Oil can be considered the blood of the engine; without out, the engine will die. Your car might not not go anywhere without Fuel, but without oil it will never move again.
Understanding how the engine is lubricated and what oil to use is the key to a long-lasting and healthy engine.
NOTE: When replacing oils, always fill with the car on an even level surface. Use the dipstick to avoid overfilling the engine, and always fill differentials and gearboxes to the brim.
Based on modern oil chemistry, the best oil for the E30 is a 5W-40 Synthetic.
The recommended brands are Silkolene Pro S, Millers CFS, Motul 300V, Redline and Gulf Competition. The Motul 8100 X-Cess, Gulf Formula G, Fuchs Supersyn and Mobil Synt S are good, cheaper alternatives.
If you are on a budget, a 10W-40 semi-synthetic is a good alternative, in which case Opie recommend Fuchs XTR, Millers XSS or Motul 6100.
At this time of year, it’s beneficial to use an oil that has good cold start flow properties as it will get to the parts of the engine that need it far more quickly when you turn the key. The "w" number which means winter is the key here and the lower it is the better cold start performance the oil will have. A 15w or 20w rated oil will struggle to get around the engine in very cold temps and we would strongly recommend using a 10w, 5w or 0w for better cold start performance.
The amount of oil you need depends on your engine:
- M40 for the 316 and 318i - 4.00 litres
- M20 for the 320i and 325i - 4.25 litres
- M42 for the 318iS - 4.5 litres
- M21 for the 324d and 324td - 5.5 litres
For normal, open differentials, use a 75W-90 oil, such as Silkolene Syn 5, Redline 75W-90 NS, Castrol SAF-XO or Fuchs Sintopoid. You will need approximately 0.9L for a small case differential, or 1.7 litres for the larger (medium case) diff.
For Limited-Slip differentials, use a 75W-140 specifically designed for plate-type LSDs. A normal gear oil will destroy the plates and make it work like an open diff. The recommended options are Castrol racing b373 or Syntrax limited slip (which replaces the old SAF-XJ oil)
You need an MTF for the gearbox and I would go with the Redline MTL, Amsoil MTF or Fuchs Sintofluid. The Millers EP 75w-80 is a good cheaper alternative. You will need 1.15L for the most popular gearbox, the Getrag 240, or 1.25L for the bigger Getrag 260 found on the 325i.
For automatic gearboxes use Castrol Dexron III.
The drain plug is underneath the gearbox and the filler plug is part way up the side, and both are accessed from underneath the car. Always undo the filler plug before the drain, or, if things go wrong, you may be left with an empty gearbox and no way of filling it. You can't pour oil directly into the filler, because of the restricted space around it, so something like a squeezy bottle with a plastic tube attached is required. The correct oil is commonly sold in one litre bottles like this.
Forum users often ask "does Brand X have any effect? It contains fairy dust and virgins' tears, it's supposed to make my engine last longer."
The only response to this is: Why would you need additives? The oil companies have spent millions developing their oils, and therefore know already what needs adding and what doesn't.
Stay well clear, invest the extra in a synthetic oil instead of a semi.
Frequently Asked Questions
There are a lot of confusing parts about oil, and the science as a whole has moved on incredibly since the E30 was new. To answer all your oil questions, we have an oil FAQ where you can hear the real info on oil, straight from the experts.