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the crankcase, or at least I don't believe it's supposed to do that.
The dipstick tube leads into the bottom part of the engine (the crankcase), which IS NOT where ignition, compression, and combustion occurs. It's where the oil sump (oil pan) is, and where the "bottom end" components swing and thrash around (like the piston connecting rods which are connected the crankshaft, itself).
Each cylinder keeps its pressure inside itself during the compression stroke and power stroke (two of four phases in a four-stroke engine, other 2 are intake stroke and exhaust stroke). Cylinders are sealed at the bottom (by piston rings) and the top (when intake and exhaust valves are both closed, and also head gasket must be good, because the head provides a "top" to the open block and houses the valves). This keeps the pressure produced through combustion IN the engine block (in the actual cylinder bores) to drive the piston downward (which connected to crankshaft, to flywheel to transmission to wheels, drives the car).
If the cap is left loose or left off the dipstick tube (on 900s, anyway), IT WILL AFFECT how the engine runs, though. (It usually dies!) An open dipstick allows too much unmetered air into the crankcase. The reason that causes problems is that crankcase gases--miniscule amounts of gas which escape the piston rings,etc.and wind up in the crankcase--get recirculated back into the engine (on modern cars, by federal law) and drawn into intake manifold through crankcase ventilation hoses. This extra, fresh air makes the engine run so lean that it usually dies (at least on the 8-valve, CIS 900s).
If you already knew this, I didn't mean to insult your intelligence. I can't explain things very well and I have to lay out the whole picture (probably more to reassure my own brain than for others' benefit!). I just hope I've remembered my facts correctly!
I hope this helps!
Micah in NC
'84 900S, 219K mi.
posted by 216.77.232...
, Thu, 22 Aug 2002 12:19:08, Thu, 22 Aug 2002 12:49:21, Thu, 22 Aug 2002 14:50:53, Thu, 22 Aug 2002 15:09:53
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