Coolant leak or sweet smell: which faults cause it?

The most important among the documented faults: cracked expansion tank and coolant leak, in the BMW M54; cracked plastic coolant pipes on the Cayenne V8, in the Porsche V8 and V6 (Cayenne and Panamera); fragile water pump (and expansion tank or heat exchanger, depending on displacement), in the 1.4/1.6 VTi; fragile water pump and heat exchanger, in the 1.6 THP; coolant leak at the thermostat housing, in the 0.9 TCe; failing water pump and cooling system leaks, in the 3.0 TDI V6; electric water pump failure (BMW campaign in the US over fire risk), in the BMW N20; coolant loss from hoses, water pump or expansion tank, in the 1.6 EcoBoost.

LeaksUrgency: Garage soon

Coolant leak or sweet smell: causes and the faults that trigger it

31 documented faults cause it in 28 engines. The most important:

High severity: Cracked expansion tank and coolant leak · BMW M54
High severity: Cracked plastic coolant pipes on the Cayenne V8 · Porsche V8 and V6 (Cayenne and Panamera)
High severity: Fragile water pump (and expansion tank or heat exchanger, depending on displacement) · 1.4/1.6 VTi

What it means

Pink, green or blue stains under the car, crystallised residue on hoses or a sweet smell in the cabin point to a leak in the cooling circuit.

General explanation from MotorFiable. How it shows up in each engine, with sources, is in the list of faults.

What to do now

Garage soon

Check the level when cold and ask for the leak to be located. Driving with low coolant can overheat the engine in a short time.

Reviewed on 9 October 202642 sources How we work

Faults that cause it

Specific engine and gearbox faults, from most to least important (severity × frequency). Below each title, how the symptom shows up in that fault.

