Why does my Mercedes 240D lose power, stall or not start?

Short answer: On a 240D, power loss, skipping and stalling almost always trace to fuel starvation: clogged main and prefilters, an air leak in the lines or primer pump, or a clogged tank strainer or vent. One owner fixed it with both fuel filters and an air filter. A no-start is often the glow plugs.

Symptom: The diesel lugs or skips under load, stalls after running a while, or cranks but won't fire.

What to check first

1. Look at the clear prefilter. If it's dark or dirty, replace both fuel filters.
2. Replace the air filter if it's old.
3. Check every fuel line and the hand primer pump for wetness or cracks that could let air in.
4. If it stalls after a while and restarts after sitting, loosen the fuel cap to test for a blocked tank vent.
5. On a no-start, check that the glow plugs get power when you turn the key to the glow position.

Likely causes

1. Clogged fuel filters and prefilter. The 240D has a main fuel filter and a small see-through prefilter. Diesel sludge clogs them and starves the injection pump, so the engine skips and loses power.
2. Air leak in fuel lines or primer pump. Diesels can't run with air in the fuel. A cracked line, loose fitting or leaky hand primer pump lets air in and the engine stalls.
3. Clogged tank strainer or blocked tank vent. A screen in the fuel tank can clog, and a blocked vent lets vacuum build in the tank. Both starve the engine after it runs a while.
4. Glow plugs not getting power. Glow plugs heat each cylinder so a cold diesel can start. If they or their relay fail, it cranks but won't fire, especially in cold weather.
5. Dirty air filter. A choked air filter leaves the diesel short of air and it smokes and loses power.

What it usually costs

Owners didn't post prices. Filters are inexpensive and a common DIY job. Tank strainer cleaning, injection work or glow plug relay diagnosis is shop work; get a quote from a diesel or Mercedes specialist.

Is it safe to keep driving?

A diesel that loses power or stalls on the highway is a hazard. When it stalls, power brake assist fades after a few presses. Fix the fuel supply before highway driving.

DIY or shop?

Filters, air filter and glow plug checks are DIY-friendly. Tank strainer or injection pump work is better for a specialist.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA's recall lookup returned no data for the 240D model years we queried on 2026-10-28, so we couldn't confirm recalls here. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: This is an old diesel and NHTSA's online data for it is thin, so owner experience matters most here.
• NHTSA complaints: 0 keyword-matched complaints for Mercedes-Benz 240D 1974–1983 (of 0 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-28; keywords: start, stall, glow, fuel, brake, vacuum, skip, miss) (NHTSA returned no data for 20 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 1981 240D Mercedes Benz stalling on Car Talk, a 1981 240D owner said the car lost power and stalled. Replies pointed to the fuel filters, an air leak in the lines or primer pump, a clogged strainer in the tank, and a blocked tank vent.
• In 1982 240D Mercedes Benz---Skips on Car Talk, the owner of a 1982 240D that skipped and lost power reported the fix: replacing both fuel filters and the air filter. The small prefilter had turned black and was clogged.
• In 240D ran fine, now won't start... glow plugs? primer pump? starter? fuel system? on Car Talk, a 240D that had run fine stopped starting. Members said to check that the glow plugs actually get power and work through the fuel system and starter. One suggested a push start to see if it fires.
• In 1978 Mercedes 240D Brakes less responsive b/c of vacuum system? on Car Talk, a 1978 240D owner felt a weaker brake pedal with a hiss. Members explained the brakes use engine vacuum through a booster, and said to test the vacuum booster and its check valve before blaming the master cylinder.

Quick tip

With an old Mercedes diesel, change both fuel filters first. It's cheap and fixes a surprising number of 'it's dying' complaints.

Vehicle focus: Mercedes-Benz 240D diesel (W115 and W123 sedans), 1974-1983.

Safety / mechanic note

Power loss in traffic and weak brake assist are safety issues. Verify with a mechanic.