Solved

Engine restock question

If I have say, 4 engines left at the restock deadline, will I be restocked with 6 new engines to make a total of 10 or will I get 10 new engines taking my total to 14? I suppose I'm asking if I can accumulate a bank of engines or is the maximum always 10 at any one time?

Maximum 10 engines per car. If you have 4 engines left you will receive just 6 more

If you have less than ten engines, you will get enough engines so that you have 10 again.
If you have more than 10 engines, you will get exactly zero engines.

As the above two replies, the engine supplier only tops you off to 10 engines. (20 for 2-car leagues)