Depends on where the electronics are located in relation to open areas as well as heat sources. If you're on top of the header, you're going to be a lot hotter than if you were under the battery.
Proximity of exhaust pipes and catalytic converter can have a profound effect.
Apart from being close to the exhaust, many areas allow the use of filled polypropylene components which would imply a bit over 100 deg C. some areas need nylon which implies long term temperatures between 100 and 130 deg C with short term spikes not going over about 150 to 160 deg C
Nylon fails close to the exhaust which implies 160 to 200 deg C for a moderate amount of time (maybe 100 hours exposure)
Regards
pat pprimmer@acay.com.au
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For most integrated circuits the industrial temperature range is -40 to 85 degree C. And that spec is for free air. That's why most electronics is under the dash board.