Currently, engines are supplied every 20 races. Most managers replace the engine every race to avoid performance loss. Since there aren't enough engines, we always need to buy more from the store with tokens, which helps the game financially.
My suggestion is to create another, more restrictive option for Leagues. There would be a fixed supply of engines each season, to be decided by the league administrator. Instead of having to buy engines when they run out, we would pay for them when the season starts.
The options could be 5, 7, or 9 engines per season, with the same price—15 tokens, for example. That's up to you.
This suggestion would give greater importance to the Cooling attribute and wouldn't affect the game's revenue, as we would continue to purchase engines with Tokens.