On small engines that have an oil dipstick that doubles as the cap covering the oil fill port, if the cap is threaded, how do you read the dipstick? After wiping it clean, do you insert and thread it, then unthread it and withdraw and read? Or do you insert it until the threads touch, then withdraw and read?
I have several items like this. On the Honda mower, the instructions say you insert until the threads touch, then withdraw and read. None of the other instructions say one way or the other. It is typical that the length of the thread engagement is something like the length of the ADD to FILL region on the stick, so the same oil level says one or the other depending on the method.
It occurred to me that other people must have the same question so I spent some time hunting around. It seems pretty evenly matched between “thread all the way in” and “don’t thread”, but I am surprised that about a quarter or so of the people answering these threads basically say it isn’t easily answered. Some say you are expected to completely drain the oil, add exactly what the manual said, read the dipstick by any method you like, and then use that as your standard – stick with that method and try to keep the oil where you saw it the first time. Others say you aren’t really supposed to use the dipstick to check the oil (which is news to me), you’re not supposed to check it at all, you’re supposed to use some other means to check the oil, and a bunch of bizarre other stuff.
A couple people pointed out that companies even give out conflicting information about which way to do it for one product, and some say the method differs from model to model within one manufacturer and even from year to year for one model. Weird.
I think dipsticks ought to work and make checking the oil level practical, and I’d think oil level is important and changeable enough to be worth monitoring. That this is such a difficult thing to resolve is pretty surprising.
I used to have access to assembly prints for those things and the parts that go into the assemblies. Nowhere in those prints did it give an indication to what the engineers intent was. I wouldn’t be surprised if the engineers that had that knowledge are not at the company that owns the tools anymore, so the intent of how the reading is to be taken is not known by the manufacture of the engines anymore. Details like that get lost with personnel changes.
On my Honda motorcycle, it is the same, insert but don’t thread.
I had assumed that, while having too to high of an oil level is certainly a bad thing, being a little over full was better than being too low, since being too low is a really bad thing. To my thinking, the insert but don’t thread method is a better way of making sure you have at least the minimum. I don’t know if this reasoning is true, but it helps me remember what to do.