M20B20 won't start when it's warm outside

[level5]

Hello. I've been having some starting issues with my car. Sometimes when I turn the key to start the car, it won't do anything. No crank, not even a click. I have to turn the key off and on for like 10 minutes in order to get it to crank. Luckily I've always had someone with me to help jumpstart the car.
I recently noticed a pattern with this. The problem only occurs when it's warm outside (it's spring and where I live, it's -10*C one day and +10*C the next and this only happens on the warmer days).
What could be the cause of this?

[dnguyen1963]

I would do a smoke test first to see if you have any vacuum leaks when the weather is warmer. Things expand as the temp goes up.

[tomstin]

No crank, not even a click.... Luckily I've always had someone with me to help jumpstart the car....The problem only occurs when it's warm outside

But it starts when you put the jumper cables on it? Time for the wiring diagram and a multi meter. Check the voltage at the battery, move the battery cables. Are they clean? Tight? Does the voltage change when you move them?

My guess is something is expanding when it gets warm. If it starts when you jump it, that would suggest low voltage at the battery. But I think you will need to start at the battery and work your way through the ignition switch, relays and onto the starter.

I would bet on a bad battery.

[level5]

Thanks for the answers.
Vacuum leaks shouldn't be the issue as the starter is not getting power.
The battery should be good. I'm guessing it's the ignition switch. Tried heating the area around it yesterday and that caused it to not work. The dash lights up and everything but the start function won't do anything. After it cooled down, it worked fine.