- High severityCommonFrequency: CommonBMW M54Cracked expansion tank and coolant leakVisible coolant leaks, a sweet smell and frequent low-level warnings.
Source for the symptom in the BMW M54^[1]
- High severityCommonFrequency: CommonPorsche V8 and V6 (Cayenne and Panamera)Cracked plastic coolant pipes on the Cayenne V8Dry coolant residue in the engine valley and, when it drips onto the starter motor, starter faults; a British forum adds that the fluid can reach the automatic gearbox bell housing.
Source for the symptom in the Porsche V8 and V6 (Cayenne and Panamera)^[2][3][4]
- High severityCommonFrequency: Common1.4/1.6 VTiFragile water pump (and expansion tank or heat exchanger, depending on displacement)Stains or traces of coolant under the engine, around the water pump or the expansion tank.
Source for the symptom in the 1.4/1.6 VTi^[5]
- High severityCommonFrequency: Common1.6 THPFragile water pump and heat exchangerStains or traces of coolant under the engine, in the area of the water pump.
Source for the symptom in the 1.6 THP^[5]
- High severityCommonFrequency: Common0.9 TCeCoolant leak at the thermostat housingStains or a drop in coolant level, often originating at the thermostat housing (calorstat) gasket, at the front of the block.
Source for the symptom in the 0.9 TCe^[6]
- High severityCommonFrequency: Common3.0 TDI V6Failing water pump and cooling system leaksLeaks from hoses, plastic fittings, the regulating valve or the cooler, according to owner reports.
Source for the symptom in the 3.0 TDI V6^[7][8]
- Critical severityOccasionalFrequency: OccasionalBMW N20Electric water pump failure (BMW campaign in the US over fire risk)Loss of coolant or a need to top up the reservoir more often than normal.
Source for the symptom in the BMW N20^[9]
- High severityOccasionalFrequency: Occasional1.6 EcoBoostCoolant loss from hoses, water pump or expansion tankIn other cases there are visible stains or crystallised residue on the hoses or under the car.
Source for the symptom in the 1.6 EcoBoost^[10]
- High severityOccasionalFrequency: Occasional2.2 TD4 / SD4Coolant leak from the EGR valve coolerCoolant leak in the intake/EGR area; the Evoque owner also spoke of exhaust gases in the cabin.
Source for the symptom in the 2.2 TD4 / SD4^[11]
- High severityOccasionalFrequency: OccasionalSubaru bóxerDamaged cylinder head gasket on the EJ petrol enginesExternal coolant leaks over the block, with greenish traces and a sweet smell, according to SlashGear.
Source for the symptom in the Subaru bóxer^[12]
- High severityOccasionalFrequency: Occasional2.0 and 2.4 VVT-iCylinder head bolt threads in the 2AZ-FE blockCoolant leaks and overheating.
Source for the symptom in the 2.0 and 2.4 VVT-i^[13]
- Medium severityCommonFrequency: Common1.2 and 1.4 TSIWater pump and thermostat housing leak (EA211)Coolant seeps on the gearbox side of the cylinder head, where the thermostat housing with the pump is mounted.Appears at around 80,000 km
Source for the symptom in the 1.2 and 1.4 TSI^[14][15]
- Medium severityCommonFrequency: Common2.0 TDICoolant loss from the water pump or the coolersLeak at the water pump or at the thermostat housing gasket.
Source for the symptom in the 2.0 TDI^[16]
- Medium severityCommonFrequency: CommonOM651Coolant leak from the thermostat connector and heat exchangerCoolant stains under the car or crystallised residue beside the cylinder head connector or the hoses.
Source for the symptom in the OM651^[17]
- Medium severityCommonFrequency: Common2.0 TSI / TFSIThermostat housing leak and water pump failureCoolant stains or crystallised residue around the thermostat housing, at the front of the engine.
Source for the symptom in the 2.0 TSI / TFSI^[18]
- Medium severityCommonFrequency: CommonBMW N62 / N63N63 coolant loss and cracks in the cylinder headLeaks from hoses and from the water pump in the owner reports collected by fiches-auto.
Source for the symptom in the BMW N62 / N63^[19]
- Medium severityCommonFrequency: CommonBMW N62 / N63N62 coolant loss from hoses and the pipe between the cylinder banksCoolant leak in the engine valley from the transfer pipe or the hose between the banks.
Source for the symptom in the BMW N62 / N63^[20][21]
- Medium severityCommonFrequency: Common1.0/1.2/1.4 EcotecWater pump and thermostat leak or wearCoolant stains or dripping under the engine, near the water pump.Repair (garage): €300–€760Appears at around 22,000 km
Source for the symptom in the 1.0/1.2/1.4 Ecotec^[22][23]
- Medium severityCommonFrequency: Common1.4 TurboCoolant leak from the water pump or thermostat housingIn the clearest cases coolant is visible under the engine, next to the water pump or the thermostat housing.Repair (garage): €350–€550Appears at around 28,000 km
Source for the symptom in the 1.4 Turbo^[24][25]
- Medium severityCommonFrequency: Common1.0 VVT-iCoolant leak from the water pumpStains or puddles of coolant under the car, or having to top up the coolant reservoir more often than normal.
Source for the symptom in the 1.0 VVT-i^[26][27][28]
- Medium severityOccasionalFrequency: Occasional1.0 TSI / 1.5 TSICoolant leaks from the water pump and thermostat moduleTraces of coolant around the water pump and thermostat, next to the camshaft adjusters.
Source for the symptom in the 1.0 TSI / 1.5 TSI^[29][30]
- Medium severityOccasionalFrequency: OccasionalAudi 3.0 TFSI V6Leak at the thermostat housing and water pumpCoolant leak, usually at the front of the engine, from the thermostat housing or the water pump.
Source for the symptom in the Audi 3.0 TFSI V6^[31][32]
- Medium severityOccasionalFrequency: OccasionalBMW B58Coolant loss from the cap or the expansion tankVisible traces of coolant on the engine or around the water pump opening.
Source for the symptom in the BMW B58^[33][34]
- Medium severityOccasionalFrequency: OccasionalBMW B58Water pump and thermostat module (thermal management) leakCoolant leak at the back of the engine and traces next to the pump's drain hole.Appears at around 120,000 km
Source for the symptom in the BMW B58^[33][35]
- Medium severityOccasionalFrequency: Occasional2.2 CDI (OM646)Leak and premature failure of the water pumpCoolant stains under the engine, around the water pump, radiator or hoses.
Source for the symptom in the 2.2 CDI (OM646)^[36]
- Medium severityOccasionalFrequency: Occasional1.6 and 1.8 Ecotec 16vCoolant loss through the thermostat or water pumpIn the clearest cases, coolant is visible under the engine.Appears at around 30,000 km
Source for the symptom in the 1.6 and 1.8 Ecotec 16v^[37]
- Medium severityOccasionalFrequency: OccasionalPorsche V8 and V6 (Cayenne and Panamera)Water pump leak or failure on the V8Coolant residue next to the pump or drips between the engine and the gearbox; YOUCANIC describes this for the Panamera.
Source for the symptom in the Porsche V8 and V6 (Cayenne and Panamera)^[38]
- Medium severityOccasionalFrequency: OccasionalRover K-SeriesCoolant leaks: expansion tank cap, rear block rail and hosesExpansion tank that empties quickly or traces of coolant under the car.
Source for the symptom in the Rover K-Series^[39]
- Medium severityOccasionalFrequency: Occasional1.4, 1.6 and 1.8 VVT-iWater pump leak or premature failureStains or a puddle of coolant under the engine, and the expansion tank needs topping up more often than normal.Appears at around 50,000 km
Source for the symptom in the 1.4, 1.6 and 1.8 VVT-i^[40]
- Medium severityOccasionalFrequency: Occasional1.6 Dual VVT-iWater pump leakStains or a puddle of coolant under the engine, and the expansion tank has to be topped up more often than normal.Appears at around 90,000 km
Source for the symptom in the 1.6 Dual VVT-i^[41]
- Medium severityOccasionalFrequency: OccasionalDrive-E gasolinaLeak from the expansion tank or faulty cap in the cooling systemStains or drips of coolant under the car, or an expansion tank that empties sooner than normal.Appears at around 17,900 km
Source for the symptom in the Drive-E gasolina^[42]

