I was also going to ask about fuel and agree with wreker above when hot. it's the fuel temp in the tank that is critcal - not the ambient temperature. Is it 'fresh'. After about 6 months fuel is starting to break down. CAA used to require avgas to be chemically tested if storage tank not refreshed with new fuel within six months before dispensed. Are aircraft fuel tank vents clear / unblocked? Fuel filters OK?