Removing oil fill cap after sitting drops oil on dipstick

[Tuesdak]

I wouldn't think checking the oil level would be a challenge on a Cummins engine. I have a sloped driveway so I tend to check the oil after a short cold run to a flat parking lot and sitting for hours. The random oil filter draining back or not and oil expansion when hot give me readings all over the place. I figure the filter doesn't drain back cold. Oil level is up a quart when hot. Checking the oil the same exact way has the level going down somewhere between 500-1000 miles per quart.

One oddity I can't pin down is why opening the oil fill cap, even after sitting for hours (hot/cold doesn't matter), will dump oil on the dipstick. I check the dipstick as many times as I want, but, after I remove the oil fill cap oil appears to be dripping on the dipstick. I can only find a obscure reference to a TSB about removing the oil fill cap during an oil change. Is oil vacuum trapped in the head somehow?

The breather/oil separator on the engine is new and after breaking the old one open there isn't a filter in it of any sort like newer years may have. Separator stuff yes. It was replaced as it's drain tubing was leaking. So this 'open box' doesn't make sense that the oil fill cap would affect anything in the head. Is there a check valve in the breather to the atmosphere I am overlooking?

 

[Tuesdak]

Pulled stick out of engine 3 times and get this reading after sitting 3 hours.

Remove oil fill cap and a bunch of oil drops on the dipstick.

 

[cerberusiam]

I would run a quart of MMO in the engine a 1000 miles before next change and see if that changes anything. Whenever I see weird reading son the dip stick, it is time to clean up the oiling system.

 

[User113]

It shouldn't be a vacuum issue, note that once you pull out the dipstick, you have "unsealed" any possible vacuum if there were any to begin with. It is very unlikely that there would EVER be any vacuum in these engines since they are vented to the atmosphere through the valve cover breather (and the dipstick tube once it is pulled past the o-ring). This is very strange indeed.