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

A coolant leak usually comes from the hoses, the radiator or the water pump. You notice it from stains under the car, from having to top up the reservoir every few days or from the red temperature warning light. RACE says that with the red light on you must stop immediately and that, if you suspect a leak, the safest thing is to take the car to a garage without driving it any further.^[1][2][3]

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 29 October 202646 sources How we work

Most common causes

From most to least likely according to the sources. Under each cause, the part and the related OBD codes.

1. Hoses and pipes in the circuit
Common cause
RACE cites the hoses among the leak points, along with the radiator and the water pump. They are the pipes that carry the coolant around the whole system.^[1][4]
Faults with with the water pump
2. Radiator
Common cause
RACE includes it among the causes of leaks. The radiator, normally located at the front, and the expansion tank are part of the circuit that stores and cools the fluid.^[1][4]
3. Water pump (gasket, seal or bearing)
Common cause
HELLA lists coolant loss among the symptoms of a faulty pump, alongside noises and overheating, caused by a defective bearing or seal, misused sealants or corrosion. It warns that coolant residue at the pump's weep hole does not necessarily mean it is faulty. El Español reports a mechanic's case in which the fluid builds up between the gaskets and the pump in an area covered by the intake, so it leaves no visible stain.^[2][3]
Faults with with the water pump
4. Gaskets that dry out with heat and cold
Possible cause
El Español explains, based on the mechanic, that the pump area withstands a lot of heat and that temperature changes dry out and crack gaskets and parts, causing leaks.^[3]
Faults with with the water pump
5. Faulty head gasket
Uncommon
HELLA mentions a faulty head gasket as a cause of coolant loss at the pump and of damage to the circuit, because exhaust gases reach the cooling system. El Español adds that overheating can burn the head gasket.^[2][3]
Faults with with the head gasket
6. Corrosion from ageing coolant
Uncommon
HELLA links ageing coolant, or coolant with a lot of chlorides, together with high temperatures, to corrosion that perforates the pump's impeller, housing, seal or shaft and causes excessive loss.^[2]
Faults with with the water pump

Depending on what you notice

Coloured fluid stain under the car

RACE reminds readers that not everything that drips is coolant: in summer, water from the air conditioning is normal and harmless, and the windscreen washer reservoir can also leak if its pipes crack. Coolant is the brightly coloured fluid in the circuit.^[1][4]

You have to top up the reservoir every few days

RACE lists it as a sign of a leak, along with the red warning light and an engine temperature above about 90 degrees.^[1]

Losing coolant but there is no stain

El Español reports a case in which the leak between the gaskets and the pump sits under the intake and cannot be seen on the ground. HELLA adds that some of the fluid can escape through the pump's weep hole.^[2][3]

Sweet smell in the cabin or when stopped

None of the open sources expressly describes the sweet smell. RACE and HELLA do treat coolant loss as a cause of overheating; if it smells and the level drops, have it checked at a garage.^[1][2]

The red temperature warning light comes on

RACE says you must pull over immediately and check the coolant level, and that in the event of a leak the safest thing is to call a tow truck and take the car to a garage.^[1]

White smoke or the engine running too hot

RACE cites white smoke from the exhaust and a temperature above 90 degrees among the signs of a coolant problem, and El Español warns that overheating can warp parts, burn the head gasket or even seize the engine.^[1][3]

What to check first

With the car on level ground and the engine cold, look at the level in the expansion tank and compare it with the marks. If it drops again, there is a leak.^[1]
Identify the fluid: coolant is brightly coloured; in summer, water from the air conditioning and windscreen washer fluid are other possibilities.^[1][4]
Visually inspect the hoses, the radiator and the water pump area for dampness, dried residue or cracks.^[1][2]
Ask the garage for a pressure test of the circuit and to check the pump, the radiator, the cap and the condition of the coolant.^[2][3]
If you have to top up, use the type of coolant the manufacturer specifies and do not mix types.^[3]

Can I keep driving?

Urgency: Garage soon

This is not a fault to ignore. RACE says that with the red warning light on you must pull over immediately and check the level, and that in the event of a leak you should call a tow truck. El Español agrees on stopping the car quickly, because driving on without antifreeze can cause greater damage such as warping parts, burning the head gasket or seizing the engine. A very small leak that only needs topping up from time to time has no timeframe set by the sources; the sensible thing is to find it soon.^[1][3]

How much it costs to fix

Indicative prices published by the sources cited; they depend on the car and the garage.

