NHC MOTORS · SERVICE RECORD

BMW M340i Transmission Fluid Change: ZF Fluid, BG PXT Exchange and Temperature Check

We changed the transmission fluid in a 2020 M340i with ZF LifeguardFluid 8. Here we walk through the circulating exchange with the BG PXT machine and the temperature checks made during the work.

The M340i raised on the lift for its transmission fluid service.

2020 BMW M340i

Transmission fluid is not changed often. When it is, the fluid specification, the exchange method and the final fluid-level check all need attention. On this M340i we used ZF LifeguardFluid 8 and connected the BG PXT machine.

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We changed the transmission fluid with ZF LifeguardFluid 8

The fluid we used is ZF LifeguardFluid 8. Automatic transmission fluid lubricates the transmission and also carries the hydraulic pressure needed to shift gears. The product has to be chosen to meet the specification required by the transmission fitted to the vehicle.

If you keep a record of the product and mileage at the last change, it helps when you and your shop decide when the next service is due.

The ZF LifeguardFluid 8 used for this change.

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We circulated the fluid through the BG PXT machine during the exchange

We connected the BG PXT machine to remove the old fluid and supply new fluid. Draining through the drain plug always leaves some fluid in the torque converter and the lines. A circulating exchange replaces old fluid with new while the fluid is flowing, so more of the total fluid gets replaced.

Throughout the work, we watched the fluid flow through the machine's clear sight window.

Fluid flowing through the machine's sight window during the exchange.

Late in the exchange, the fluid in the sight window has changed color.

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Why the fluid temperature is checked

The diagnostic scanner showed two separate readings: a fluid temperature of 42°C and an EGS temperature of 44°C. EGS is the transmission control unit. When checking the level, don't mix up these two readings; the reading to check is the fluid temperature.

Automatic transmission fluid changes volume with temperature. The level has to be set at the specified temperature and by the specified procedure. That means the job is not finished just because the machine has put the new fluid in. The 42°C in the photo is the fluid temperature we confirmed during the work.

Scanner readout: fluid temperature sensor 42°C, EGS temperature sensor 44°C.

Transmission fluid work carried out from beneath the transmission.

What we checked during the M340i transmission fluid change

Product

ZF LifeguardFluid 8

Exchange process

Fluid flow in the machine's sight window

Vehicle status

Fluid temperature 42°C / EGS temperature 44°C

After the fluid specification is confirmed and the fluid is changed, the level must be checked at the temperature conditions specified for the transmission.

Frequently asked questions

Do all BMWs use the same transmission fluid?

We choose the fluid by checking the specification for the transmission fitted to the car. This M340i received ZF LifeguardFluid 8. When you contact us, tell us the model, model year and the product used previously. That lets us confirm the right fluid faster.

How is a circulating exchange different from draining through the drain plug?

If you only drain through the drain plug, the fluid left in the torque converter and the fluid lines mixes with the new fluid. A circulating exchange drains old fluid and fills new fluid while the fluid is moving, so more of the fluid gets replaced. On this car we used the BG PXT machine.

If the fluid becomes clearer, will harsh shifting go away?

Harsh shifting needs its own diagnosis: when it happens and what causes it. We first confirm whether it is a fluid-maintenance issue or whether the controls or mechanical parts also need inspection. Then we tell you what work is needed.

If you have been putting off a transmission fluid change

We confirm the transmission fluid and exchange method that apply to your car. Please tell us the model, model year and last fluid-change date. If shifts jolt or feel delayed, mention when that happens.

We explain the work and estimate before proceeding with your consent.

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031-258-1617 · NHC Motors, Suwon · By appointment

Published 2026-09-26