Should my engine stay running if I remove my oil cap?

[Manny D.]

I was just curious if there was a problem with my car because when i removed the oil cap on my car it basicaly dies.. but the other day i seen my friend doing it to his 325i and it was running like normal..

[mojocoggo]

Removing the oil cap essentially creates a massive vacuum leak, and the engine will die after a couple of seconds. How does your car idle?

[a]

actually it depends on the car. Ive left the filler cap off the Borman6 a coupla times. So did BIL, Both cars have Motronic 1.1. It is adaptive enough to compensate.
When I left Banner Elk after 5er fest 03, I topped the oil, and neglected to install the oilcap. The engine started and ran fine. A few hrs later, the low oil level light came on and I discovered my mistake. The engine bay was a mess. The cap was sitting on the top of the air filter housing.

[coopa.s]

Taken the cap off my car and it runs like shit but doesn't die. Sounds like it's about to, but it doesn't...

But usually if it runs fine you have a vacuum leak somewhere.

[rlomba8204]

I was just curious if there was a problem with my car because when i removed the oil cap on my car it basicaly dies.. but the other day i seen my friend doing it to his 325i and it was running like normal..

Why would you do this unless it was an accident? It sounds like you want to know if it will run for shits and giggles. Do you want to potentially damage the engine generally, or more likely the camshaft, due to lack of lubrication?



I will stay tuned for the next post where you ask about engine overhaul or removing the head for camshaft replacement . . . .

[turbodan]

It should run rough with the cap off. It might not die out, but it should make a difference.

Its not going to hurt the motor though. The camshaft gets what it needs from the oiler bar, which is unaffected by the oil cap being on or off.

My turbo car doesnt have any kind of recirculated crankcase ventilation. I fired it up with the valve cover off one time just for fun. It turns out that the M20 uses the valve cover to hold the little peice of steel in place that keeps the rocker shafts from rotating. So dont try that on an M20...

[535is-pa]

i once didnt relize i didnt replace the cap. i drove for about a mile wondering what was wrong. i thought my afm died.

car ran like hell but did not stall and returned to normal once i put the cap back on.

[Manny D.]

Why would you do this unless it was an accident? It sounds like you want to know if it will run for shits and giggles. Do you want to potentially damage the engine generally, or more likely the camshaft, due to lack of lubrication?



I will stay tuned for the next post where you ask about engine overhaul or removing the head for camshaft replacement . . . .

actually i only did it once when i wanted to top off my oil.. and have seen many cars have oil put in while running and even a 1989 325i so i was just curious of there was a slight problem

[Boru]

It does no harm, just creates a big vacuum leak. Air is pulled in through the open oil fill, through the crank case vent an into the intake manifold bypassing the AFM. The engine leans out and dies/barely runs.

[SD45T-2]

if u take the oil cap off you can see if theres Blow By, the car should run the same with or without the oil cap on, If it starts to run like crap. Your PCV is shot.

[rlomba8204]

if u take the oil cap off you can see if theres Blow By, the car should run the same with or without the oil cap on, If it starts to run like crap. Your PCV is shot.

M30s do not have PCV valves. I am also pretty sure M20s don't have PCVs. The crankcase is set up so the exhaust gases recirculate and head back into the intake manifold again. This is why it is not at all unusual to see greasy build-up of sorts on the inside of the intake manifold on the intake side after the breather valve. Not a huge amount, but greasy residue nonetheless. I am not trying to be a dick, but don't send someone off on a goosechase checking for a PCV that doesn't exist on an M30.

I will reiterate that this is a bad idea. Check oil with the engine relatively cold and add at that time if needed. You will get the most accurate reading with the motor cold and the car on level ground obviously. If the engine has run, and you need to check it, let it stand for at least 5 minutes before checking. And when you are done, always double check the fit of the oil cap, that it is tight, and that the dipstick is back in its proper place.

As to the original question, if the engine is running, there is no good reason to remove the oil cap or dipstick to create needless vacuum leaks. It's just dumb. All that incoming air causes the ECU to enrichen the mixture too, which is no good for your cat. And I still don't like the thought of oil spraying out of the engine oil hole. The weak point of an M30 is camshaft lubrication, as it always is with relatively tall motors and I see no reason to risk loss of oil in close proximity to the camshaft, although I see turbodan's point.

[turbodan]

No PCV in an M20 either. Same design as the M30.

[Boru]

All that incoming air causes the ECU to enrichen the mixture too, which is no good for your cat.

The ecu will try to correct back to stoich via the O2 feedback. A vacuum leak of that magnitude cannot be compensated for by the ecu, therefore, the engine goes lean and stalls... no harm to the cat.

The cam experiences no loss of oiling if the cap is removed... except when the engine stalls.

[turbodan]

Luckily, the loss of oiling coincides with the loss of rotation.

[SD45T-2]

if u take the oil cap off you can see if theres Blow By, the car should run the same with or without the oil cap on, If it starts to run like crap. Your PCV is shot.

M30s do not have PCV valves. I am also pretty sure M20s don't have PCVs. The crankcase is set up so the exhaust gases recirculate and head back into the intake manifold again. This is why it is not at all unusual to see greasy build-up of sorts on the inside of the intake manifold on the intake side after the breather valve. Not a huge amount, but greasy residue nonetheless. I am not trying to be a dick, but don't send someone off on a goosechase checking for a PCV that doesn't exist on an M30.

I will reiterate that this is a bad idea. Check oil with the engine relatively cold and add at that time if needed. You will get the most accurate reading with the motor cold and the car on level ground obviously. If the engine has run, and you need to check it, let it stand for at least 5 minutes before checking. And when you are done, always double check the fit of the oil cap, that it is tight, and that the dipstick is back in its proper place.

As to the original question, if the engine is running, there is no good reason to remove the oil cap or dipstick to create needless vacuum leaks. It's just dumb. All that incoming air causes the ECU to enrichen the mixture too, which is no good for your cat. And I still don't like the thought of oil spraying out of the engine oil hole. The weak point of an M30 is camshaft lubrication, as it always is with relatively tall motors and I see no reason to risk loss of oil in close proximity to the camshaft, although I see turbodan's point.

my 86 had a PCV valve, BMW called it something else, but it looked the same as A PCV,AND when i replaced it the issue went away.

[California Dreamin']

No, there is no PCV valve on M30 or M20 engines. This is one reason why these cars are having difficulty passing California's stringent smog tests.

If a car with an M30 engine had an EGR valve, it was added after it left the factory. I have seen one other such car, but it was a motronic 745i turbo. Upon entry to the US the portal state (NJ) required addition of an EGR. So there it was, tapped into the exhaust manifold.

[SD45T-2]

No, there is no PCV valve on M30 or M20 engines. This is one reason why these cars are having difficulty passing California's stringent smog tests.

If a car with an M30 engine had an EGR valve, it was added after it left the factory. I have seen one other such car, but it was a motronic 745i turbo. Upon entry to the US the portal state (NJ) required addition of an EGR. So there it was, tapped into the exhaust manifold.

damn it, if i still had the car i could show u guys, But it makes since.