Repair	Price
Water pump, according to RACE (plus labour, depending on the manufacturer)^[4]	€300 – €700
Thermostat, part only, according to RACE^[4]	€40

Documented 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 severityFrequency: 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^[5]
- High severityFrequency: 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)^[6][7][8]
- High severityFrequency: 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^[9]
- High severityFrequency: 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^[9]
- High severityFrequency: 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^[10]
- High severityFrequency: 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^[11][12]
- Critical severityFrequency: 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^[13]
- High severityFrequency: 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^[14]
- High severityFrequency: 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^[15]
- High severityFrequency: 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^[16]
- High severityFrequency: 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^[17]
- Medium severityFrequency: 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^[18][19]
- Medium severityFrequency: 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^[20]
- Medium severityFrequency: 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^[21]
- Medium severityFrequency: 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^[22]
- Medium severityFrequency: 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^[23]
- Medium severityFrequency: 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^[24][25]
- Medium severityFrequency: 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^[26][27]
- Medium severityFrequency: 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^[28][29]
- Medium severityFrequency: 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^[30][31][32]
- Medium severityFrequency: 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^[33][34]
- Medium severityFrequency: 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^[35][36]
- Medium severityFrequency: 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^[37][38]
- Medium severityFrequency: 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^[37][39]
- Medium severityFrequency: 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)^[40]
- Medium severityFrequency: 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^[41]
- Medium severityFrequency: 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)^[42]
- Medium severityFrequency: 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^[43]
- Medium severityFrequency: 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^[44]
- Medium severityFrequency: 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^[45]
- Medium severityFrequency: 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^[46]

Which cars it appears in

These faults affect 28 engines. We have documented 240 models from 27 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

Jaguar

Jaguar XF IEngine: 2.2 TD4 / SD4Years: 2011–2015

Land Rover

Lotus

Mercedes-Benz

See all Mercedes-Benz models

MG

MINI

Porsche

Renault

Rover

Seat

See all Seat models

Škoda

See all Škoda models

Smart

Subaru

Toyota

See all Toyota models

Volkswagen

See all Volkswagen models

Volvo

See all Volvo models

Coolant leak: causes in your car

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

Audi 28

BMW 33

Citroën 6

Cupra 3

Dacia 2

DS 2

Ford 8

Infiniti 2

Jaguar 1

Jaguar XF I

Land Rover 4

Lotus 2

Mercedes-Benz 16

MG 5

MINI 3

Nissan 1

Nissan Micra V

Opel 14

Peugeot 11

Porsche 4

Renault 3

Rover 4

Seat 11

Škoda 15

Smart 2

Subaru 4

Toyota 12

Volkswagen 34

Volvo 10

Coolant leak by brand

Frequently asked questions

Can you drive with a coolant leak?

RACE says no: with the red warning light on you must stop and, if you suspect a leak, call a tow truck. El Español warns that driving without antifreeze can end in greater engine damage.^[1][3]

How do I know if the fluid dripping is coolant?

It is a brightly coloured fluid. RACE reminds readers that in summer water drips from the air conditioning, which is harmless, and that windscreen washer fluid can also drip.^[1][4]

How much does it cost to fix a coolant leak?

It depends on the part. RACE puts the water pump at between €300 and €700 plus labour in Spain, depending on the manufacturer, and the thermostat at about €40; the mechanic in the El Español report talks of up to €400 for the pump. We have not found a Spanish source with the price of a hose or a radiator.^[3][4]

Why am I losing coolant without seeing a stain?

El Español reports a case with the leak under the intake, with no visible stain, and HELLA explains that the pump can let coolant escape through its weep hole without necessarily being faulty.^[2][3]

Is it safe to top up with water?

The open sources do not address this point. El Español stresses that you need to know your car's coolant type and not mix types, so the sensible approach is to follow the manufacturer's specification.^[3]

Will it pass the MOT with a coolant leak?

None of the sources consulted deals with it, so we cannot say. Check with the inspection station (the ITV in Spain).^[1]

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.

