Models · BMW
BMW 3 Series G20/G21 buying guide
The seventh-generation 3 Series, on sale since 2019 as the G20 saloon and G21 Touring, with a facelift that made the automatic standard. Four-cylinder petrol and diesel engines make up most of the range, with six-cylinder M340i and M340d models at the top.
The versions
- Petrol: 318i, 320i and 330i (2.0 four-cylinder B48, 156PS, 184PS and 258PS); M340i xDrive (3.0 six-cylinder B58, 374PS at launch)
- Diesel: 318d and 320d (2.0 four-cylinder B47, 150PS and 190PS); 330d (3.0 six-cylinder B57, 265PS, then 286PS with mild-hybrid assistance from 2020); M340d xDrive (B57, 340PS)
- G20 saloon and G21 Touring; rear-wheel drive, with xDrive four-wheel drive on the M340i, M340d and some others
- 8-speed ZF automatic on most cars; a 6-speed manual was offered on the 318d and 320d until the 2022 facelift
- Plug-in hybrid 320e and 330e versions were also sold but aren't covered here
What to check on a G20 3 Series
3 model-specific things to look at when you view one. They're a starting point, not the full inspection.
Coolant level on the M340i
What to look for: With the engine cold, check the coolant expansion tank level against the marks and look for dried coolant around the cap, the tank and the thermostat area. Ask whether it has needed topping up.
Why it matters: The M340i's B58 six-cylinder is shared with the M240i, where gradual coolant loss has often been traced to the expansion tank cap and its seal, with the water pump and oil filter housing area other leak points. The level warning can be slow, so a steady level in the expansion tank is what you want to see.
Oil under the rear axle
What to look for: Look on the ground under the back wheels and at the rear differential, in the middle of the car behind the rear seats, for spots of oil or a wet casing.
Why it matters: Rear differential oil leaks are a known G20 issue. A seal replacement usually cures it, and catching it early keeps the differential healthy.
Exhaust rattle on a cold start
What to look for: Ask for the engine to be started from cold and listen at the back of the car for a rattle from the exhaust in the first minute or so.
Why it matters: Quite a few owners have reported a rattle from the exhaust on cold starts. It's a known niggle rather than an engine fault, but worth having looked at.
Also in the full guide
- The particulate filter on diesels
- iDrive, camera and audio
- Recalls
- The cold start, test drive and paperwork checks for the exact version you're viewing
The full guide to the G20 3 Series
The CrankSight guide walks you round the car on your phone at the viewing, with every check for the exact version you're looking at: what to look for, where to find it, and what anything you find is likely to cost. As you go it builds an assessment of that car, and if you view more than one, it lines them up side by side.
£29 for the model, used on as many cars as you like, delivered within 72 hours or your money back.
Other generations
BMW 3 Series E36 · BMW 3 Series E46 · BMW 3 Series E90/E91/E92/E93 · BMW 3 Series F30/F31/F34
General points for the model, last checked October 2026. Every car is different, so treat this as a guide to what to look at, not a verdict on any car. CrankSight is independent and has no connection with BMW.