oldusedone

Curious if you could address the Oil pressure light on the RX300 2002? My newly purchased used RX300 got a check engine light at about 3 quarts low, at this point I discovered the Oil pressure light was not working and #4 cylinder had lost compression. The engine started using a lot of oil after this.

When should the oil pressure light go on, assuming it works, in terms of down 2 or 3 quarts of oil. I have asked this and get conflicting answers. Seems to me at some point the pressure will be too low, and a low oil level could be predicted to cause low oil pressure light at some level. In a laboratory setting where oil is drained without affecting pressure how much oil would need to be lost before the pressure light went on?

LexCareSC

Please see the information below located in your 2002 RX Owner's Manual.



Oil

oldusedone

At what low oil level should the low oil pressure light go on? The manual does not say when it might light up. Not sure what the manual means by "extremely low". Seems like a simple physics problem for a car engineer. If I answered a question on a math test with "extremely low" when a numerical value or range is available I'm sure I would get that question wrong. And more than likely did get it wrong given my GPA in college.

Nospinzone

Love your sense of humor, my kind of guy!

But seriously now, the sensor detects low oil pressure, not the oil level. I'm not aware of any car that measures the oil level. They either measure the oil pressure or the oil temperature. My Lexus measures pressure, but both my Harley and my Ferrari measure oil temperature. In none of the 3 vehicles do I know the oil level from the gauges or the Lexus idiot light.

In the case of measuring pressure, you car could have all 9 quarts of oil and still get an oil pressure warning because a line or the filter is blocked. It would have nothing to do with the oil level. The oil level is a factor in tripping the sensor, but it depends on other factors. For instance, if you are running 5W10 motor oil, your oil pressure will read less than if your car had 10W40 oil. The higher viscosity oil will increase oil pressure.

Anyway, the only true way to know your oil level is to check it with the dipstick. From what you said it appears that one of your cylinders is burning oil. Depending on how much means either getting new rings or living with adding oil periodically.

lobuxracer

iTrader: (2)

My '93 Supra has an oil level and an oil pressure light. So did my '06 IS350 and does my '08 IS F. It's a common feature on upscale Toyota and Lexus engines. I am surprised the 2002 RX300 does not.

oldusedone

We live in a world where dip sticks have disappeared on some newer cars. Oil levels are monitored via sensors and gauges exclusively. Hybrids may not even have a oil pressure or an oil level indication. Do some cars have neither an idiot light/gauge for oil pressure/oil level nor a dipstick? A self contained engine without any oil monitoring other than something that tells you when to change it? I don't know, but I'm sure it will come to this at some point even if it has not happened yet.

On my RX300 there is no oil monitoring gauge as the oil pressure light does not work. I know this because the photo in reply #26 here: https://www.clublexus.com/forums/rx-...e-rx300-2.html shows the absence the oil pressure indicator when the key is turned to the on, prior to starting the vehicle. Either the sensor is malfunctioning, the bulb is out or the wires are not connected.

Had I known to check these lights prior to purchasing the vehicle, in hind sight, I would have passed on the car. Should my mechanic have noticed this problem when I brought it to him for an after purchase check over of the workings of the car? Am I wrong to silently resent him for missing that missing light? Would knowing the oil pressure light was not working made any difference anyway? Consumers Reports says one of the things you should check on a used car is, are the dashboard lights all working. I did not check them, would checking those be part of the routine a mechanic should check when asked to do an inspection for a gullible used car purchaser requesting a check-over? Had we known the oil pressure light was broken, would we have checked the oil prior to blowing #4 cylinder head and needing a new engine? Can't say, but I know I will be way more careful about these lights in the future. Never again will I be afraid to look over the dashboard lights and make sure everything is in order. On the other hand, I doubt this same problem will ever come up again.

Which brings me to my original question again. On an engine in a laboratory setting, what low oil level would cause the oil pressure light to illuminate? Given the fact this sensor is not designed to check oil level at some level of low oil it must be triggered simply because pressure cannot be maintained with (X) amount of oil. One quart, two quarts or three quarts down, in a lab setting there would seem to be a consistent level that would trigger the sensor. Can engines be designed and tested without knowing this number? I don't know, maybe the data cannot be divulged for some other reasons?

lobuxracer

iTrader: (2)

Not even Lexus engineers can answer this question. There are far too many variables in the equation to say any given level will cause low oil pressure, and "low" oil pressure is also not well defined by itself. There is a range of pressure considered acceptable for the oil pressure switch to indicate low pressure. Your quest for this answer is Quixotic.

oldusedone

My sense is that if ten engines were running all hooked up to a variable oil level machine (don't worry I'll make one if they don't exist) there would be a range of low oil levels where the oil pressure light would go on. Indeed, there maybe no known number, but it seems to me there really is only one variable here, what level causes the low pressure sensor to illuminate the low pressure indication? Could this number be calculated using fluid mechanics? Not by me it couldn't, but maybe someone could.

nevernu

excuse me for jumping in here, was just browsing and wondered how this applied to my 2007 es350... according to the manual they check oil pressure by removing the sensor switch and inserting a pressure gauge. According to them the pressure should be at ...

