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Drop in octane value in "old" petrol (petrol kept too long)?


Super7
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A friend told me if the owner doesn't drive his car too often and his car is always parked outdoor exposed to hot weather, he shouldn't pump full tank petrol because the full tank will take weeks to be used up ie the petrol left in the tank will be subject to high temperature (from hot sun) for too long and its octance value will drop. As a result, if he pushes the engine hard when the octane value drops too low, it's no good for the engine, and the engine may "piang" !!!? [sweatdrop] [sweatdrop]

 

His advice:- if the car is not driven often, just pump enough petrol each time to last say the next 3-4 weeks.

 

I am not sure what he said is correct.

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A friend told me if the owner doesn't drive his car too often and his car is always parked outdoor exposed to hot weather, he shouldn't pump full tank petrol because the full tank will take weeks to be used up ie the petrol left in the tank will be subject to high temperature (from hot sun) for too long and its octance value will drop. As a result, if he pushes the engine hard when the octane value drops too low, it's no good for the engine, and the engine may "piang" !!!? [sweatdrop] [sweatdrop]

 

His advice:- if the car is not driven often, just pump enough petrol each time to last say the next 3-4 weeks.

 

I am not sure what he said is correct.

 

RON is a measure of how smooth petrol burns. look up how it is derived. it is benchmarked against a C8 isomer.

 

Petrol is volatile. hot weather at most the lighter molecules may evaporate from the tank, but I think it is insignificant as the range is C4-C12 isomers and light molecules are very little.

higher C molecules give higher RON. higher paraffin give higher octane.

 

In fact if the tank is kept empty for prolonged periods, water condensation due to air expanding and contracting in the tank will draw in more moist air.

a full tank will keep the moisture out.

also some say the tank internal wall has paint that is better kept coated with petrol to prevent peeling. but some mechanics says now a days won't happen liao.

 

your friend very imaginative.

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Well,petrol in tank for a few weeks is o.k.,but not 3-4 months,my butt dyno,told me fresh petrol,car a bit more power.


But i did heard oil companies put the "old stock 98 petrol",mixed with 95 petrol & send to the petrol station.

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