Which cars it appears in

These faults affect 28 engines. We have documented 202 models from 23 makes with some of the affected versions: open yours to see all its faults.

Engines

Cars with the affected versions

Audi

See all Audi models

BMW

See all BMW models

Citroën

Cupra

Dacia

DS

Ford

Infiniti

Infiniti Q30Engine: OM651Years: 2015–2019

Lotus

Mercedes-Benz

See all Mercedes-Benz models

MG

MINI

Opel

See all Opel models

Peugeot

See all Peugeot models

Renault

Rover

Seat

See all Seat models

Škoda

See all Škoda models

Smart

Subaru

Coolant leak: causes in your car

76 cars have several documented faults that cause this symptom. Choose yours to see only those that affect it, by engine and by year.

Audi 17

BMW 14

Citroën 2

Cupra 2

DS 1

DS DS 3

Mercedes-Benz 1

Mercedes-Benz Clase C W204

MINI 1

MINI Cooper R56

Opel 7

Peugeot 4

Seat 5

Škoda 7

Toyota 1

Toyota GR Supra A90

Volkswagen 11

Volvo 3

Coolant leak by brand

Other symptoms: leaks

All symptoms

Has this happened to you? Tell us which fault it was, at how many kilometres and how much you paid: it helps other owners know what to expect. Report your fault.

Sources

Every fact on this page links to its source. If you find an error, let us know.

