Oil Pressure Reading

[skyrex4]

Hi

Can someone please explain what my oil pressure gauge is telling me.

I have a 95 R33 GTST which I recently took to a track day. Whilst lapping around the track, my oil pressure gauge was sitting around 6 or slightly above on the factory oil pressure gauge.

When coming into the pit area, the gauge was showing 2 and stayed at 2 whilst I let it idle for a few minutes. When I went out for my next laps it started out at 4 (where it normally sits in day to day driving), went up to and sat at around 6 or slightly above whilst on the track and back to 2 when coming back to the pit area and at idle again. This happened for two more sessions.

On the drive home it sat constant at 4 and has done so since when driving it daily. At idle, once warmed up, it used to sit at 4 also, however, it now goes down to 2 and then up to 4 once driving again.

The oil I am using is a 10W50 and have slightly more oil in the motor to cover any oil starvation issues when cornering and braking. Normally I would be using a 5W30 oil but my mechanic thought the 10W50 would be better for track purposes.

Any feedback would be appreciated.

[zebra]

Rule #1, dont trust the standard oil pressure gauge

[Hadouken]

Rule#2 don't trust standard oil pressure gauge

[Duncan]

but if you did feel like trusting it...it is perfectly normal for it to go up with revs - the faster you rev the quicker the oil pump spins, pushing more oil.

[warps]

As the oil heats up it gets thinner. It's being pumped with a positive displacement pump (kind of - not 100% but for this explanation we'll assume it is), and the pressure is caused by the resistance to flow within the engine (trhough bearings, etc). The higher you rev, the more oil it tries to pump (linearly proportional to the RPM). However, pushing the higher volume of oil through the same restriction causes pressure to rise (there's a bypass which prevents over pressurising the system)

On the track, the oil probably gets hotter than normal, therefore thinner than normal. This is why at idle, the pressure drops away. In normal driving, the oil won't get as hot or thin, hence the pressure remains a bit higher. Synthetic oils tend not to thin out as much at high temperatures, which is one of the reasons they're used in racing.

As the engine wears, the resistance to flow decreases, as the oil paths get bigger (more clearance in bearings etc.). You'll notice the idle speed oil pressure dropping away as the engine ages.

Sounds pretty normal.

Oh, as a side note, the numbering on your oil refers to its viscosity when it's hot and cold (5W30). The first number means it behaves like a single weight 5W oil when cold, and the secong number means it behaves like a single weight 30 grade oil when hot.

Hope that (over simplified) explanation makes some sense.

[skyrex4]

Hi

Thanks for you replies, most appreciated.

I now have peace of mind that all appears normal, however, I will keep a keen eye on it next track day.

Thanks again.

[ARTZ]

how bad is the stock gauge, i mean mine seems to work fairly well..I can easily notice differences in oils as the gauge behaves differently..

Speaking of which, ideally where should the gauge sit on a healthy motor??..

lately mine sits at about 3/4 line on throttle, then on idle slowly drops back to half..never goes under that i have noticed.

i changed to a 10/50...before it was a 5/40 and seemed to drop alot more quickly on idle and not get so high unless pushed hard...

Anyway, is it just normal behaviour and nothing to worry about or should I change back ???

Im tempted to put standard nissan oil in it just to see how it behaves...

[defari]

If this helps but my r33 at wot idles around 3kg/cm2, hard accel it will rise to about 10kg/cm2, using motul 4100

Edited April 14, 2012 by defari