, with all black premium interior and carbon fibre décor, 21" sonic carbon twin turbine wheels and FSD capability) The Audi Era: '97 A8 4.2 (Ming Blue) --> '96 A8 4.2 QS (Dark Green) --> '02 FE S8 (present) The Citroen Era: '84 BX 1.6 RS --> '89 BX 1.9 DTR Turbo --> '94 XM 2.0L Turbo --> '96 XM 2.0L Turbo Exclusive --> '00 Xantia Activa 2.0L Turbo The Banger Era: '76 1.2L Lada VAZ-2101 (Ruski Fiat 124) --> '80 1.7L Morris Ital HL, finished in Ermine White and Rust |
#6
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Quote:
Cheers
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Audi S8 D3 Facelift 2008. Phantom black pearl effect, Ceramic Brakes, 20 x 9J ‘7-arm twin-spoke’ design polished rims, ACC, Auxiliary heater, Side assist, Rear & side electrical blinds, Audi Parking System Advanced, Power boot, Soft close, Kessy, Auto dimming mirrors, Solar sunroof with photovoltaic cells, Bluetooth and Mobile phone with handset, Side & rear laminated glass, Leather & trim package 3, Bose 6000, Audi Music Interface, Digital TV & Radio, TPMS, Rear Climatronic, Front confort seats heated, ventilated & massage, Heated & electrically adjustable rear seats, Through-load facility, Tyre Mobility System & 19" spare wheel, Fridge, Alcantara package, Homelink, External lighting package. Wish list: B&O sound system, Rear ventilation + massage, RSE, MMI remote |
#7
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Let us know how you get on as my one takes lot longer to reach normal temperature these days.
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A8L 3.0 TDI sport executive 2014. Audi A2 1.4 petrol 2002 SOLD. Audi A8L 4.2TDI Silver 2006 Seat Ibiza 1.4tdi Eco 2008 Silver (£0 Tax)sold NO VCDS rely on Neeldub |
#8
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https://www.ebay.co.uk/itm/AUDI-A8-4...-/332302365216
4E0121113 This is the usual culprit, Audi call it a Coolant Regulator. I don't know about 4.2TDI location though but seems to be present on many VAG models, from Golfs to Bentleys, including our A8 3.0 TDI, W12 and others. Usually it's beside the gearbox where the coolant pipes enter it or behind the radiator near the bottom. When it fails, coolant can bypass the main thermostat and run through the radiator and autobox even when cold. Last edited by snapdragon; 19th April 2019 at 10:29 AM. |
#9
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Quote:
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A8L 3.0 TDI sport executive 2014. Audi A2 1.4 petrol 2002 SOLD. Audi A8L 4.2TDI Silver 2006 Seat Ibiza 1.4tdi Eco 2008 Silver (£0 Tax)sold NO VCDS rely on Neeldub |
#10
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They seem to fail more than the main thermostats but are cheaper and often easier to replace.
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