Series I oil pressure sender question

[djwarner]

My Series I has the original 140psig gauge and the sender was leaking when I bought the car. A trip to the local auto supply store sourced a compatible (?) sender.

Later I found out that the original sender part number was superseded with the same part number as the ones found on Series II and later cars.

Still later, I found out that the shop instructions state to also replace the gauge with a 90psig when replacing with the superseded sender. This makes sense for the then modern model car, but sucks when trying to restore a 43 year old car and desire to keep the original gauge.

From what I can tell, the original sender was a 10 Bar sender (10 atmospheres or 145psig) and the replacement sender is a 6 Bar sender (87 psig).

So what readings do I get when I use a 6 Bar sender and a 10 Bar gauge?

I did find a modern 6 bar sender that had the following specs:

6-8psig open circuit (this explains why our gauges go to zero when idling after a hot run).

15 psig - 50-79 ohms,

70 psig - 10-30 ohms,

90 psig - 8-22 ohms.

I have no idea what the original sender specs were, but the 6 Bar specs seem pretty loose.

Does any one have specs for the 10 Bar sender?

Or better yet, does anyone know of a suitable sender from a different model/make?

[CanTechZ]

I replaced my series I oil sending unit PN 25070-89910 in 1979 with the correct 10 KG OEM switch and it stills seems to read OK on the 140 psi gauge. Attached is a parts page showing different PN's for the 10 KG and 6 KG units. Is there a date on shop instructions sheet that you have? Sorry I don't have any specs for the 10 KG sender.

Mike

[djwarner]

Hey Mike,

I double checked with Courtesy Nissan and that part number was discontinued by Nissan as I was told.

[CanTechZ]

Sorry about that, good luck on your search on an NOS part, maybe you will get lucky. I did a quick search and saw this on ebay, no idea if this is a good vendor:

Vintage Nissan Oil Pressure Sender Part Number 25070 89910 | eBay

Sorry, just noticed it was an old auction, but at least they do come up, cheers.

Edited August 25, 2014 by CanTechZ

[AZ-240z]

Hello dj,

This may, or may not help, but here is what I have found in trying to understand the inherently low pressure readings on series 1 cars.

Here is what Wick Humble in his book "How to Restore Your Datsun Z-Car" had to say. By the way, this low pressure reading is, indeed,

inherent to our early cars as this low pressure anomaly was present the day I drove it off the lot with zero miles on the clock.

My car has the 140 psi gage and the 25070-89910 10kg sender switch. I asked my mechanic to check my oil pressure with

his mechanical gage and these were the reading:

Idle - 22 psi

3500 RPM - 64 psi

My stock 140 psi gage and 25070 - 89910 sender the reading are:

Idle - 0 psi

3500 RPM - 35 to 40 psi

My car is 100% stock with a pretty tight engine with approximately 5M miles on it. My compression readings are 167, 166, 168,

176, 167, & 175 for cylinders 1 thru 6 respectively.

I have peace of mind knowing that zero psi really means at least 22 psi as everything on my car will always remain factory stock.

I also know that many mechanics, to give owners peace of mind, would install a roadster sender which will always give a

positive reading. I used one for a time, but don't remember what the specific readings were except that it was always positive.

I hope this helps in your quest for a sender.

Dan

[djwarner]

Thanks Dan,

Your attachment confirms what I have found.

I was hoping someone found a 10 Bar sender from a different application that would work.

Many modern senders appear to be voltage based rather than current based, so finding a substitute sensor may be problematic. I will probably rig up a 500 ohm pot to simulate a sender to extract a set of specs for my search.

[grannyknot]

dj, please update if you find anything, I know I have a tight engine but that 0 reading on the gauge always catches my eye.

Thanks,

Chris

[jfa.series1]

I was surfing the Banzai Motorworks site today and noticed Mike has one in his catalog that is advertised as "correct". It might be worth checking with him.

[djwarner]

Thanks for the heads up Jim. He states the unit he has is for 70-76 models and is probably the 6 bar unit as the 10 bar unit was only used in the 69-70 production.

I made some tests on the gauge. It appears to be looking for:

0 psi - 83 ohms

25 psi - 60 ohms

50 psi - 40 ohms

90 psi - 24 ohms

A note to anyone trying this, the water temp/oil pressure gauge has an internal voltage regulator that is a bi-metal mechanical type that is to slow for our digital meters.

[kats]

On 8/26/2014 at 4:14 AM, AZ-240z said:

Hello dj,

This may, or may not help, but here is what I have found in trying to understand the inherently low pressure readings on series 1 cars.

Here is what Wick Humble in his book "How to Restore Your Datsun Z-Car" had to say. By the way, this low pressure reading is, indeed,

inherent to our early cars as this low pressure anomaly was present the day I drove it off the lot with zero miles on the clock.

My car has the 140 psi gage and the 25070-89910 10kg sender switch. I asked my mechanic to check my oil pressure with

his mechanical gage and these were the reading:

Idle - 22 psi

3500 RPM - 64 psi

My stock 140 psi gage and 25070 - 89910 sender the reading are:

Idle - 0 psi

3500 RPM - 35 to 40 psi

My car is 100% stock with a pretty tight engine with approximately 5M miles on it. My compression readings are 167, 166, 168,

176, 167, & 175 for cylinders 1 thru 6 respectively.

I have peace of mind knowing that zero psi really means at least 22 psi as everything on my car will always remain factory stock.

I also know that many mechanics, to give owners peace of mind, would install a roadster sender which will always give a

positive reading. I used one for a time, but don't remember what the specific readings were except that it was always positive.

I hope this helps in your quest for a sender.

Dan

Hi Dan , your  data helps everyone a lot  , I was also wondering too about the low readings of the oil pressure. My first Z is a 1972 240Z when I was living in Bakers Field CA which always showing middle in the gauge. Then I bought a 1970 240Z , it always stayed very low in the gauge.

I remember I was reading Mr. Wick Humble ‘s book and learned  my 1970 car was not wrong .

Here are pictures which were taken recently, my 1970 Z432 ( shared with all the other S30 DOM & EXPORT using the same 10kg switch , 10kg scale ) and 1970 Datsun 240Z , And 1972 Fairlady 240ZG ( 6kg switch with 6kg scale ) .

Just for your reference.

By the way , 25070-89910 ( 10kg ) switch is now approximately 200-400 USD if it is a new , S20 owners are seriously want it . 

Looking at my Z432 , S20 might able to be said it’s oil pressure relatively higher than L -series engine , what do you think of it. 

Kats

[kats]

I forgot to put this , my 1972( 12/71 made ) Datsun 240Z . I think a 6kg switch cooperated with a 6kg / 90lb scale work pretty good, it makes me feel happy .

Kats

[240260280]

TSB from 1973 Issue.

 

 

Here is 140psi Sender:

 

Edited August 25, 2019 by 240260280