Oil Pressure Sending Unit Problems

[z3beemer]

On one the first starts on my 73 restoration project, I notice I didn't have any oil pressure showing on the gauge.  I was pretty sure I had oil pressure because the engine wasn't making a lot of noise but shut it down just to be on the safe side. Using the forum, I was able to find out how to check  to determine whether it was the gauge or the sending unit.  Turns out it was the sending unit.  I ordered a new one from Zcar Depot.  I installed it and that took care of the issue. I started noticing a small oil leak under the car. I had a hard time locating the source but finally discovered it was coming from the oil pressure sending unit. It appeared dry around threads, but i removed it and sealed around the threads with permatex and reinstalled, still leaked, still dry around the threads, tried again using teflon tape, seemed to get worse but still dry around the threads. So i removed it again and figured it may be leaking around the back seam where the front and back portions of the unit come together. I did notice some oil there. On the bench, I injected some air into the unit and quite a bit of oil came out around the seam. I notified the guys at Zcar Depot and they were very accommodating (as usual) and sent me out a replacement.  The first one they sent me was silver and screwed into the block  very easily. I was able to get 3 or 4 turns on it before having to use a wrench.  The second one was a Beck/Arnley brand and gold in color. I had a hard time getting it started in to the block and when I did I could only get about 1/2 turn on it and it was very tight. Here's what I did.  The threads appeared to be 1/8"-27 NPT thread.  I ran a tap in the hole in the block.  It threaded in smoothly without the use of any tools.  Then I ran a die of the same size on the threaded side of the sending unit.  It took a little more effort but nothing excessive. I then buffed the threads on a wire wheel to remove any of the gold plated coating.  I was now able to start it into the block hole about one turn or so.  Using a wrench I would turn it one turn at a time then back it out, it was still pretty snug but seemed to be going in smooth and straight.  I did this 4 or 5 times, turning it in a little deeper each time until it felt like it bottomed out (or was in as far as it would go).  That took care of the problem andi the leak.  I thought this info may be helpful in case others run into the same issues. The attached pic shows where the oil was leaking out once I applied air pressure to it.

[dutchzcarguy]

11 hours ago, z3beemer said:

I then buffed the threads on a wire wheel to remove any of the gold plated coating. 

I hope you did this in a "well ventilated room" as the "gold" is a metal called... Cadmium.. it it very poisonous/toxic!  (the proces to get it on there is called passifying) 

There a lots of passified parts on our cars..

When installing a oilpressure sender it's no problem to use some P.T.F.E tape also called teflon tape on the thread, to keep it from leaking.  Personally i never have seen a o.p.s. that was leaking in the way you described.

[dutchzcarguy]

11 hours ago, z3beemer said:

The threads appeared to be 1/8"-27 NPT thread.  I ran a tap in the hole in the block. 

I understand that the thread was already 1/8"-27 NPT  as the tap needed no force to go through the thread?

You DID alter the thread on the sensor, i think that's the way to go!  If this connection is gonna leak (As there are now 2 sorts of threads on it.. sort of..) you use some tape as sayd..  (also.. I just remember..  i think the thread on there was tapered? .. so i think as you went further on to the thread it was more difficult to cut the thread?)  anyway use some PTFE. (always put it on stretching the tape and go with the thread, not against it. 2-3 turns is enough.)

[HS30-H]

43 minutes ago, dutchzcarguy said:

I hope you did this in a "well ventilated room" as the "gold" is a metal called... Cadmium.. it it very poisonous/toxic!  (the proces to get it on there is called passifying) 

In fact there was little to no Cadmium plating on these cars. By the late 1960s the use of Cadmium plating in the Japanese domestic automotive and motorcycle industries was being severely restricted, for obvious reasons.

Nissan used Zinc ('亜鉛' = 'Aen') plating to protect most of the steel parts on the S30-series Z, either with a 'Clear' (sometimes called 'Blue') passivated finish or a Gold (also called 'Yellow') passivated finish. The Gold passivate is Hexavalent Chromium.

