04-09-2004, 12:47 AM
Well I give up. I'm sure I could buy a book or something, but I'm not gonna do that, asking a few others gets me nowhere, and internet searches have failed me. I was even desperate enough to send a request to HowStuffWorks, with no result. Everyone seems to know how to test it, what it does.... but.... Where does engine vacuum come from? and where/why is it used? How (or is) it regulated? OH! And why don't diesels make a vacuum?
From what I've gathered, it comes from the air rushing through the intake. Makes sense that if you hooked a hose into that, the air going by would create a vacuum, and it would increase as load increased, like it does in a car. Case closed? Somehow I don't think so, because why couldn't a diesel do the same thing? And I understand how it's used for driving all kinds of things-- brake booster, timing advance (on old cars like mine), cruise control, all kinds of fun stuff. But why is the top of the head under vacuum? Just to make sure fuel/oil vapors don't build there? Kind of the same reason the crankcase is kept under light vacuum (as regulated by a PCV valve in many cases, which itself is even vacuum driven?) ? Mostly I want to know where it comes from. Hook me up. I hope at least a few others don't know and this isn't just a super dumb question. :lol:
From what I've gathered, it comes from the air rushing through the intake. Makes sense that if you hooked a hose into that, the air going by would create a vacuum, and it would increase as load increased, like it does in a car. Case closed? Somehow I don't think so, because why couldn't a diesel do the same thing? And I understand how it's used for driving all kinds of things-- brake booster, timing advance (on old cars like mine), cruise control, all kinds of fun stuff. But why is the top of the head under vacuum? Just to make sure fuel/oil vapors don't build there? Kind of the same reason the crankcase is kept under light vacuum (as regulated by a PCV valve in many cases, which itself is even vacuum driven?) ? Mostly I want to know where it comes from. Hook me up. I hope at least a few others don't know and this isn't just a super dumb question. :lol: