Underbody covers
 

Is it good idea to drive without the underbody covers in summer? Do they do anything with aerodynamics except keeping off the water and splash in winter times. I have them off become one is damaged. Thought would be better off for engine and transmission in summer to cool faster.

Under body panel.

Protects the under components of the car from getting damaged by let's say a rock. Though it's not 100% effective, it does help somewhat. Or anything that may cause damage to the engine from entering. Example you are driving and ran over something on the road. Without the under body panel, that item can enter your engine area and get lodged into the belts, puncture your oil pan etc.

If you live in areas where it's constantly raining or snowing. The panel will help shield your engine from corrosion etc.

Not sure about the aero dynamics.. I think it does help keep the engine cool somewhat. There are certain vents at the bottom they seem to be channeling air to certain parts of the car. I could be mistaken though.

Really there is no reason to remove the under body panel.

It definitely helps with aerodynamics, you'll see the difference in your gas mileage.

It will help with aerodynamics, and to some extent gas mileage, but only at highway speeds.

Margal, if I were you, I'd drive around without panels only if I was investigating a fluid leak. Otherwise, I'd put them on.

With the way everything is designed, there is no overheating problem for engine and/or trans.

+1000

The presence of under body panels creates a smooth stream of air under the car, reducing unwanted body lift and improving handling at high speeds. This is accomplished by reducing turbulence caused by the slip stream under the car hitting obstructions and tumbling, rather than flowing smoothly.

And although it may not be apparent, there are also slip streams designed by BMW that travel through the engine compartment and exit the under body panels causing improved cooling of the engine and transmission by design via smoothing airflow. These are much more effective than leaving the belly pan off the engine.

BMW has been a leader in under-chassis aerodynamics for twenty years, with many competitors just recently catching up. Some of the experience was undoubtedly learned in the days when BMW was an aircraft engine manufacturer, prior to building cars.

This slipstream effect for component cooling was learned in the early days of aviation as designers compared leaving the engine exposed to the airstream as opposed to building panels around the engine to smooth the air. Although it seems counterintuitive, enclosing the engine (cowling) creates a coherent stream of air next to the engine, which increases convective cooling, lowering engine temperature.

Bottom line: As pcy says, leave your panels in place and the car will run cooler, handle better and keep components cleaner.

Thanks guys. Now I understand. This thing is not cheep but seams I need to order a new one. Does anybody know the part number for oil drain and filter access panel for manual transmission? Can't locate it in realoem. I am missing it too.