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Oil Pressure Sending Unit

HanBear

By HanBear,
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HanBear Contributor

HanBear

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I've done a very thorough search and couldn't find anyone that says the exact size for the Oil Pressure Sending Unit.

I was wondering what type of thread i needed and if i can just use an autometer sending unit. Ultimately using a Autometer Oil pressure gauge?

Thank you guys!

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HanBear Contributor

HanBear

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Cool! Thank you guys. I'll give it a shot. Also I've read somewhere else that the 300zx sending unit is pretty much the same as the all the RB motors. so I'll give that a shot as well because i'm in the states and the 300zx parts are stupid easy to find! Another question on the Oil pressure though:

I live in AZ where the summer weather is 110degrees F.

I drove my car in California where the Oil pressure was FINE. but as soon as I came back to AZ (where I actually live) the oil pressure started to drop. Drop meaning almost to 0. then only getting up to maybe 20-30psi driving. Does Crazy hot weather have an effect on that?

Because in California like i said the oil pressure was fine because the weather is significantly cooler there.

I'm running 20w50 (switched today)

from 10w30

I thought since it's too hot here the viscosity is thinning out too much with 10w30 but even with 20w50 it's still dropping...

Is that a ambient heat issue? I'm going to try and replace the sending unit and if that fails too then I'm almost sure that I'm going to need a new oil pump which is going to cost me quite the bit of money because of Labor. (I don't have the time to be doing my own engine work ATM)

Thanks for your input guys!

Kinks Grand Master

Kinks

Posted
Posted

It is 1/8 bsp. Which is close to 1/8 npt so can work.

Yikes. Not on my car thanks. Thread pitch and included angle are both different!

http://pipeandhose.com/?q=node%2F2

The "force to screw it in" that 89CAL mentions is because the threads are binding. It's close enough to "work" - whatever that means.. but you will have a large amount of force on the 2 threads that are binding and the other threads are sitting there doing nothing. It won't be kind to either thread either.

Spot the engineer huh :P

Hanbear the 300ZX should have a water/oil heat exchanger.. primarily this heats the oil quickly to operating temp ~85C but it also means the oil shouldn't get too much hotter than that unless you're on a racetrack. 20W50 is extremely thick oil, are you using mineral or full synthetic? I only use full synthetic 5W40.

You need to state oil pressure as a function of RPM as well. For example my car gets about 2 bar (30psi) at idle and then 3-4 bar at 3000RPM once fully warmed up (driving for at least 30 minutes). My last car showed less. The standard gauges CAN be unreliable so if you suspect issues it's best to use a good quality aftermarket gauge.

Ben C34 Grand Master

Ben C34

Posted
Posted

Just to clarify there's no way I would do it or reccomend it.

I added that quickly as I have posted in previous threads on this topic and someone always comes along and says they use npt no worries.

So. To clarify. A 1/8npt male thread will fit into the 1/8 bsp female thread, poorly.

89CAL Grand Master

89CAL

Posted
Posted

Yikes. Not on my car thanks. Thread pitch and included angle are both different!

http://pipeandhose.com/?q=node%2F2

The "force to screw it in" that 89CAL mentions is because the threads are binding. It's close enough to "work" - whatever that means.. but you will have a large amount of force on the 2 threads that are binding and the other threads are sitting there doing nothing. It won't be kind to either thread either.

Spot the engineer huh :P

Hanbear the 300ZX should have a water/oil heat exchanger.. primarily this heats the oil quickly to operating temp ~85C but it also means the oil shouldn't get too much hotter than that unless you're on a racetrack. 20W50 is extremely thick oil, are you using mineral or full synthetic? I only use full synthetic 5W40.

You need to state oil pressure as a function of RPM as well. For example my car gets about 2 bar (30psi) at idle and then 3-4 bar at 3000RPM once fully warmed up (driving for at least 30 minutes). My last car showed less. The standard gauges CAN be unreliable so if you suspect issues it's best to use a good quality aftermarket gauge.

I said i needed to force it in to get it in not that i actually forced it in

I worked out it wasnt 1/8NPT then made a plan to get around this. So now i have the right fitting in the block to a braided line to an oil manifold for my sensors

HanBear Contributor

HanBear

Posted
  • Author
Posted

Yikes. Not on my car thanks. Thread pitch and included angle are both different!

http://pipeandhose.com/?q=node%2F2

The "force to screw it in" that 89CAL mentions is because the threads are binding. It's close enough to "work" - whatever that means.. but you will have a large amount of force on the 2 threads that are binding and the other threads are sitting there doing nothing. It won't be kind to either thread either.

Spot the engineer huh :P

Hanbear the 300ZX should have a water/oil heat exchanger.. primarily this heats the oil quickly to operating temp ~85C but it also means the oil shouldn't get too much hotter than that unless you're on a racetrack. 20W50 is extremely thick oil, are you using mineral or full synthetic? I only use full synthetic 5W40.

You need to state oil pressure as a function of RPM as well. For example my car gets about 2 bar (30psi) at idle and then 3-4 bar at 3000RPM once fully warmed up (driving for at least 30 minutes). My last car showed less. The standard gauges CAN be unreliable so if you suspect issues it's best to use a good quality aftermarket gauge

I'm only using the z32 Oil Sending Unit because it fits the RB series engines.

As far as the Oil pressure goes. In cool weather it operates fine. I think the standard pressure guage is in Bar increments of 2 right? 0 - 4 - 8?

If it is then here's what it's doing:

Cool weather cold start jumps to 4 then warm goes back down to about 2. and driving goes to 4.

The weather here in AZ it would operate fine when i first start the car for the day. Then I'll drive around and the pressure would go down to below the 2 at idle and then would jump to between 2 and 4 so around 3 driving. Sometimes it'll be at 2.

So I thought that since I'm driving in 110-120 degree F weather the oil is just cooking and thinning out. It's still doing this with the 20w50 in there. :(

I'm HOPING that the sending unit and Oil Cooler will get the job done with a new oil pressure gauge. If not then I know it's my pump or gap between the bearings... which will ask for a Engine Pull.... :(

I'm just hoping.... wish me luck Lol

Kinks Grand Master

Kinks

Posted
Posted

yeah the standard gauge is kg/cm^2 which is almost identical to bar (there is a 2% difference which can be safely ignored).

the standard gauges are known to be quite inaccurate. from "not bad" to "substantially wrong" depending on your luck :)

my R33 used to idle at 2 bar but when the oil was close to changing would sometimes drop to 1 bar (or less) at idle and only 2 bar while driving (~3000RPM). certain brands of oil showed this characteristic more, some less. I suspect the gauge was overly sensitive around the lower end of the scale TBH

never had a problem with the motor though, I drove it like that for over 100,000km :) so I don't think you need to panic about engine pulls just yet. Get an aftermarket gauge on it just for peace of mind though.

ALL oils lose pressure when they warm up - they get less viscous which means less resistance to flow. Synthetic oils are naturally better at maintaining viscocity when hot, that (and their superior lubricating ability) is why we all recommend them.

HanBear Contributor

HanBear

Posted
  • Author
Posted

Well thank you all for your inputs! I replaced the sending unit with a z32 sending unit today. The oil pressure is holding steady and fine. Luckily for me. Haha. So far.... I haven't driven too much on it but I'll see how it goes. So far it seems that the only thing wrong was my sending unit. Haha. Thanks again y'all!!!

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