Boost seems to cost random amounts?

[Chips11]

Hello!
I'm having issues trying to understand how much heat the game charges for the boost cycle. The instructions make it sound like I only need to pay 1 heat to boost:

Boost
Regardless of which gear you are in you may pay 1 Heat to boost once per turn. Boosting gives you a symbol as reminded on the player mats. Move your car accordingly,you may still be blocked.

When I use boost, it seems to warn me about a random cost:
"You already have 1 Heat(s) to pay, it will change up to 6 Heat(s).
Your currently have 6 Heat(s) in your engine"

How does it decide how many heats to pay?

Thank you!

[DerRico]

Boost always has a cost of 1 heat. (Weather may make it free for an area, though. )

When you boost it adds a card to your speed. If you are rounding a corner during that same turn that speed increase means that you have to pay more heat for that corner. That's what the game is warning you about.

[PaulB-UK]

In your example it sounds like you've already exceeded a corner speed by 1.

If you boost then you will have to pay 1 heat to boost, and 1 heat for every extra space you move forward - potentially up to 5 extra heat - bringing it up to 6 heat in total.

[arrie1987]

I thin Paul is right.
Probably 1 heat you need to pay already for a corner overshoot. Then boost (2nd heat), what could potential be a 1 - 4 speed extra, which will cost a potential 3-6 heat.
System gives you your maximum potential heat you beed to pay.