Accuracy of dipstick

[Sandspider]

ORIGINAL: 944 man

ORIGINAL: Sandspider

Simon - that's what I thought, but I couldn't see how the dipstick could be accurate if everything else was working. Turns out everything else probably isn't working (oil pressure warning light) though oil pressure still remains healthy.

Re-reading what Id written, it did seem to be rather facetious: which wasnt intended.

Simon

That's OK, I didn't think it was facetious - I actually couldn't figure out how the dipstick could be wrong either, because as you say, it's a stick sticking into the sump!
Which now leads me to wondering whether my oil pressure gauge may be inaccurate too. (5 bar under acceleration, 4 bar at hot idle). This is pretty much the same as it was with the 10W40 oil, but surely if my oil system is now half (or more) empty pressure should have fallen..?

 

[944 man]

As long as there is sufficient oil in the sump, in order that the pump doesnt suck in any air, then your oil pressure will remain unaffected. Your oil pressure relies on the condition of the oil pressure pump, the main bearing faces, the main bearing journals on the crank and constant replenishment of the supply to the pump to be pressurised; and little else. Your oil level will only affect your oil pressure when it is so low that the pump sucks in air as well as oil.


Simon

 

[Hilux]

Which now leads me to wondering whether my oil pressure gauge may be inaccurate too. (5 bar under acceleration, 4 bar at hot idle). This is pretty much the same as it was with the 10W40 oil, but surely if my oil system is now half (or more) empty pressure should have fallen..?

If the oil pressure gauge is reading anything and the oil or warning light is not on then you have oil circulating. The pressure gauge will inform you of the pressure within the system and (subject to pump and engine condition) can vary. If the level drops below the pick up pipe in the sump then you will lose pressure so until this happens a lower oil level will not automatically mean a lower oil pressure.

What a low oil level does is reduce the amount of heat taken away from the engine as there is a smaller volume of oil circulating for many people do not realise that apart from seperating surfaces and reducing friction betwen moving parts its other main purpose is to remove heat (water does not circulate along the crank etc)

If you are getting 4 bar at hot idle your pressure seems absolutely fine although it seems a little high compared to most I have heard about. Remember also that the crank oil requires volume as you can only squeeze so much oil through the journals which is why (back) pressure drops when bearings and journals wear.

The low pressure warning lights come on at quite low pressures (as low as 5 psi in many cars)

Edited to say I`ve just posted and seen the reply above[]

 

[Sandspider]

Thanks chaps - that explains the consistency.

Oil pressure has always been high since I've had the car - so much so in fact that I thought my oil pressure sender unit might be broken (apparently a common problem). I mentioned this to my indie, and he said 4 - 5 bar was perfectly normal & acceptable for a 944. So I've let it be!

Thanks again.