Noises on a cold internal combustion engine in a BMW – what is the cause?
BMW driver question
I would like to ask for an opinion on the loud firing of my car. When the engine is cold, immediately after firing up I can hear a loud crunching sound for 2-3 seconds, which immediately stops. After that, everything is OK. It runs beautifully, evenly and quietly. On a warm engine it rarely happens.
The car has an original mileage of 122,000 km. The effect is comparable to firing up a diesel in a 30-degree frost. Three seconds of noisy operation and continue normally. I’m wondering if some minimal leaks in the oil circulation system are to blame, as I’ve started to get gentle leaks from under the solenoid valves, shaft sensors and from the filter base. A colleague said it could be a valve in the filter base or the timing tensioner, but I think that’s malicious advice. Greetings and please give me your opinion.
The problem was with a BMW 318i E46 with a 143 hp N42B20 engine, but it can happen with other models as well.
BMW 318i E46 | By Alexander Lindquist[CC BY-ND 2.0]
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Response from BM Cars service
Noises that last for a few seconds after firing up a gasoline engine, usually come from the timing area. A cold engine after a prolonged shutdown may not have the right amount of oil in the top end, and thus components that depend on the right amount and quality of oil to work may give off running noises.
These are primarily hydraulic valve lash compensators, Vanos adjusting units and timing chain tensioners. Modern engine oils have the right additives that cause oil to drain more slowly into the sump when the engine is stopped and the right amount of oil to remain in the upper part of the engine. For this reason, it is very important to use the right quality of oil in accordance with BMW’s recommendations and to change the oil together with the filter no later than the period indicated by the vehicle information system.
Similar symptoms with noises after starting the engine also occur with a stretched timing chain or a faulty chain tensioner.
Oil leaks from the seals under the Vanos valves and the oil filter base can be eliminated by replacing the seals.
For an accurate diagnosis, additional checks are necessary.
Vanos system in a BMW internal combustion engine by Olli1800[CC BY-SA 3.0], from Wikimedia Commons
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BMW E46 M3 CSL by Alberto Pérez Franco[CC BY-SA 4.0], from Wikimedia Commons
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