Datsun Roadster Forum-311s.org

My stock electric oil pressure gauge died. It was reading up to maybe 20psi on rev and of course like most barely moved above zero at idle. Replaced it with a working gauge. Now I have 40psi at idle. That's not right per specs, well maybe. It was a U20 pump. AS a note here I went through 4 new senders to get one that worked. What a waste of money.

So I put in a VDO electric gauge with correct sender and get 50psi at idle and 75 at rev. Whoa, really not right. Next mechanical gauge and 50 and 75. So with help it was determined the relief valve must be stuck.

So out with it and in with a new H20 pump. First start for a few seconds with engine cold 50 and 75. So since the pump has been sitting for I don't know how many years I warmed the car up thoroughly and I get 25psi and 50psi with 20-50 oil. Relief valve must have been gummed up.

So I switch it to 10-30 and still get about 25 and 50. What are you people getting with stock or aftermarket mechanical gauges in a 1600? Thanks.

Curtis: My ‘69 1600 w/stock mech. gauge running non-synthetic 10w-40, barely registers 5-7 psi (approx) at idle when fully warmed up (20-30 mins of driving). Under load (hot), it runs just above half way on the gauge (about 45 psi) as soon as you give it any gas and then stays there (+/-5 psi) while driving.

So, under load, 45-50 psi is what I normally see hot. I wouldn’t put too much faith in the hot idle accuracy of 5-7 psi though as that also reads 15-20 psi at idle when cold.

So, long ago I temporarily plumbed in a mechanical oil gauge to make sure I had pressure as my stock one always read low and confirmed I had plenty of pressure (Sorry don't remember what, but it was fine). I just installed a replacement sender I had as my old one leaked, and the new one reads even lower. I sure would like to have an oil pressure gauge that actually works. There are many similar looking ones out there. New ones for our car run $120+, while others for cars are $25 or so. Given that my stock one already read low I'm a bit hesitant to order one for $120. I already know the 240z one does not work... anyone know HOW these senders work and if they can be somehow calibrated or Identified? I know I can run a mechanical one but don't really want to replace the stock unit.

Here it is. There seems to be an adjustment inside they use when made which you cannot get to. Mechanical type sender.

Being challenged regarding such things, I would assume that there is some kind of diaphragm inside that moves back and forth based on pressure that moves an electrical connection to and fro that changes resistance to create a signal to the gauge? Kinda like the gas tank float sensor? If so I would assume that resistance can be measured by a multimeter? I'm envisioning some way of testing a known good sending unit, identifying parameters, and trying to find a decent replacement or a means by which to adjust one. My knowledge of such things is very basic, I barely know how to use a multimeter (!), but that's never stopped me!

Given that you (Curtis) tried several senders before getting a good one, you can see my hesitation and desire to get this right. My "newer" sender, while it does not leak so my engine is cleaner, reads zero most of the time.

So I hooked up all three senders to my meter set to ohms and measured resistance between the post and the unit, then put air pressure to it. My leaky original had 19.4 and went to 20.4... not much change. The 240z one was much more responsive and consistent with a starting resistance of 84.5 and dropping to 21 with near 100lbs of air pressure, and would show a gradual increase in resistance with a drop in pressure as one would expect. The other "Roadster" one I have started with 57.4, but increased to 65.4 or so for a moment, but then stopped responding at all and ended up staying at 57.4 regardless... broken now? It was reading zero at speed the other day and a few lbs when the engine was cold and idling. I re-installed it but I didn't try it yet.

So, based on this very limited test, it seems the Roadster ones work backwards from the Z, and neither of the two I have appear trustworthy. Anyone care to test some they have sitting around? Takes an air compressor, some rubber hose and a multimeter. Maybe someone with a known good sender can test it and post what they find... if this test even tells us anything...

Hello! I did a write-up on the electric oil guage sender: Oil pressure really low (part2), dated June 4,2020. It explains the workings of the sender, and what i did to correct it (was bored during covid shutdown, thought I would give it a try). Just a follow up- unit still works fine, no leaks at all. Any other questions, I'll try to help.

Erock311 wrote: ↑Wed May 25, 2022 12:40 pm Hello! I did a write-up on the electric oil guage sender: Oil pressure really low (part2), dated June 4,2020. It explains the workings of the sender, and what i did to correct it (was bored during covid shutdown, thought I would give it a try). Just a follow up- unit still works fine, no leaks at all. Any other questions, I'll try to help.

Link to post or document?

Curtis wrote: ↑Wed May 25, 2022 12:54 pm

Erock311 wrote: ↑Wed May 25, 2022 12:40 pm Hello! I did a write-up on the electric oil guage sender: Oil pressure really low (part2), dated June 4,2020. It explains the workings of the sender, and what i did to correct it (was bored during covid shutdown, thought I would give it a try). Just a follow up- unit still works fine, no leaks at all. Any other questions, I'll try to help.

Link to post or document?

viewtopic.php?p=308232#p308232

Well... guess I can say "Thank you" Again! Obviously I saw this, but clearly had forgotten about it... probably had decided to move on from the issue, only to have it come back to my attention again from trying to stop an oil leak with my original sensor. So, yes, pics if you have them would be great! Mine already leaks but I hope to have it seal up again, so I may be inquiring about the seal. I'll read through your post again and dig into mine... THANKS!

It looks like the hole is there for adjustment

The PSI saga continues. I pulled the engine to address a transmission leak and the high psi. The U20 pump as noted before was running up to 75 psi and was thought to have a failed relief valve problem. In went a new H20 pump I had had for a few years. Just as high at first and then came down to a high of about 60 at rev.

I had to pull the engine again. So I took two R16 relief valves and two H20 one of which I had just received apart. I compared the strength of the springs. The H20 spring from the pump I had put in the car was 50 percent stronger than the three other springs. So I put the original R16 pump in that I had taken out to put in the U20 pump. Finally went for a short drive yesterday. At startup I was getting 40 psi at idle and 60 plus at rev. When I got back it settled down to as low as 25 psi at idle. Still goes on up towards 60 at rev but I can live with that.

One conclusion from this is stock gauges are crap. I tested four gauges I had on the bench with different resistor loads and none of them were the same.

Again, I would politely suggest, and / or request, input from Jon Frampton,...our Forum "Go To Guy for all things, gauges"..." on this forum,...to weigh in on this issue,....
Jon,...are you "Out There Buddy" ?
Respectfully, Mike (a gauge "Frampton, Restored Gauge Set" customer....

Bringing this back up....does anyone have a follow up on OPS's? Also, has anyone found a mechanical gauge that will fit in dash, look decent and somewhat stock?

I put the mechanical gauge in and the pressure settled down after a while. I changed to 10-30 I think and it was still high at first then went down after some driving. I have 25 to 35 at idle and about 50 at rev. Works for me.

I plan to have the stock gauge converted to mechanical.
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