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Sounds normal as the coolant isn't being pushed by waterpump and is sitting on the temp sensor. Soon as you fire it up the flow is circulating again and brings it down to normal temps . It's actually scary having the digital gauge up as you reliese how much it fluctuates till it settles it self around 91/92 deg ,Funny enough ,i tightend a few hoses yesterday ,that were leaking, and went for drive, temp all good, stoped and washed the car, checked temp again, up to 99c ,started temp droped to 92 93, hot day here yesterday, temp was all good
I don't know about gas making a car that's properly tuned to run hotter maybe they do but I don't think petrol or gas would affect the cooling temps of a car if everything is good in the cooling side of thingsit will sit just under half constantly but when I run it on gas it moves up and on hot days the engine light will come on when I am using gas a mechanic told me it is because the gas runs hotter it is tripping the sensor so make it run cooler but he didn't say how to make it run cooler and that is the reason for the question thanks for your answers and your help