Suggested

Engine System Rework?

Yes, full support. Having a fixed number of engines, 6 per car perhaps, during the season could really add some quite nice extra layer of strategic managing to the game. Using fresh engines for the first races but having only used ones for the remaining races, using fresh engines for the races the team might be best in or trying to keep as many fresh engines as possible for the last races when the cars are about equal due to the design cap and so on.

As a bonus Cooling would have some use.
The number of spare engines would be fixed too, 1 or 2 spare would be enough. The penalty for using an extra engine doesn't have to be a starting grid, although having to start from the pits would hurt. Agreed, even starting dead last from normal grid would not be much of a penalty, I'd use races where using hards for first stint works for that. A money fine would indeed be meaningless, since it can be printed from tokens, unless it'd be a really high fine but that sort of would allow to buy success with real money.

Still, there're a lot of penalties to choose from that can work, like a time penalty, like 10 seconds for 50% races, added to the race finish time or a penalty pit stop.

We already have a token penalty for extra engines, if you're in a two car league and want to change both car's engines every race it's going to cost you on average 1 token per race. When you reach higher manager levels (so you're not constantly chasing new staff and upgrading facilities) you can just about get away with changing engines every race if you carefully manage your sponsor tokens and cash.
If the penalty is increased to 3 tokens per engines as suggested by Rory, yes it will result in many managers changing their behaviour and running their engines for more races, but it also turns iGP into a "pay to win" game. Some managers will buy tokens with real money and use them to renew engines every race.
A better solution would be to make it so you get ten engines every 20 races but remove altogether the option to purchase extra engines.

It seems you assume someone suggesting an ingame mechanic mirroring a real life F1 rule must also share the same reasons and intentions. Which is not the case. The option for limiting engines, at least my support of it, has nothing to do with money or token budget reasons of any kind in iGP. It's meant to be an option for leagues to enable an extra layer of strategic planning of when to use fresh engines to enabe the full performance of the car and when to go for the unavoidable handicap of running with used engines.

You're right, though, that managers would use extra engines unless the penalty is such severe that enabling extra engines at all wouldn't make much sense in the first place. It's better to make those extra engines available penaltyless but for tokens, which also addresses the problem that we can't just remove engines for tokens without a replacement. So maybe 6 engines standard per car, enough with engines lasting 3 races, 4 with good Cooling stats. Then 2 extras usable at most per car buyable for token and with 1 for 6 token, 2 for 5 token and 4 for 16 or 17 token it should about match the token expenses of the current system. In competetive leagues it means using all extras, like it is a fresh engine every race without engine limits.

As said I am not aware of any problem with the current system and, as said, not meant to be any kind of solution for one from my side. It's meant to be an expansion of the game.

The price for engines in the current system is very well balanced in the current system in my opinion. As Kevin already wrote rising those costs significantly would force manager to buy tokens to be able to use a new one each race which means a pay2win system.

Double posted somehow.