X300 4.0 engine oil viscosity grade for REBUILT engine and other oils


I tried to look over whole forum but couldn’t find exact answer for my topic despite all usual stuff such as “how much oil to put” or “what oil do you usually use”.

My X300 4,0l 177kw VandenPlas just had a complete engine rebuilt and now it’s time to fill up all new oils on it.
The question is - do someone know exactly what is the best oil to put in a NEW ENGINE so to say?
The car was and will be driven in all season weather, from -30 Celsius in winter to +30 Celsius in summer.
There are very different solutions about viscosity grade - 10W-30, 15W-30, 15W-40, 10W-40, 20W/50… So I am pretty lost.

Also, the gearbox also need oil refill. But that is not rebuilt and has run about 270 000 kilometers.

You‘ll want to change the oil after run-in so don’t worry too much. If you didn’t do it yourself ask the engine builder what oil he would use and when you change it put in what the factory recommended.

I didn’t do it myself, my friend works in car service and has his own little repair place as part-time job so he did it.
But there aren’t too many of these cars in my country and especially - not with rebuilt engines.

He knows how important car is for me so even being mechanic, he asked me to find out what would be best choice for the car.
I also thought about factory recommended oil from book. And in one book I find 0W–30, 5W–30, 0W–40, 5W–40.
In other book with X300 exact picture on it says "SAE viscosity range 5W–20 and 20W–50
dependent on ambient temperature.

Assuming we are talking about the AJ16 straight 6 engine? The handbook should give temperature ranges that each oil is suitable for. If its been a complete engine rebuild new pistons reborn bearings replaced use a running oil for a short time then replace with the temperature range that suits.
From what you are saying there is a big temp difference over the year.

I used to do Mobil 1 0w40 in the winter and 15w50 in the summer.

Then I just made things easier on myself and the car and stuck to Castrol Edge 0w40 all year round.

According to Bob Is The Oil Guy website, the viscosity of the Castrol is slightly higher than the Mobil 1, so it seems to fit neatly between the two Mobil 1 oils I was using.

I can’t figure out why anyone would want that left number as low as possible. I want the oil as thin as it can be cold, and then the proper viscosity when hot. That’s what the 0w40 does.

Yes, Robin, it’s AJ16 inline-6 piston engine. Don’t have original handbook of mine but have gathered a few from other X300 and still wanted to ask forum experts for best answer.
Yes, it has been a complete engine rebuilt and yes, there is a wide range of temperature change in my country. I live in Lithuania, Europe so during winter it can really get up to minus 30 but normally it stays around minus 15. But you know, you can never be too secure

That’s what I thought - a little bit too much hassle…

Thanks, Veekay, for your suggestion on Castrol which suits all year around! I will consider this with my mechanic.
It seems that we are having same engines on both of our cars so I have faith that you are really talking from experience.

You want that when the engine leaks a bit while standing.

The oil is too thick if the engine doesn’t crank over quick enough in winter. It will slow down oil delivery to the bearings but on my old XK engine I ran 20W50 while it was -20° and did not have any problems. 0W40 should be good in all situations. For running in a cheap oil without reduced friction additives etc is best.