318is, revs drop when oil filler cap removed

[heywood100]

just joined and used search but cant get an answer.

i a going to buy a 318is (my first BM) this evening. cant wait.

one thing i dont understand is this.

when i remove the oil filler cap the engine rpm drops a lot and it nearly stalls.

similar but not as extreme when i remove the dip stick?

any ideas?

appreciate it

John

[jason325i]

not a garantee but apparantly from someone in the know because of something to do with the oil system on the bm its better that the revs drop when you remove oil filler or dipstick shows there isnt a seal problem hopefully this is the truth

cheers jas

[Mach 5]

This is normal. The engine is under a vacuum when it is running and by opening the system, taking the oil cap off or the dipstick out, you are introducing alot of air into the system. It is similar to having a massive vacuum leak. One of the techs chime in if I am wrong.
Ben

[WickedBimmer]

Yep, i have that car... the Whole Engine is on a Vacuum System, if u remove just one cap, it will change the entire reving of the car!!!

hope this helps!

(yes its completely normal, to answer ur question!)

[Torque]

pretty normal... unless it squirts oil everywhere when you take it off

[heywood100]

thanks guys, glad to have added the 3rd German car to the stable

[TECH]

Yeah, it's normal. Ever heard of the PCV system? Basically, it pulls the crankcase vapors into the intake manifold, and reburns them. By opening he cap, you let a lot of oxygenated air into the system, making it run lean.