94 S500 low oil ps at idle

our 94 s500 is having low oil ps at idle is almost 0 tap the gas and it goes up. any ideas what is cauising the low ps at idle

[ddrake3]

What viscosity oil are you using? Also, it's normal for oil pressure to drop at idle. The oil pump is driven by the engine, so its speed varies with engine speed. At lower pump speeds (at idle, for instance,) the pressure will be lower. Also, if you are using a very low viscosity oil (flows more easily,) then your pressure will be lower at all speeds than it will be with a thicker (higher viscosity) oil. It's easier to pump thinner oil which means it takes less pressure to pump it through the engine.

Hope this helps,

Don

straight 40 are u suggesting lighter oil?

[Ali Al-Chalabi]

Exactly how close to zero is the oil pressure?

Lighter weight oil will result in lower pressure, so you do not want lighter oil.

very close to zero lifter some times make ticking sound unlit the oil goes up

[engatwork]

Cold starts on straight 40 wt is, in my opinion, not a good thing. I would think you would be alot better off using a multigrade (20w-50 wt), high quality oil. Excessive clearance between the bearings, crank, etc and oil pump can cause the low oil pressure. What kind of frequency has the oil been getting changed at?
Ya'll please don't let this start another oil thread - it is just my opinion.

we just got the car about 11k miles ago uses no oil so far i will
change it to 20w50 next week thanks for the help

[pilot2000]

I noticed My Oil Pressure went to 0 today after driving for a long time.

It only does that at Idle, and once you hit the gas, up it goes. And if I only drive the car for a short time or even as much as an hour it is fine never goes to 0 sticks around 1.5 or so at idle, it is time for an oil change on mine and I use 10W-30.

Should I stay with 30 or go to 40 it is cold here, so I think lighter in the winter will be better for starts.

What you guys think?

I don't want to start an oil debate either. Clean is best in my opinion.

Thanks everyone.

[Ali Al-Chalabi]

Pilot,

Do you mind paying the price for Mobil 1? If not, Mobil 1 has introduced a new 0W-40 motor oil, which you may want to consider. However, I have yet to find it in stores, I think it may still be a dealer-only item.

[400E]

I agree with you, Ali. I've been looking for Mobil 1 0-40 unsuccessfully. I have been using Mobil 1 5-30 in winter, 15-50 in summer, but until the 0-40 is available will probably stick with the 15-50 all year long in the future. I've heard from a number of folks who live in colder parts of NA than Omaha who say 15-50 works great in winter. (Specs say it's pourable until -54 degrees F or so.)

My idle oil pressure went from 0.5 to 1.5 in summer when I made the switch to synthetic.

[pilot2000]

Sorry to be of little knowledge but what is 0W-40?

Is it lighter, heavier, for high mileage? I am assuming it is synthetic

I did find 0W-30 is that similar?

Thanks

[400E]

Mobil makes a 0-40 formulation of its synthetic, Mobil 1. It is the standard viscosity that many MB dealerships use. It covers a lot of temperature range, and is better suited (some feel) for V8 engines in particular, esp. those that tend to "run hot." The larger number of any multi-viscosity oil describes the ability of the oil to resist thinning out at high temperatures. The higher the number, the more heat the oil can tolerate without thinning out.

[mplafleur]

I've heard that .7 bar is the minimum oil pressure you should have while running the engine. While oil viscosity sure can have an effect on your oil pressure, the higher oil weight should result in higher pressure. Being in Florida, I wouldn't expect that straight 40 should be a problem, any time of the year. It's plenty warm enough. Only up north here would I start to question cold starts with heavier wieght oil.

My engine was doing the same as yours. It would go to zero at idle. If you bump the throttle to raise the RPM only by about 200-300, the pressure would rise to about 1 bar. If this is the case, my guesss would be worn main and rod bearings. More I think from the main bearings. You've got too much oil leaking out of the bearings to keep the pressure up.

I replaced my rod and main bearings when my timing chain broke. I did nothing to the pistons, cylinders or the crank. My oil pressure at idle is now just above 1 bar.

Now, it is possible that it is the oil pressure sending unit or the gauge might be faulty. You might want to check these before rebuilding the bottom end of your motor.

Does the pressure seem ok right after you start the car? Does it go to 3 bar within 3 seconds? An indication of the worn bearings is high pressure at cold and zero pressure when the oil is hot.

SINCE I CHANGE THE OIL TO 20W50 IS DOING OK NO MORE ALMOST ZERO PS IT STAYS AROUND 1 OR MORE EVEN HOT BUT A COLD STARTS IT GOES TO 3 AND STAYS THERE FOR A WHILE AFTER THE TEMP GOES PAST 80 IT GOEST TO 2 OR SO

[pilot2000]

My pressure went down to 0 again today at idle and I have just changed the oil on Saturday so I know I have good oil, I have Synthetic in there. And my pressure does go to 3 once the car is first started. Does that mean I have worn bearings and what is the magnitude of this job?

The red warning light even came on today for the oil pressure at idle. Could it be the sending unit as the pressure tends to fluctuate very much and the needle does not move up or down steady, it jumps.

Or is it my oil pump. But if it is the oil pump wouldn't I experience a loss of power, which I don’t at all.

Thanks.