¿Por qué se calienta el coche?RACE · Motoring press · published 24 July 2023 · consulted 29 October 2026 · in Spanish
Bomba de agua defectuosa: causas, síntomas y sustitución de la bomba de refrigeranteHELLA · Technical documentation · consulted 29 October 2026 · in Spanish
Un mecánico advierte sobre si tu coche pierde refrigerante: «Tienes que cambiar la bomba y todas las juntas»El Español · General press · published 20 September 2025 · consulted 29 October 2026 · in Spanish
¿Cómo funciona el circuito de refrigeración de un coche?RACE · Motoring press · published 30 May 2023 · consulted 29 October 2026 · in Spanish
Fallo del depósito de expansión del BMW Serie 5 E39Euro Premium Parts · Technical documentation · consulted 5 October 2026 · in another language
Porsche Cayenne I 9PA - Probleme und KrankheitenGebrauchtwagenberater · Motoring press · consulted 9 October 2026 · in German
Porsche Cayenne Coolant Pipe Failure: Causes, Symptoms, and Repair CostsForeign Automotive (taller de Ontario, Canadá) · Other source · consulted 9 October 2026
Cayenne V8 2003 to 2007 (1st gen) - Coolant Pipe Failure911UK (foro) · Owners' forum · published 18 March 2012 · consulted 9 October 2026
Liste des moteurs qui ont des soucis de refroidissementFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Fiabilité des 0.9 TCeFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Fiabilité Audi A6 (2011-2018) (106 témoignages)Fiches-auto.fr · Owners' forum · consulted 9 October 2026 · in French
Tous les problèmes sur Audi Q5 2008-2017 (322 témoignages)Fiches-auto.fr · Owners' forum · consulted 9 October 2026 · in French
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
Fiabilité et pannes Ford Mondeo 3Fiches-auto.fr · Other source · consulted 27 September 2026 · in French
Avis Range Rover Evoque 2.2 SD4 190 ch automática, 150.000 km, de 2012Fiches-auto · Owners' forum · consulted 5 October 2026 · in French
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
Common 2AZ-FE Engine Problems and How to Fix ThemThe Auto Insider Blog · Other source · consulted 5 October 2026
Self Study Program 820333: The 1.4L EA211 Gasoline EngineVolkswagen Group of America (Volkswagen Academy) · Manufacturer · published February 2014 · consulted 26 September 2026
Golf 7 1.4 TSI: common faults and tipsAuto Gas Gaga (taller, Banja Luka) · Other source · published 6 June 2026 · consulted 26 September 2026
Fiabilité du Volkswagen Touran 2 : la maxi-fiche occasion de CaradisiacCaradisiac · Motoring press · published 3 May 2018 · consulted 26 September 2026 · in French
Mercedes OM651: Typische Probleme und HaltbarkeitGebrauchtwagenberater · Motoring press · consulted 26 September 2026 · in German
Bomba de agua del coche, qué es, función y cuándo cambiarlaAutopista.es · Motoring press · published 10 June 2026 · consulted 26 September 2026 · in Spanish
Fiabilité Bmw Serie 7 (2009-2015) (49 témoignages)Fiches-auto.fr · Owners' forum · consulted 8 October 2026 · in French
Fiabilité Bmw Serie 5 (2003-2010) (410 témoignages)Fiches-auto.fr · Owners' forum · consulted 8 October 2026 · in French
BMW 650i: Gebrauchtwagen-TestAUTO BILD · Motoring press · published 4 December 2015 · consulted 8 October 2026 · in German
Opel Corsa 4 : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Opel Adam : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Opel Meriva 2 : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Opel Zafira Tourer : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Fiabilité de la marque Toyota (Aygo)Fiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Fiabilité de la marque Citroën (C1)Fiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Fiabilité de la marque Peugeot (107/108)Fiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
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
VW EA211: Typische Probleme und HaltbarkeitGebrauchtwagenberater · Motoring press · published 26 August 2026 · consulted 26 September 2026 · in German
Gebrauchter Audi A6 und S6 C7 ZuverlässigkeitsleitfadenEuro Premium Parts (blog de recambista) · Other source · published 29 November 2025 · consulted 9 October 2026 · in German
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
The 5 Most Common BMW B58 Engine ProblemsBMW Tuning · Technical documentation · published 7 February 2020 · consulted 9 October 2026
Der BMW B58 Motor | Technische Daten, Probleme, Haltbarkeit & Liste der FahrzeugeCarWiki.de · Technical documentation · consulted 9 October 2026 · in German
BMW B58 EngineFCP Euro · Technical documentation · consulted 9 October 2026
Fiabilité 220 CDIFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Fiabilité Opel Insignia (A): pannes et témoignagesFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
970 Porsche Panamera Common ProblemsYOUCANIC · Other source · published 6 November 2024 · consulted 9 October 2026
Cooling and heating (K-Series: ZR, ZS, ZT, MGF, TF)MGOC Spares · Technical documentation · consulted 8 October 2026
Toyota Corolla Verso (2004-2009) : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Toyota Auris (2007-2012) : fiabilité, pannes et rappelsFiches-auto.fr · Motoring press · consulted 27 September 2026 · in French
Fiabilité et pannes Volvo V40Fiches-auto.fr · Other source · consulted 27 September 2026 · in French