How often should fast food restaurant replace the oil used in fryers?

Based on my experience, if you use temperture below120 C, for3 hrs each day,4 days a week , then you can use for2 weeks.

Every day after reuse of oil, it needs to fully cleaned from impurities and kept in cool place.

For checking the oil, you can use a tool to determine its smoke point. In addition, you need to avoid addition of water, contact with air and with light.

we must have a systemic approach in our business so we need measuring device .... frying oil should be changed when the level of Total Polar Materials (Polar Content) is 

greater than24%. 

 If a measuring device is not available, change the oil if the fried food has an 

unusual colour or taste. 

 Always change used frying oil before it smokes or starts foaming. 

When discarding used frying oil, use steel or other appropriate container that can 

withstand high temperatures. 

It really depends on many factors, Oil brand, numbers of use and type of food, temperature, and Work load. I would say from daily up to2 weeks depending on usage.   

overoll in fast food restaurants which have and use the fryers & the hydrogenated oils 

the oils must be refinery & full clean every  3 fried cooked

every fried  itemes must have a especially frying pan and oil too

the oils can be still good to use only for  24 houres when we use

the instruction on the equipments 

because every fried  itemes had thier own fried temperture

after24 houres in hard work the oils must be change of pace