Which engine oil should I use for an LPG conversion?
I am unsure of what engine oil to use for my 1999 BMW 316i compact. It has a 1.9 engine converted to LPG and has done 189,000 miles. Haynes manual says 15W 40. The online 'tap in your reg' section give varying specs, mostly 5W/30 or 5W/40. This is where it gets confusing because the car has high mileage but is in very good order and drives really well in my opinion.
Well the grading of oils is as such, 5W/20. The first number refers to the viscosity of the oil, the lower the number the thinner the oil. The W refers to the winter grade. The second number refers to the viscosity of the oil when at 212 degrees Fahrenheit. Thinner oil makes for easier running and thus better fuel consumption. Higher viscosity means less chance of wear. The oil recommended for your engine (non LPG) for up to 10C is 5W/30. It really is your choice as to what protection you want because of wear versus fuel consumption. Given the age of the engine we would suggest that protection would be the main concern and as such use something like Castrol GTX Modern Engine at 10W/30.
Answered by Alan Ross on