One of our customers, Ardit Saiti, ran a test we'd been meaning to do ourselves: six back-to-back pulls on his tuned 2019 E63 S, three with the stock cooling layout and three with our E63 M177.2 Transmission Split Cooling kit installed. Same road, same gears, same procedure, and he logged intake air temperature the whole way.
Short version: stock, the peak IAT rise over ambient climbed from +18°C to +22°C across three pulls with no cooldown. With the transmission oil divorced from the intercooler loop, it ran +12°C to +14°C. That's a 36% reduction in average peak rise, and the split-cooling session was run on the hotter day. Full data below.
The problem Mercedes built in
On the M177, one low-temperature coolant loop does two jobs. It feeds the water-to-air intercoolers on top of the engine, and it also runs through the transmission oil heat exchanger. On a cold start that's convenient: the coolant warms the gearbox oil quickly. Under load it's the opposite. Transmission oil runs well above the temperature you want your charge air to be, so every time the exchanger dumps heat into that loop, the intercoolers are being asked to cool intake air with warm water.
The loop has limited thermal mass. A few hard pulls and the whole circuit heat-soaks. IATs climb, the ECU pulls timing, and the car feels slower on the third pull than it did on the first. Most owners blame the intercoolers. The intercoolers are fine. They're just sharing a radiator with a gearbox.
How it was tested
- 2019 Mercedes-AMG E63 S (W213), ECU/TCU/CPC tune, catless downpipes, otherwise stock
- 10-minute highway cruise to warm up, then three consecutive pulls with no cooldown between them
- Each pull from 3rd gear at 4,000 rpm through to 5th gear at 7,000 rpm
- Ambient 30°C (86°F) for the stock session, 31°C (88°F) for the split-cooling session
Back-to-back pulls with no cooldown is the point. One pull hides heat soak. Three in a row exposes it.
Intake air temperature, pull by pull
Each bar runs from the IAT at the moment the driver floored it to the peak during the pull. The ring marks the average over the pull.
| Run | Start | Avg | Peak | Peak rise over ambient |
|---|---|---|---|---|
| Stock 1 | 37°C | 43°C | 48°C | +18°C |
| Stock 2 | 38°C | 46°C | 51°C | +21°C |
| Stock 3 | 38°C | 49°C | 52°C | +22°C |
| Split 1 | 37°C | 42°C | 43°C | +12°C |
| Split 2 | 37°C | 43°C | 44°C | +13°C |
| Split 3 | 38°C | 43°C | 45°C | +14°C |
Two things stand out. First, the gap on the very first pull: with everything warmed up but nothing heat-soaked yet, the stock car was already 6°C hotter at peak. Second, the slope. Stock peaks walked up 48, 51, 52 and the average during each pull climbed 6°C. The split-cooled car's average barely moved: 42, 43, 43.
Peak rise above ambient
Every number here is IAT minus ambient for that session, so the 1°C difference between the two days is already accounted for.
Three-pull mean of the peak rise: 20.3°C (36.6°F) stock versus 13.0°C (23.4°F) with split cooling. A 7.3°C (13.2°F) reduction, or 36%. Stock climbed 4°C across the session; split cooling climbed 2°C.
Why 7°C matters
Intake air temperature is one of the inputs the M177's ECU uses to decide how much timing it can run. Hotter air means more knock risk, so the ECU retards ignition and the car makes less power. It also means less dense air per cylinder fill.
What the data shows is less about the first pull and more about the fifth or the tenth. A stock car that's 22°C over ambient after three pulls is heading somewhere worse on a track day, a canyon run, or a roll-race session. The split-cooled car is flat. That consistency is the thing you feel: the car that pulled hard on the first run still pulls hard on the last one. In Ardit's words: "The difference on a 2nd or 3rd consecutive pull is night and day, or a longer pull like grabbing multiple gears. After 1 or 2 shifts the stock cooling system is heat soaking and bringing those IATs sky high and the car starts to pull timing."
The transmission gets the same favor
Only intake temps were logged, but the trade runs both ways. The stock exchanger is a compromise for the gearbox too: it's cooling 9-speed MCT oil with coolant that's already been through the intercoolers. A dedicated bar-and-plate cooler with ambient air across it has far more headroom. Cooler oil holds its viscosity under repeated launches and shifts, which is where that clutch pack earns its keep.
One more thing he found
Pulling the front bumper for the install, Ardit found the space behind the radiators packed with leaves and dirt. It's worth checking on any M177 car, kit or no kit. The side coolers and the low-temp radiator sit low and collect everything the grille lets through. A heat-soaked loop with a clogged radiator in front of it is the worst case.
What's in the kit
The system replaces the stock oil-to-coolant exchanger path with a stand-alone transmission oil circuit. Oil leaves the transmission through our CNC billet fluid divorcer, runs through -10AN braided lines to a 575 × 140 × 42 mm bar-and-plate cooler mounted on the front crash bar, and returns. The intercooler loop is left to do one job. The horn relocates with the included brackets. Install is a bumper-off job with a detailed PDF guide; no cutting, no tuning change required.
- 1 × bar-and-plate oil cooler, 575 × 140 × 42 mm
- 1 × CNC billet fluid divorcer with -10AN fittings
- 2 × -10AN braided fluid lines
- 2 × cooler mounting brackets with hardware
- 2 × horn relocation brackets with hardware
FAQ
What cars does this fit?
W213 E63 and E63 S, and the AMG GT 63 4-door, which shares the M177.2 platform. Available in silver or black: E63 M177.2 Transmission Split Cooling.
Do I need a tune change?
No. The kit changes where the transmission oil rejects heat, not anything the ECU or TCU sees. Ardit's car was already tuned (ECU/TCU/CPC) and nothing was changed between sessions.
Will this help a stock-power car?
Yes. The heat-soak mechanism is the same at stock power: the gearbox still dumps heat into the intercooler loop, it just takes a few more pulls to show. Tuned cars and hot climates get there faster.
How hard is the install?
Front bumper off, cooler onto the crash bar, divorcer and lines in, horn relocated to the included brackets. Instructions are linked on the product page.
Test data and quotes courtesy of Ardit Saiti, 2019 E63 S, October 2026. Results on your car will vary with tune, ambient, and driving. Questions about the methodology? Get in touch.
