oil pressure vs. oil quantity - Honda Prelude Forum

PilotSH · 07-19-2002, 03:45 AM

For VTEC (and non) preludes, is there a point where as the oil quantity goes down, so does the oil pressure? What I mean is, lets say that an engine is running with 5 quarts of oil (the upper hole on the dipstick). Now if it only had 4 quarts of oil (lower hole of dipstick), and I revved it thru the entire RPM range (car is stationary), would the plot for the oil pressure look the same? That's what I assume. My thinking is that as long as the oil supply has a continuous flow of oil going to it (no air at all), that the pressures should be the same, regardless of how much oil is in the engine. Now it will get to a point where if there isn't enuf oil in the engine, that the oil pump will start to suck up some air, and the pressure will drop. So if I had 3 quarts of oil, as long as hte supply of oil to the pump was continuous, it will provide the same amount of oil pressure as having 5 quarts.

When exactly will the oil light in our cars light up?

The reason I am asking this question is that I've been running with a very low level of oil for the last few weeks. I totally forgot to check/fill the oil, so the car got down to about 3 quarts. During the whole time however, the oil light never once came on. Did my engine take any damage/increased wear from having such a low oil level, although the oil light never came on?

marcucci · 07-19-2002, 06:03 AM

Quote:

Originally posted by PilotSH

My thinking is that as long as the oil supply has a continuous flow of oil going to it (no air at all), that the pressures should be the same, regardless of how much oil is in the engine. Now it will get to a point where if there isn't enuf oil in the engine, that the oil pump will start to suck up some air, and the pressure will drop. So if I had 3 quarts of oil, as long as hte supply of oil to the pump was continuous, it will provide the same amount of oil pressure as having 5 quarts.

This statement is entirely correct.

Quote:

When exactly will the oil light in our cars light up?

About 2psi, I believe. When that light comes on, damage is ocurring. How much is a function of how long it is on. If it is on for any length of time at high RPMs, you can be sure that the damage will soon be extensive.

Quote:

The reason I am asking this question is that I've been running with a very low level of oil for the last few weeks. I totally forgot to check/fill the oil, so the car got down to about 3 quarts. During the whole time however, the oil light never once came on. Did my engine take any damage/increased wear from having such a low oil level, although the oil light never came on?

Yes, you probably saw increased wear unless you idled, stationary, the whole time. When driving and moving around you probably were drawing in a little air and your pressure was down a little bit. More than likely, since you never saw the light, it was not "extensive" and probably did nothing more than shorten the life of the motor. Consider it like smoking; you may not have cancer but you've probably taken a few years off your life. Watch your level like a hawk in the future.

Mugenlude · 07-19-2002, 06:57 AM

James, James, James...

I make it a ritual to check my oil before autocrossing every weekend. You could do this, oh yeah you haven't raced the Prelude in a while.

PilotSH · 07-19-2002, 03:08 PM

Thanks Marcucci. Well, I changed the oil today, but Walmart only had a couple of Mobil1 5W-30 Synthetic, so I bought a couple 10W-30 Mobil1 Syns and am now running 3 quarts 5W-30 and 2 quarts 10W-30. So would that make my oil 7W-10? :P hehehe

Mugenlude :P hehe. Dun worry, I 'll be out full force with the Lude this Sunday. I shall kicketh major gluteous maximus. Hopefully I'll be able to kick the tail out with drop throttle oversteer and trail-brake oversteer with the experience I gained from autoxing the Miata.