[Patcon]

1 hour ago, HS30-H said:

The Gold passivate is Hexavalent Chromium.

What parts would have received this treatment?

[dutchzcarguy]

2 hours ago, HS30-H said:

there was little to no Cadmium plating on these cars.

Good news/info!  👍  Happy to hear.. i guess i heard people telling about it.. calling it a cadmium finish but in reality it's zinc..

So these new plated parts are in Hexavalent chromium..  Am (again) learning something today! 🙂

 

EDIT EDIT EDIT  !!!!

EDIT.. as you said not all is chromium6..  i looked at the website of the firm that did my parts and they say it's zinc passified in blue or yellow.

so NO chromium6 on my cars!  😅

 

 

Tip.. put a small steel strip in the springs.. now you get a nice perfect passified part..

 

 

Edited July 3, 2023 by dutchzcarguy

[dutchzcarguy]

Just looked it up.. but hexavalent chromium.. isn't much better.. i remember there were a lot of sick service engineers in the Dutch railways (NS) because of it.. we call it chromium6 and it's very bad stuff.. (when taking of paint and layers.. you need an awful lot of protection..)

Read this also:  What is Hexavalent Chromium (or Chromium-6)? | Britannica

[dutchzcarguy]

Also..

Hexavalent chromium - Wikipedia

 

[HS30-H]

1 hour ago, Patcon said:

What parts would have received this treatment?

Pretty much all 'gold'/'yellow' finish plated parts on Nissan cars.

[HS30-H]

1 hour ago, dutchzcarguy said:

EDIT.. as you said not all is chromium6..  i looked at the website of the firm that did my parts and they say it's zinc passified in blue or yellow.

so NO chromium6 on my cars!  😅

I'd be interested to hear what process/chemicals the company which re-plated your parts used to put a passivate coating on your zinc-plated parts. If it isn't Hexavalent Chromium, what is it?

1 hour ago, dutchzcarguy said:

Good news/info!  👍  Happy to hear.. i guess i heard people telling about it.. calling it a cadmium finish but in reality it's zinc..

I think it's just old habits/assumptions dying hard. Yes, Cadmium plating used to be common on auto/moto parts (British motorcycles used to be covered in the stuff), but Nissan - along with most of the other Japanese manufacturers - found alternatives from the 1960s, largely prompted by national health scandals involving Cadmium being leaked into water supplies. There were instances of several other poisons being leaked long term, such as that which caused the Minamata Disease scandal (Methyl Mercury). Really horrible.    

[CanTechZ]

Actually the OEM oil pressure sending units used by Nissan are 1/8"-28 BSPT, not 1/8"-27 NPT. If your Beck-Arnley was 1/8"-27 NPT that would explain why it would not screw in easily. Here are pictures fitting my thread pitch gage into an old OE sending unit I have, The 28 threads per inch gage fits well (first pic) and the 27 did not.

 

 

 

 

In addition to thread pitch differences, the NPT thread also has a slightly larger nominal male thread diameter. the chart below is from Swagelok, BSPT is also known as ISO 7/1

Edited July 3, 2023 by CanTechZ

[dutchzcarguy]

AND... as it's thread is tapered, you don't need to screw it all the way in.. as a matter a fact about half way is enough and some tape (PTFE) is a good insurance that you don't brake it.

 

18 hours ago, HS30-H said:

I'd be interested to hear what process/chemicals the company which re-plated your parts used to put a passivate coating on your zinc-plated parts. If it isn't Hexavalent Chromium, what is it?

It's a mistery to me what they used. But they say it's zinc.. colored blue or yellow..

I can give you theire website. but i have to say: they only did my parts because i bring and get them myself and they do them between the other (Very big) orders..  Last time he said they normally don't do these small (private) collections of parts.

GTO Plating BV – Passie voor Perfectie     (It says: we have passion for perfection.)