Miscellaneous Twinair OilChange

[HWMAX]

The viscosity of the oil has an effect on the combustion mixture and exhaust emissions. As a result there is a procedure carried out by means of the OBD2 port called "Oil Change Reset" This resets an ECU that controls the variable valve timing and variable valve lift, both of which use hydraulic tappets filled with engine oil. The flow rate of the oil in and out of these tappets is important and after an oil change that flowrate changes. The ECU reset discards the values associated with the old oil and tells the system new oil is in the system. As an automation engineer I would hazard a guess this also intiates a "learn" mode so the ECU performs measurements and calculations required to set up the required valve timing and valve lift in an accelerated process, whereas normally it would be adjusting slowly to gradual changes in viscosity. The upshot of this is that an oil change can alter engine performance and exhaust emissions in the short term. Using the wrong viscosity might have more severe consequences, I don't know, never done that. I have used the correct viscosity from other manufacturers with no problem. I also usually don't actually do the "Oil Change Reset" and have had no real problems but then I wait until after the MOT emission test before changing the oil. You may want to consider all this when deciding when to change the oil. One final point, my OBD2 scanner has a facility to do the reset but it doesn't work even though the VIN No is read by the scanner and all the valve data can be viewed live, I have to get the laptop out and use multiscan to achieve an actual reset. If you want a detailed explanation of the Twinair technology try this link. It helped me understand why oil viscosity affects the combustion mixture and emissions. It includes pictures (I always find that a big help). https://www.caranddriver.com/features/a16580674/fiats-multiair-valve-lift-system-explained/