What is thicker 5W40 or 20W40

Motor oil: myths and fairy tales


Quote: “The 0W40 runs out everywhere! Better take 10W40, it's thicker! This reduces oil consumption and oil loss! "

You read / hear such or similar looks almost every day, even from workshop employees or "masters"! And it is really amazing how such false statements hold up in today's information age.

Let's see what the numbers before and after the "W" mean. A 0W40 is not a bit "thinner" than a 5W40, 10W40, 15W40 or 20W40 at operating temperature because they all have the same viscosity index of 40 when hot.

Only at low temperatures (oil = cold) does a 0Wxx have a lower viscosity than 5W40, 10W40, 15W40 or 20W40. The viscosity of a 0Wxx at, for example, 0 ° C or 40 ° C is still by a factor of 2 to 3 (!) higher (Oil = THICKER!) Than at operating temperature because the oil becomes considerably THINNER when it is heated than it is when it is cold.

So there is no oil that is too thin when cold and can cause engine rattling, burns or the engine leaks if the seals and the entire engine can cope with the much lower viscosity at operating temperature where the oil is significantly thinner. As a result, when the engine is cold, the 0W40 oil is still much too "thick" or has too high a viscosity compared to the viscosity of the oil when it is 90 degrees hot.

Of course, at operating temperature, there are oils that are even thicker than xW40, e.g. xW50 or xW60. If you drive a vehicle whose engine, for whatever reason, has a permanent oil temperature of 130 - 150 degrees, an xW50 or xW60 is safely attached. Thanks to the oil / water heat exchanger, the diesel hardly ever exceeds 100 degrees in everyday life, so an xW40 is completely sufficient and ok here. Also with regard to a possible oil dilution due to the entry of diesel (DPF regeneration) you already have significantly more reserves with an oil of 40 than with the xW30 filled in at the factory.

Oil consumption

If you drive an xW30, it is thinner than a 40 oil at operating temperature. Accordingly, it MAY happen that the engine burns it more easily because the thinner oil can cheat better past e.g. piston rings. It is not only due to the viscosity of the oil itself, but also to which additives are in it.

Castrol oil, for example, is very, let's call it, "easy to burn", especially as longlife. There it is even desired that some of it burns so that one or the other liter has to be refilled within the 30 tkm in order to add fresh additives to the total oil. This is the only way for the oil to survive the 30 tkm.

The best oils for combustion resistance are Mobil 1 oils ESP 0W40, New Life 0W40 / FS 0W40, Peak Life 5W50 / FS x1 5W50.

Here is my experience with the Mobil 1 oils from my own fleet:

- Honda Prelude 2.2 VTEC: with Castrol 5W40 1 liter over 1000 km, with Mobil 1 5W50 1 liter over 5000 km

- Audi 200 20V Turbo Quattro: with Aral 5W40 1 liter over 1500 km, with Mobil 1 5W50 1 liter over 8000 km

- Opel Kadett Turbo: with Castrol RS 10W60 1 liter on ~ 2000 km (and oil sludge!), With Mobil 1 5W50 1 liter on 10000 km (!)

- Opel Calibra Turbo: Oil consumption with Shell 5W40 1 liter for ~ 1000 km, with Mobil 1 5W50 1 liter for ~ 6000 km

- BMW 323ti: with Agip 5W30 1 liter for 1000 km, with Mobil 1 0W40 1 liter for ~ 5000 km

- Omega B 2.2 DTI: with GM Dexxos2 1 liter over 3000 km, with Mobil 1 0W40 1 liter over approx. 8000 km

- Omega B 2.5 DTI: with GM Dexxos2 1 liter over 3000 km, with Mobil 1 5W50 1 liter over 8000 km, also with Mobil 1 0W40

- Omega B 3.0 DTI: with Mobil 1 0W40 no oil consumption over 6000 km, with Mobil 1 5W50 no oil consumption over 10,000 km

- Honda Civic Coupe 1.6i: with Agip 5W30 1 liter over 1000 km, with Mobil 1 0W40 1 liter over 4000 km

- Honda Civic IX 1.8 i-VTEC: with factory filling (presumably 5W30) 1 liter over 6000 km, with Mobil 1 0W40 approx. 0.5 liter over 10000 km

Everyone has their own experiences and I have been meticulously documenting all of my oil consumption since 2000. The two Mobil 1 oils (NewLife 0W40 / PeakLife 5W50) significantly reduced the oil consumption of EVERY car (the above list is incomplete), sometimes almost to 0 within an interval. I have already given some vehicles, including those of friends and acquaintances, the oil drunkenness.

This is due, among other things, to the additional additives that swell old seals and make them soft again so that valve stem, valve cover or oil pan seals, among other things, can become tight again. Of course, the whole thing only helps if the previous oil is no good and not if there is really a defect.

Apart from that, my route consists of 90% motorway and a lot of full load, i.e. the engines are driven tight, even at the upper speeds. Hence the comparatively high oil consumption. Such an M57 takes at a constant 4900 rpm. then already a sip or two.

For example, my brother's Omega B 2.2 DTI (Mobil 1 0W40) doesn't need any oil at all, but it only drives in the city and a lot of long distances at 120 km / h (a good 40 tkm per year). If he visits me e.g. and lets it fly the 450 km, he also takes a little bit. It is completely normal to the extent that an engine consumes some oil when driving long full-load stretches at higher speeds, even a 911 Turbo or GT3 takes a sip or two in this scenario. Piston rings do not seal 100%.

Dependence of the engine acoustics on the oil viscosity

A thicker oil naturally has a better damping behavior than a thinner one. With 0W20 an engine will "rattle" a little more compared to thicker oil (when it is warm). With 40s it gets a lot better and with 50s he would be even calmer.

I have also tested this myself on the 2.5 liter M57 because before changing from 5W30 to 0W40 I first drove the 5W50 for about 8000 km in between to clean the engine (the oil is one of the best) and only then to 0W40 changed.

The 5W50 is actually too thick at the oil temperatures usual for diesel. You can drive it without any problems, it makes little sense with normal everyday use because a little more power is lost for pumping (thicker) oil and you otherwise have no real advantages. I drive the 5W50 in the 3 liter M57, but this is not driven in everyday life and therefore gets "fire" more often in percentage terms. I simply allow myself the additional security provided by the more shear-stable oil.

There are also people who still fill in a 10W40 oil. Why they do this is beyond my logic, as there are much better 5W40 or 0W40 oils today. Unless you want the oil to reach all lubricating parts only slowly during a cold start and the wear is as high as possible, especially in winter. Then always in with it. :)