1.Fallo del depósito de expansión del BMW Serie 5 E39Euro Premium Parts · Technical documentation · consulted 5 October 2026 · in another language
2.Porsche Cayenne I 9PA - Probleme und KrankheitenGebrauchtwagenberater · Motoring press · consulted 9 October 2026 · in German
3.Porsche Cayenne Coolant Pipe Failure: Causes, Symptoms, and Repair CostsForeign Automotive (taller de Ontario, Canadá) · Other source · consulted 9 October 2026
4.Cayenne V8 2003 to 2007 (1st gen) - Coolant Pipe Failure911UK (foro) · Owners' forum · published 18 March 2012 · consulted 9 October 2026
5.Liste des moteurs qui ont des soucis de refroidissementFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
6.Fiabilité des 0.9 TCeFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
7.Fiabilité Audi A6 (2011-2018) (106 témoignages)Fiches-auto.fr · Owners' forum · consulted 9 October 2026 · in French
8.Tous les problèmes sur Audi Q5 2008-2017 (322 témoignages)Fiches-auto.fr · Owners' forum · consulted 9 October 2026 · in French
9.BMW-Rückruf: 720.796 Fahrzeuge in den USA betroffen (Wasserpumpe)Auto Motor und Sport · Motoring press · published 21 August 2024 · consulted 27 September 2026 · in German
10.Fiabilité et pannes Ford Mondeo 3Fiches-auto.fr · Other source · consulted 27 September 2026 · in French
11.Avis Range Rover Evoque 2.2 SD4 190 ch automática, 150.000 km, de 2012Fiches-auto · Owners' forum · consulted 5 October 2026 · in French
12.Why Subaru's Head Gaskets Became A Running Joke (And Whether It's Still Deserved)SlashGear · General press · published 13 September 2025 · consulted 9 October 2026
13.Common 2AZ-FE Engine Problems and How to Fix ThemThe Auto Insider Blog · Other source · consulted 5 October 2026
14.Self Study Program 820333: The 1.4L EA211 Gasoline EngineVolkswagen Group of America (Volkswagen Academy) · Manufacturer · published February 2014 · consulted 26 September 2026
15.Golf 7 1.4 TSI: common faults and tipsAuto Gas Gaga (taller, Banja Luka) · Other source · published 6 June 2026 · consulted 26 September 2026
16.Fiabilité du Volkswagen Touran 2 : la maxi-fiche occasion de CaradisiacCaradisiac · Motoring press · published 3 May 2018 · consulted 26 September 2026 · in French
17.Mercedes OM651: Typische Probleme und HaltbarkeitGebrauchtwagenberater · Motoring press · consulted 26 September 2026 · in German
18.Bomba de agua del coche, qué es, función y cuándo cambiarlaAutopista.es · Motoring press · published 10 June 2026 · consulted 26 September 2026 · in Spanish
19.Fiabilité Bmw Serie 7 (2009-2015) (49 témoignages)Fiches-auto.fr · Owners' forum · consulted 8 October 2026 · in French
20.Fiabilité Bmw Serie 5 (2003-2010) (410 témoignages)Fiches-auto.fr · Owners' forum · consulted 8 October 2026 · in French
21.BMW 650i: Gebrauchtwagen-TestAUTO BILD · Motoring press · published 4 December 2015 · consulted 8 October 2026 · in German
22.Opel Corsa 4 : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
23.Opel Adam : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
24.Opel Meriva 2 : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
25.Opel Zafira Tourer : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
26.Fiabilité de la marque Toyota (Aygo)Fiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
27.Fiabilité de la marque Citroën (C1)Fiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
28.Fiabilité de la marque Peugeot (107/108)Fiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
29.Del 1.9 TDI al 1.5 TSI, así es el motor que ha cambiado la historia reciente de VolkswagenMotor.es · Motoring press · published 7 June 2026 · consulted 26 September 2026 · in Spanish
30.VW EA211: Typische Probleme und HaltbarkeitGebrauchtwagenberater · Motoring press · published 26 August 2026 · consulted 26 September 2026 · in German
31.Gebrauchter Audi A6 und S6 C7 ZuverlässigkeitsleitfadenEuro Premium Parts (blog de recambista) · Other source · published 29 November 2025 · consulted 9 October 2026 · in German
32.Common Problems of Audi A6 C7 3.0 TFSI: A Comprehensive GuideEuro Auto Pro (blog de taller, Australia) · Other source · published 6 October 2024 · consulted 9 October 2026
33.The 5 Most Common BMW B58 Engine ProblemsBMW Tuning · Technical documentation · published 7 February 2020 · consulted 9 October 2026
34.Der BMW B58 Motor | Technische Daten, Probleme, Haltbarkeit & Liste der FahrzeugeCarWiki.de · Technical documentation · consulted 9 October 2026 · in German
35.BMW B58 EngineFCP Euro · Technical documentation · consulted 9 October 2026
36.Fiabilité 220 CDIFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
37.Fiabilité Opel Insignia (A): pannes et témoignagesFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
38.970 Porsche Panamera Common ProblemsYOUCANIC · Other source · published 6 November 2024 · consulted 9 October 2026
39.Cooling and heating (K-Series: ZR, ZS, ZT, MGF, TF)MGOC Spares · Technical documentation · consulted 8 October 2026
40.Toyota Corolla Verso (2004-2009) : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
41.Toyota Auris (2007-2012) : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
42.Fiabilité et pannes Volvo V40Fiches-auto.fr · Other source · consulted 27 September 2026 · in French