One would think we all know what engine oil our van requires but this time i am not sure so would appreciate your input.First thing I have a Autotrail motorhome 2.8jtb 2001. Its had 10/40 oil before but at 33000 miles I had a 36k service , when looking at the sheet i found they had put in 5/30 Gulf Synthetic. When i rang them they did say if i was not happy they would change it. Awhile later they came back and said Fiat use the 5/30 instead now. My thoughts were its to thin but as it is synthetic perhaps its ok. Over to you guys.