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Diesel engines require glow plugs to pre-heat the combustion chambers before starting in cold weather. If one or more glow plugs have failed, the engine will struggle to start in temperatures below 5°C. Testing the glow plugs with a multimeter (0.5-2 ohms per plug is normal) identifies failed units. Replace plugs in sets where possible. Also check the glow plug timer relay which controls the pre-heat duration.
Based on 468 driver confirmations
New glow plugs made no difference. Compression test showed number 3 cylinder was down to 240psi, rest were 380+. Worn injector was allowing fuel to wash the bore. New injector and a compression recovery treatment improved it enough to start reliably. Not a cheap fix but better than a new engine.
Parts replaced: Diesel injector (cylinder 3), compression treatment
Plugs tested fine individually. Found the relay wasn't energising them — no power reaching the plugs on cold start. New relay was £14. Fitted in 5 minutes. Cold starting is now perfect. Check the relay before changing the plugs — much cheaper.
Parts replaced: Glow plug relay
Diesel would crank for ages in cold weather before catching. Sometimes wouldn't start at all below 3 degrees. Tested each glow plug — two were open circuit, completely dead. Replaced all four at the same time since the others were original at 120k. Starts instantly now even at -5. Should've done it years ago.
Parts replaced: 4x glow plugs
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