Originally Posted by
71/200
You Park your car up for a few days, the oil has returned to the sump or the vast majority of it. After a few days you decide to take the car for a spin. Do you disconnect the crank sensor before driving off? Maybe not, but why not, what is the difference as the oil is in the sump just like after an oil change?
As David has already pretty comprehensively covered, wrong. There's a big difference between leaving your car parked up for a few days and changing the oil. The key difference is that one involves unscrewing the filter, the other doesn't.
Those that have stripped a Scoob engine will know how much oil is left in the gallerys etc after draining the sump.
Yes, and funnily enough, a bunch of people who have stripped these engines (a lot) are the ones suggesting removal of the crank sensor.
Im no technican or mechanic but am i missing something here?
David has already drawn you the analogy of the straw full of fluid. There's an extra aspect to it though. Once the lubrication passages are fully primed, the anti-drainback valve in the oil filter will, as its name suggests, actively prevent the forces of gravity trying to return the latent oil to the sump when the engine is stopped. So, like a straw full of fluid with your finger held over the top.
The fluid lock on both sides of the filter will result in the oil system remaining almost completely primed, even if the car is left for months. However, removing the filter breaks the lock and will allow a significant quantity of oil that would otherwise be held in the system to drain out and be replaced by air.
You can see this for yourself next time you do an oil change. Put a receptacle under the filter, undo it carefully so none of its own contents can spill out, and then see how much oil drains out from "above" it both immediately and over the course of a few hours. You'll be surprised.
Even if you fit a new pre-filled filter, there will probably be a significant quantity - maybe over a hundred cubic centimetres - of air in the system that needs to be purged out. Until *all* of it has been removed, the pressure of the oil throughout the system will be a little inconsistent due to the compressibility of the air - which will, in any case, be making its way "out" through the bearings.
If the engine is running at the time you will have the oil pump forcing air under pressure through the oil system. If it's simply being cranked on the starter, it'll be pumped through at a fraction of the speed and pressure - and whatever oil remains in the bearings won't have to deal with full combustion loads.
I read on here to disconnect the crank sensor after an oil change. That was nearly 10years ago, never done it since and never will
That's a pretty bold statement, especially given you've already exhibited a fundamental misunderstanding of the way the oil system works, and appear to be putting other owner's cars where your mouth is.
Many will do it to be safe
Indeed. It's an insurance policy that doesn't do any harm. So, you think that "being safe" is such a bad thing you don't bother with it?
personally i think its an Scoobynet myth and i will maintain that thought until the evidence is there either way.
When you service cars belonging to other people, do you tell them that you think "being safe" in this area is unnecessary, but offer them the option of doing it if they want you to? How would you go forward if one of these people suffers a bearing failure just after you've serviced their car, searches SN, and ends up reading this thread?
