oil pressure problem/question

[Raddy]

Hi
Today I noticed strange thing with my oil pressure gauge. I driving at the higway at about 3.5k rpm, oil pressure is normal. Then after few minutes I noticed that oil pressure starts dropping slowly. First reaction was lift off accel. pedal. When rpm drops about 200rpm lower, oil pressure jump back to normal value. I found that if I hold any rpm for longer time, oil pressure gauge begin to show decreasing of oil pressure. If I partially lift off from gas and rpm drop for about 200-300rpm, oil pressure jump quick back to normal values and this is same in different rpms....
Oil pressure is normal at idle or 3000rpm. Also, when driving on country roads and often change position of gas pedal, pressure is normal. Oil is 10W-40.

[Barryjdart]

What guage have you got. Could just be a bad earth on the sensor if it is an electrical one.

[Raddy]

it is electrical Autometer gauge, sender attached in place of standart oil warning light sender.

[arry]

it's a symptom of being low on oil!

[driftalot]

check the oil feed pipes 4 blockage and use 10w 50!!!

[Ivor]

did you wrap the sender in ptfe tape when you fitted it, if so you might have a bad earth.

[nene]

it's a symptom of being low on oil!

This is my first thought too

Holding the engine at high(er) RPM will increase the amount of oil being drawn up by the engine, resulting in the volume sitting in the sump dropping. When there is insufficient oil in the engine, the oil that's been drawn up won't have time to make it's way back to the sump before it's needed again, and the oil pickup will become exposed

Before you start panicking, check the oil level Remember to use the SXOC-approved "squeegy" technique to use the dipstick to scrape the oil out of the inside of the dipstick tube before you take a reading.

[beeston_pete]

squeegy technique??? This could explain why mine appears full but didn't seem to take much when I changed oil last... What do you do exactly??

[Vova]

check the oil feed pipes 4 blockage and use 10w 50!!!

That won't help, 10W40 vs. 10W50 only gives a slightly bigger range in which oil is not affected by tempereature.

[Raddy]

oil level was at full.
if low oil level will be reason, why I get high (correct) oil pressure in high rpm when accelerating (not holding speed)? This problem appear only when holding same speed....realy strange to me

[nene]

squeegy technique??? This could explain why mine appears full but didn't seem to take much when I changed oil last... What do you do exactly??

Leave the engine to sit, hopefully the oil will dribble down to the bottom. Hopefully. It's usually best to leave it overnight, but 10 minutes should give you an acceptable reading.
Pull the dipstick out, look at it, rotate through all four sides, and make a note of the level on the lowest side of the blob thing, if there is any portion of the blob with no oil on it then the lowest point of that is the reading - it's not uncommon for the oil to be smooshed in such a way that it looks like the engine is a little overfilled, when in actual fact it's right at the end of the dipstick.

Wipe it off with a lint free cloth. This is important, you don't want little bits of fluff in your oil, right?

Push the dipstick in until the plastic thing on the end of the wire meets the top of the tube, at this point the stupid little blob will have gone through the tube, but won't yet be in the oil. Pull it out and wipe it off. Repeat this until the little blob thing on the end comes out with no oil on it. It may take anything up to six attempts to use the blob thing to squeegy the inside of the tube.

Push the dipstick in firmly to the end, and then pull it out smoothly. Once again rotate it so you can see all four sides. Assume that the lowest one is the real level of oil, because the designer, in their wisdom, decided it would be too hard to have the dipstick enter the sump vertically. You may have to go through all this several times to get a sensible reading.

When you pull the dipstick out, it has to take a convoluted path around the oil pump (yay, go nissan design team!) which makes the blob thing rub against the sides. Oil gets transferred both ways, which is why you get silly readings.

Two words:

Be Paranoid

The CA18 dipstick is absolutely shite. I lost an engine through not being aware of how to read it properly, don't make the same mistakes.

oil level was at full.
if low oil level will be reason, why I get high (correct) oil pressure in high rpm when accelerating (not holding speed)? This problem appear only when holding same speed....realy strange to me

Whilst you're accelerating, the engine will still be drawing from the pool of oil in the sump. Sooner or later that will run out. What usually happens when you have enough oil in the engine is that there's enough oil to mean that the oil that's been sucked up dribbles back to the sump and replenishes it before it falls below the level of the oil pickup. As soon as you lift off, the oil pump doesn't suck up as great a volume of oil, and it has time to dribble back to the sump before it's needed.

Seriously, check the oil level using the method above The only other alternative really is a failing oil pump, and whilst a new pump is nice to have you'll feel pretty gutted at shelling out for it if the problem was just low oil.

[beeston_pete]

Nene !!