Short answer: the S55 does not run out of power because it runs out of turbo. It runs out of cooling. On a warm day, after two or three hard pulls, intake air temperatures climb, the ECU pulls timing to protect the engine, and the car feels flat. The fix is more cooling capacity at the front of the car — and on a standard S55 the charge cooler radiator is the single most effective upgrade.
This applies to the F80 M3, the F82 and F83 M4, and the F87 M2 Competition, all of which run the same 3.0 twin-turbo straight-six.
How the S55 cools its intake air
Most turbocharged cars use an air-to-air intercooler: a radiator in the bumper, boost air passing through it, outside air passing over it. The S55 does it differently. It uses a water-to-air charge cooler, mounted in the intake manifold, fed by its own low-temperature coolant loop with a radiator at the front of the car and its own pump.
The advantage is response. The charge cooler sits right on top of the engine, so there is very little pipework between it and the inlet valves, and the car builds boost instantly. The disadvantage is capacity. That low-temperature loop holds a modest amount of coolant, and the radiator feeding it is small.
On a road drive you will never notice. On a track day, or a series of hard pulls on a hot day, that small volume of coolant heats up faster than the radiator can shed it. The coolant gets warm, so the charge cooler stops cooling, so intake temperatures rise, so the ECU pulls timing. Power drops and stays dropped until the car cools down.
Enthusiasts call it heat soak. It is not a fault — it is the standard system reaching its limit.
What actually fixes it, in order
1. Charge cooler radiator — the biggest single gain
A larger front-mounted radiator for the low-temperature circuit gives the system far more capacity to dump heat. This is the upgrade that keeps intake temperatures stable through repeated pulls rather than climbing with each one. If you do one thing to an S55, do this.
- Charge cooler radiator kit — M3 F80 (S55) 2014–2018 — £324.49
- Charge cooler radiator kit — M4 F82 and F83 2014–2020 — £324.49
- Charge cooler radiator kit — M2 F87 (S55) 2018–2021 — £324.49
2. Oil cooler — for sustained hard use
Intake temperature is the thing that costs you power on the next pull. Oil temperature is the thing that costs you an engine over a season. The S55 runs its oil hot under sustained load, and oil that spends its life above about 130°C degrades far faster than oil that does not.
If the car only ever sees road use and the occasional spirited drive, the standard oil cooling is adequate. If you do track days, or sustained high-speed running, an uprated front oil cooler is cheap insurance against a very expensive problem.
- Front oil cooler kit — M3 F80 (S55) 2014–2018 — £214.49
- Front oil cooler kit — M4 F82 and F83 2014–2020 — £214.49
- Front oil cooler — E90 and E92 M3 (S65 V8) 2007–2013 — £356.94
That last one is worth a note: the naturally aspirated S65 V8 in the E90 and E92 M3 has no charge cooling to worry about, but it is well known for running hot oil on track. For those cars, the oil cooler is the upgrade.
3. Everything else
Downpipes, intakes and a remap all add power, and they all add heat. Doing them before you have sorted cooling means the car makes more power for a shorter time before it pulls timing. Cooling first, power second — it is the less exciting order, but it is the one that gives you a car that is still quick on lap three.
Does this apply to the diesels too?
Different problem, same principle. BMW's six-cylinder diesels use a conventional air-to-air intercooler and suffer their own version of heat soak, particularly when remapped. We covered that separately in BMW diesel cooling: when an intercooler or oil cooler is worth it, and we stock front mount intercooler cores for the G30 and G31 5 Series, G32 6 Series, G11 and G12 7 Series and G14, G15 and G16 8 Series.
Common questions
Will a charge cooler radiator add power?
Not on a single cold pull — peak figures on a dyno from cold barely move. What it adds is consistency. The second, third and fourth pull stay close to the first instead of dropping away.
How hot is too hot on an S55?
Intake air temperature is the number to watch. Rising steadily through a session, with timing being pulled, means the charge cooling has run out of capacity. Logging it is the only way to know for certain what your car is doing.
Do I need to remove the bumper to fit these?
Yes, for front-mounted radiators and oil coolers the front bumper comes off. It is a straightforward job on these cars but it is not a ten-minute one. Budget a morning, or have a garage do it.
Is this worth doing on a standard car?
If you track it, yes. If it is a road car that occasionally gets used hard, the charge cooler radiator is still worthwhile and the oil cooler is optional. If it is a remapped car that gets tracked, both are close to essential.
What about the crank hub?
Not a cooling issue, but worth knowing about if you are running a tuned S55 — it is a well-documented concern on high-power examples and is a separate job entirely. Cooling upgrades do not affect it either way.
Not sure which kit fits your car? Send the make and model and we will confirm it before you order. sales@omiwheels.com or WhatsApp +44 7753 828059. Next day dispatch, free UK and Ireland delivery on OEM style wheels, and no import charges into the EU.