Q: Will it hurt my motor to switch from synthetic oil to conventional oil?

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Will it hurt my motor to switch from synthetic oil to conventional oil. The mechanic who replaced my main seal said it wouldn't hurt but now my car smokes at cranking and slow idle it had no problems prior to the seal replacement

My car has 200000 miles.
My car has an automatic transmission.

Hi there. There are varied opinions about switching from synthetic oil to conventional oil. I am old school and believe you stick with the manufacturer’s recommendation for oil type. Nowadays, most conventional oils are a synthetic-blend. I believe BMW recommends synthetic oil.

Given your vehicle has 200,000 miles, it could be the engine’s oil consumption is somewhat normal. Replacing the rear main seal or switching oil type should not have caused the engine to start smoking.

If the smoke is black, it could be excessive fuel consumption. If the smoke is white with a bluish tint, it could be oil smoke. If the smoke is white and dissipates quickly, it could be condensation (cold) or coolant/antifreeze (warm). Switching back to synthetic oil may or may not help. If you would like to have another technician give the vehicle a second opinion, a certified professional from YourMechanic can come to your car’s location to inspect the smoking and idling problems so that this is properly resolved.

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