I don't know about the 4000, but there are two ways to check the oil level on the 2800, and only one is correct. On the 2800, you can check the oil with the dipstick plug screwed in or not screwed in. The correct method (from the owner's manual) is with the plug _not_ screwed in, just resting on the lip of the hole.
Checking with the plug screwed in will result in the oil level being low.
If the 4000 uses a threaded dipstick, check your owner's manual to be sure which way is right for yours.
Jim, "Mo' coffee!"