have a 2005 5AT G35 Coupe with 39K miles and very mild mods...no forced induction. this is a street car and only driven about 5K miles per year. she sits in the garage for about 4 months a year in winter attached to a Battery Tender. every spring she gets an oil/filter change and any other fluids/belts/etc. that may need to be done. use to take to a garage that specialized in G's/Z's, but they went out of business. decided to take car to my German specialist indie who works on my VW Passat daily driver. have always put Mobil 1 5w30 full synth in the G and Castrol 5w40 full synth in my Passat. I'm not one of those guys who messes around with the weights and viscosity. just go with what the factory says. just noticed after my 1st oil/filter change at my indie that Motul 8100 5w40 was on the invoice. it could be he just forgot since he works mostly with 5w40 on the German cars and just did my last Passat oil change with the Motul 8100. but if not, is this a problem? from what little I know I don't think it is, but was just looking for confirmation from an oil guy. I do take pride in keeping proper maintenance on my cars. thanks in advance for any advice.

 

well one time difference wouldn't really hurt anything changing up brands or synthetic to regular. the most important thing is the viscosity .You def. want to be running 5w30 or 5w40. You should only be concerned if they put like 15w50 in it or something. He probably doesn't stock mobil1 and that's what he had. If you like mobil1 (my preferred brand) bring your own oil next time or go somewhere else.
To sum it up. NO it will not have any catastrophic effects on your engine.

 

Thank you sir. That is what I thought, but thanks for confirming.