No oil pressure at idle?

[ninjazombiemaster]

Hey guys, last night I noticed my car wasn't reading any oil pressure at idle. It seems to have started after I had to jump it several times because I left my lights on. As I drive, the pressure climbs and then gets to about halfway up the meter and stays until I idle again. I looked

Something wrong with the sending unit?

Possibly a leak?

Maybe the oil filter or oil itself?

I did change my clutch lost a little oil, but there was still an acceptable amount in there as far as I'm aware.

I'll see if I can get my hands on a mechanical gauge. I get a gut feeling its gonna read normal. I cant work on it right now, so I'm hoping you folks had any other suggestions on what to check so I can make effective use of limited shop time. Thanks.

[Virto]

A mech gauge is your best bet, as you mentioned. What weight oil? At idle, my factory gauge reads very low with 10W30 when hot.

Might need a little heavier weight oil, but I'd rule out the pressure sender first.

[ninjazombiemaster]

I think its 10w40, but I'm not the one who put it in. That being said, its the same oil it had when it was working. Its warmed up quite a bit here - so its possible that it is the oil just never noticed before.

[tlorber]

Changing your clutch should have nothing to do with oil loss (at least not from the motor). Do you hear any valve clacking when the pressure reads low?

[Lazeum]

What is the color of your oil sender?

I'm asking it because I had no oil pressure at idle (whereas my engine was fully rebuilt). I've swapped the golden sender with my previous unit: black. Oil pressure at idle became ok at 1/3 of the oil range and above 1/2 when driving it.

It was just a bad sender, new units in gold color are not as good as original one which were black (to be sourced at Nissan's)

Edited May 16, 2013 by Lazeum

[ninjazombiemaster]

Changing your clutch should have nothing to do with oil loss (at least not from the motor). Do you hear any valve clacking when the pressure reads low?

I don't hear anything out of the ordinary from the engine. That being said, I'm sure my valves could use a

I'll take a look at the sender when I go for my lunch break and see how it looks.

[Stanley]

Can't hurt to try a new oil filter.

[ninjazombiemaster]

Can't hurt to try a new oil filter.

Surely couldn't. I've got a spare filter laying around somewhere, I'm sure. Guess I'll also top it off while I'm at it.

Also, I looked at the sending unit, and there's enough patina there I'm not sure what color its supposed to be.

Edited May 17, 2013 by ninjazombiemaster

[FastWoman]

My guess would be the sender. It can read exactly that way when it goes bad. (Mine did.)

[beermanpete]

I had a sender on a Ford go bad and cause the same symptom. Change the sender.

[Jennys280Z]

I drove my car for years with an oil pressure gauge that barely moved. I was letting the pros fix my car at the time and if they didn't care neither did I. After resurrecting it out of the garage after 10 years in hibernation and cleaning all the electrical connectors I could find, cleaning the sender's brought the gauge back to life somewhat (at least it moved ).

Upgrading my oil filter from the crappy orange FRAM filter to the Tough Guard FRAM filter increased the oil pressure substantially. It moved well off the zero after this. Now I'm getting the highest oil pressure I've ever seen since owning the car after doing a valve adjustment, but even still I've never seen pressure anywhere near half way up the gauge yet. Not sure if this is an issue to be concerned about or just a gauge that's reading low (that I've been led to believe is pretty common in the old Zs). I'm going to stretch the Z's legs with a highway drive this weekend. When I'm motoring along at a steady 3000 RPM instead of just going through the gears on slower roads, I'm curious what the gauge will read now.

[djwarner]

Some oil pressure senders are designed to work with idiot lights as well as gauges. Below, say 5 psi, the gauge shorts to ground to light the idiot light. Above 5 psi, it reads a resistance for a gauge. To test this, drop the engine out of gear and rev the engine up to 1500-2000 rpm. If the gauge responds, you have this kind of sender.

Now for the next question, what should oil pressure be for a warmed engine at idle. The manuals only give a spec at 2500 rpm. My gauge will do this after coming to a stop from a stretch of highway driving. Lubrication for these engines depends on oil flow rather than pressure. So if it meets the 2500 rpm spec and has proper oil level, the Datsun manual does not define a fault.