BMW M2: S55 cooling system on the Competition — water pump and thermostat

The M2 Competition swapped the earlier car's N55 for the S55 twin-turbo used in the M3 and M4, and it inherited that engine's cooling weaknesses along with its performance. The mechanical water pump wears under the thermal load, and thermostat failure stops coolant circulating properly, at which point overheating at full load can develop within minutes rather than gradually. The short timescale is the point: on this engine there may be very little between the first warning and real damage, and it tends to show itself during exactly the kind of driving an M2 is bought for. Worth checking carefully on any car that has seen track use, and worth paying a little more for one with a documented cooling service.

• Temperature climbing quickly under sustained load rather than settling
• Coolant level dropping, or coolant warning messages
• Engine slow to warm up, or the heater blowing cool
• Coolant smell, steam, or dried residue around the front of the engine
• Reduced-power mode after a hard drive

1. 1

   Start with the cold checks, before the engine is run.

2. 2

   Check the coolant level in the expansion tank against its marks and look at the coolant itself — clean and coloured, not murky or oily.

3. 3

   Look across the front of the engine for dried coolant residue, which appears as a crusty coloured deposit rather than a wet patch, and check the ground where the car normally sits for coloured drips.

4. 4

   Then watch how the temperature behaves rather than just glancing at the gauge: from cold, note how long it takes to reach normal operating temperature, because a thermostat stuck open makes it slow and leaves the heater blowing cool.

5. 5

   Once fully warm, give it some sustained load — a firm run up a hill — and watch the temperature reading throughout for anything that climbs instead of holding, and check afterwards for any reduced-power message.

6. 6

   Listen at idle with the bonnet up for a whine or rumble from the water pump.

7. 7

   Ask when the pump and thermostat were last done and ask for the invoice, and ask directly whether the car has been tracked.

8. 8

   If a workshop inspection is possible: have the cooling system pressure-tested and the stored temperature faults read.

Parts involved: Water pump, Thermostat.

$1,200 to $4,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “When were the water pump and thermostat last replaced?”
• “Has the car ever overheated or gone into reduced power after a hard drive?”
• “Has this car ever been used on a track, and how often?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.