20W-50 was the most popular weight of oil 20 years ago!! But todays engines are built so much tighter that you need a lighter oil. Also the most wear that engines have happens durning warm-up so if you stay with a lighter oil then the engine will last longer.
IF you want a good that is rated for 100+F outside temps then use a 5W-50 OR 10W-50.
MERCEDES Benz Master Guild Technician (6 TIMES)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)