Massive Oil leak/blowing serpentine belts
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Newbie
Joined: Sep 2023
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E300, GLS450
Massive Oil leak/blowing serpentine belts
Hi. New here looking for help. 2017 E300. Blew serpentine belt and oil was everywhere. Cleaned all the oil, installed new belt. Idled for about an hour, all good no leaks. Went for short test drive, as soon as I accelerated and put a load on the motor, heard what sounded like a belt slap plastic a couple times then immediately stop. Pulled over, oil pouring out everywhere. Belt was still good. Drove it the mile home and just as I was pulling in the driveway, belt disenigrated. Any ideas?
MBWorld Fanatic!
Joined: Nov 2015
Posts: 1,193
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From: Oklahoma
2016 C300 4Matic traded in for a 2022 E450 Coupe
Hi. New here looking for help. 2017 E300. Blew serpentine belt and oil was everywhere. Cleaned all the oil, installed new belt. Idled for about an hour, all good no leaks. Went for short test drive, as soon as I accelerated and put a load on the motor, heard what sounded like a belt slap plastic a couple times then immediately stop. Pulled over, oil pouring out everywhere. Belt was still good. Drove it the mile home and just as I was pulling in the driveway, belt disenigrated. Any ideas?
Senior Member
Joined: Feb 2009
Posts: 280
Likes: 8
From: Sarasota FL
2020 E450 Wagon
What's the mileage on your E300?
Chicken and egg thing here. Did the belt die of natural causes (and/or lack of maintenance) and then cause the oil leak. Or did a catastrophic failure of a seal or oil line cause the belt to fail. You are going to have to find where the oil is coming from. Recommend you have a good look at the front crank seal.
This is only one possibility, but we have seen more than one N20 BMW 4 cyl engine lose a belt due to a belt tensioner/pulley issue. At which point part of the drive belt wraps around the front pulley and is forced between the pulley & front cover. The belt then finds it's way past the front crankshaft seal, entering the crankcase. If you have ended up with a failed front crank seal due to the belt failure, the oil pan will have to be pulled to remove all the belt debris. The rotating timing chain chops up the belt into pieces. A good part of that will end up in the oil pump pickup, potentially causing engine failure.
Chicken and egg thing here. Did the belt die of natural causes (and/or lack of maintenance) and then cause the oil leak. Or did a catastrophic failure of a seal or oil line cause the belt to fail. You are going to have to find where the oil is coming from. Recommend you have a good look at the front crank seal.
This is only one possibility, but we have seen more than one N20 BMW 4 cyl engine lose a belt due to a belt tensioner/pulley issue. At which point part of the drive belt wraps around the front pulley and is forced between the pulley & front cover. The belt then finds it's way past the front crankshaft seal, entering the crankcase. If you have ended up with a failed front crank seal due to the belt failure, the oil pan will have to be pulled to remove all the belt debris. The rotating timing chain chops up the belt into pieces. A good part of that will end up in the oil pump pickup, potentially causing engine failure.
Last edited by GermanCars; Oct 5, 2023 at 02:49 PM.
