So this problem is impossible to show, but easy to explain.

I fill a combustion engine with fuel, and then power it with a lever after attaching a wooden kinisis pipe to it, and It runs without a problem.

I then turn the engine off, and then flip the switch again, and the engine will not run.

The bug: It seems as though combustion engines can only be powered once.

There is a cooldown period after stopping an engine.

this is indeed not a bug. If you turn off a combustion engine it will cool down and then wait a bit before turning back on

Maybe a little tooltips ?

Can you consider reopening this bug?

I was very confused as to why my engines weren't running, and through trial-and-error discovered that they'd start back up after a short delay once then reached 20°C. It took me a good hour or two to figure it out though, and my Google-ing found some other bugs closed as "can't reproduce", but mostly said "engine won't start" — I wonder if this wasn't what they were hitting.

Some sort of visual feedback of "engine is in cooldown mode" would be great.

Addressed in 48daafa

@CovertJaguar has some plans to address this I believe

He wanted for a visual hint that the engine is cooling. That commit just made it cool down faster.

From what I understand the fixed cooling penalty has been removed. Now as soon as the temperature stops dropping the engine can start again. Previously there was an additional cooldown that wasn't really indicated anywhere

Removed? I though it was just lowered from 30 seconds to 10.

My bad it was lowered down to 10 ticks not 10 seconds.

Lowered from 30 seconds to 10 ticks

I'd have removed it entirely, but that was too much work since the state machine was using that as state information. ;)