Thanks for your replies

I just worry about him and probably needlessly

If you want to add to his play you need to use his interests, you say he loves vehicles, try and encourage him to draw them after he has lined them up, give him large boxes he can draw on to turn them into cars, get him a racing drivers dress up kit. Its how schemas work, you have to go with them.
My ds now age 7 used to be obsessed with bin lorries and sweeping and used to get very upset at playgroup if the other children kicked the leaves around, I always thought he behaved very oddly, but he did move on eventually.Try not to worry and don't compare him to other little boys they are all very different.

I don't think you need to worry. You sound as though you're concerned that he isn't developing socially in a normal way, and I presume you're thinking ASD when you talk about him not being able to imagine being someone else. But on the other hand you feel he has learned social behaviours from the other children at nursery, and acquired new ways to express his emotions. It doesn't sound very worrying to me. He sounds like a thoughtful, confident little boy who is not a social butterfly. I know how easy it is to worry yourself into knots, but he really does sound very normal!

Lots of children use play schemas to explore and learn about their world. It can make their play seem very repetitive as they repeatedly play in similar ways, or with similar objects as if extracting every last little bit of learning before moving on to the next thing.

this article explains it much better than I can, and gives some useful examples.

I'm sure your DS is fine - just busy processing all his new experiences.

DS 3.7 is a bright and lovely little boy but some of his behaviours worry me

He is very repetitive. Repeating things over and over, wanting to watch the same TV programme or listen to the same song again and again

He does have imagination but doesn't ever really express it through drawing/painting or dressing up. This might just be his preference and that is fine but he just doesn't seem to 'get' painting or dressing up at all. It is as if he can't imagine being someone else. He also doesn't like getting his hands messy at all

He is obsessed with vehicles (very common for a little boy his age I know) and lines them up and studies every little detail about them.

He is affectionate and has formed loving relationships, although I feel he didn't really bond to me like other children do to their mothers. He never had stranger anxiety and would often push me away. If I had been at work (he stayed with his Granny) when I returned he wouldn't even make eye contact with me. He is affectionate now but when I pick him up from playgroup and he rushes up to hug me and shouts 'mummy!' I have this sense that he is just copying the other children. At his halloween party at playgroup I felt he wasn't mixing with the other children as well as the others

My MIL (who has had four children and was a nursery teacher) says I have nothing to worry about, that he might have slight obsessive compulsive traits but then don't a lot of us? My DH thinks he is fine and I am worrying about nothing. His playgroup leaders think he is fine. So why am I worried?