ENGINE CONDITION OIL PRESSURE
Idle 80 kPa (0.8 kgf*cm 2, 11.6 psi) or more
6,000 rpm 380 kPa (3.9 kgf*cm 2, 55.5 psi) or more

surely there is a similar standard for the RX below which is "low oil"

Edit on rereading the thread I guess the question really was how much /little oil/ or faulty oil pump will drop pressure before spec and trigger sensor/light...

ok I'll move along now

lobuxracer

iTrader: (2)

How much/how little, how hot or cold is that oil, what weight is the oil, how worn are the rod and main bearings, how worn is the oil pump, how worn is the relief valve on the oil pump, how much varnish build up is there in the oil galleys, how much side clearance is on each of the rods, how much end play is there on the crank...

The number of variables is staggering which is why a pressure switch is useless for determining oil level.

oldusedone

All engines are brand new, broken in, with identical run characteristics. Wear is not a factor and each is at the same temp. This is a laboratory setting.

Humans get high blood pressure when plaque and deposits adhere to the arterial walls. Can cars get high oil pressure too?

lobuxracer

iTrader: (2)

Only if the relief valve fails closed or the filter becomes clogged. By the same token, if the spring in the relief valve fails, your oil pump might not make adequate pressure at low rpm, but work fine at high rpm. Your laboratory results will be worthless in the field for all the reasons I mentioned, and few I didn't like manufacturing variance within acceptable tolerances for all the parameters listed, and the switch itself. Some oil pressure switches close at 6 psi. Some close at 10 psi. All close somewhere between 6 and 10 psi on automobile engines and are considered acceptable in service.

Humans get high blood pressure from stress too. Ever taken the blood pressure of a world class cyclist after a long stage? If it were not for knowing it will come back down when the competition stops, a doctor would prescribe medication. Same thing with body temperature. Competitive athletes have indicated sustained body temperatures of 106F in the heat of an event without brain damage, and yet if one were to show up at the ER with this temperature, the staff would immediately take action to reduce the temperature.

Your analogies are not working well and are only underscoring your unfamiliarity with engine design and operation.

The simple answer is, it is impossible to reliably estimate oil level with a pressure switch. You need a level switch or a level indicator. Toyota has used level switches on both of the engines in my signature. Clearly they did not on the engine in your RX.

oldusedone

Thanks for taking the time to help fill in my gaping wide lack of knowledge regarding engine design. I definitely feel like I'm learning a bunch, even if the horse is out of the barn. If you are saying the pressure switch used in the RX300 has an operating range of 8psi +/- 2 psi, then even if you add in all the manufacturing variances on the engine there still would need to be a range of levels for the low pressure switch to operate. If you add up all the variances in bearing clearances and the other stuff I don't know about, you could come up with a +/- fudge factor to say if an engine has X amount of oil in it, the pressure switch will operate with a probability factor of Y. Sorry for not letting this go, but I think these numbers are know, or were know at one time, by the Lexus engineers. Every part has a range of acceptable tolerances, anything outside that range is a no-go and should be tossed into the scrap heap. I like my example, ten Lexus engines would have little variability in machined characteristics, but that's just my opinion, based on the reported high quality product they claim to produce.

The hidden question here is am I justified in being upset the mechanic who checked the car over for me failed to see the low oil pressure light was non-functional? Would knowing this failure possibly have changed my eventual fate of blowing out a head after 300 miles of highway driving? I suppose there is no way to answer that question but I do know had I the smarts to check the indicator lights before buying the car I'd never had made the purchase. Hind sight is a great thing, is it not?

lobuxracer

iTrader: (2)

Oil pressure will not cause a head failure. Ever. It will cause bearing failure first, cylinder scoring second, and cam journal failure third. If you lost oil pressure and someone told you only the head is damaged, they lied to you or it was not an oil failure.

oldusedone

OK, you caught me, I don't really know what "blowing out a head" means. I'm referring to loss of compression in one cylinder, around 20 psi, which I thought might be a result of a cracked ring or scoring of the wall.