My passat has 140k Can I use this for my first change in this car. Don't know brand thats in it

This is an additive kit used to flush the engine, protect it, and clean and condition the fuel system. This can be used on the car.

Do I mix all of these with the 8 quarts of oil or do I have to remove some of the oil?

You mix additives exactly in the correct ratio as noted on the packaging. Please see product description of this kit for specifics on how each product is used.

Is the engine oil flush safe for a high mileage engine? My 09 BMW 535xi is at 140k miles and don’t think it’s ever had an oil flush before so I am not sure how safe it is to remove any sludge that may have built up overtime.

Liqui Moly engine flush is comprised of the same additive used in their engine oil. Unlike a chemical flush which is aggressive the Liqui Moly engine flush does the same thing it's engine oil does by dissolving sludge slowly and suspending it in the oil so it can be drained.

Why is the 6 cylinder additive kit listed for the M-B 2.3L Kompressor 4 cylinder engine in a 2002 SLK230?

Some 4 cylinder and 8 cylinder models are included in our application list because kit contents is based on the engines oil capacity, not cylinder count. I apologize for any confusion caused.

Is this kit compatible with the 2.0l Turbocharged motor in the 2015 C300 4matic? I just bought the car used and want to clean it out and replace the oil with Liqui Moly. I see they recommend this as Step 1 but it was for 6 cylinder vehicles.

The correct 4 cylinder kit for your Mercedes is located here: https://www.fcpeuro.com/products/4-cyl-additive-kit-step-1-liqui-moly-lmk0001#desc

Is the engine flush designed to only work with liquimoly oils? I wanted to flush the engine before I put the new liquimoly oil in the car, and I doubt the previous owner used liquimoly oil so, with that being said, would the flush still be compatible?

You can use the engine flush with whatever oil is currently in the vehicle or with whatever oil you want.

Do you recommend using the Fuel System Cleaner before or after an oil change? I read that fuel system cleaners often leave deposits in the oil during the cleaning process and therefore it's generally a good idea to use them close to an oil change.

This fuel system cleaner does not require an oil change after use. It is safe to use at any point whether it is before and oil change or after.

Can this be used in 5 cylinder engines. If so can it be used with a synthetic blend engine oils?

Absolutely! Generally 6 cylinder engines carry a similar crankcase capacity of oil as a 5 cylinder engine. But yes these products will work in either engine. They are also miscible with any type of oil whether it is Synthetic, Semi-Synthetic, or Mineral.