Interesting. I do the same but would never refer to this as thinking. Probably something more like "visualizing" or "feeling".
It works for coding or system architecture and things like that, as well. For you, when you start thinking, a narrative voice appears? Is it debating yourself?
Occasionally there is some snippet of a sentence I imagine, but it’s almost always cut off prior to finishing the sentence. If I imagine writing something, though, I’ll speak it to myself in my head.
Funnily enough, I’m a pretty weak mental visualiser too. I don’t have aphantasia but metal images are very transparent and dark.