What engine oil brand and weight should be used in the 600 after the break in period? The manual says to use a 10/40. i am thinking of going to a semi or full synthetic after? Is Motul all that they say it is? or are there better brands.
How may miles you have when you say break in period?
80% of break in happens in the first 100 miles or less. (oil change recommended)
The rest 20% happens over the next 1500 miles
If you are there go all synthetic.
Semi-synthetic is a waste of money. They are 30% synthetic and 70% group II oils (conventional). The problem gets even worse since the Mobil vs Castrol lawsuit in the early 90's. Castrol used Group III oil to make Castrol "syntec". Mobil sued as this is not a synthetic oil but rather a highly purified conventional group II oil. Mobil lost the lawsuit because although not synthetic, Castrol was claiming that it meets specs of synthetics, not that it is produced through synthetic methods.
Since using group III oils is 50% cheaper, all the other oil companies started making Group III oils naming them synthetic.
As you see buying a semi synthetic today means 70% conventional oil with 30%highly purified conventional oil. Of course they love to sell you this thing, it costs them a 20 cents more than the conventional oil and you pay almost double.
Presently there is only 3-4 oils on the market that are truly synthetic oils
Motul (only the 5100 ....I think its the one that smells like bananas)
Delvac-1 (Mobil 1 for trucks)
To give you an example, even the Shell Rotella Synthetic that its loved by so many, is 87% group III and 13% truly synthetic.