Question about the oil pressure gauges

[djwarner]

The series I 240z's came with a 140 psi gauge and a corresponding sensor (rated 10 bars - or ten times atmospheric pressure)

For the series II and later these were reduced to 90 psi and 6 bars respectively. The tech service bulletin instructed to use 10 bar sensors until the supply was exhausted. After exhausted, it instructs to use the 6 bar sensor and to replace the gauge with the 90 psi gauge.

Needless to say, very few gauges were replaced. Now with the restorations becoming more common, there are no 10 bar sensors to be found.

Considering the sensor was simply modified to use a weaker spring, is it possible that the only difference in the gauges was the 90 painted on the face in lieu of 140?

If this was the case, we could simply interpolate readings using a 0-90 scale.

Does anyone have both set of gauges to make the comparison?

[CanTechZ]

Here is a picture showing the two gauge faces side by side

 

 

This picture is from the "unique series one parts" thread:

 

http://www.classiczcars.com/topic/31737-1970-series-i-240z-unique-parts/page-3

 

I have a dash from a later series one parts car S/N HLS30 16531, it has the 90 psi gauge.  I have had the dash for over 20 years but don't know the full history, I've wondered if this was a case where the 140 psi gauge was replaced.

 

It would be interesting see the actual reading differences for both gauges with a 6 bar sending unit, this would show if interpolated readings could be used.

 

 

 

[Patcon]

I have the found the gauges to be just short of idiot lights. The one on my 73 was reading very low (close to zero) so I piped a gauge in at the oil port on the side of the engine 30 psi at idle and almost 60 when revved up.

[djwarner]

I'm curious because I've noticed a small but significant increase in the readings after my overhaul. I'd previously installed a mechanical gauge and found variations under assorted operating conditions that paralleled the OEM gauge. 

 

My main and rod bearings were worn down to the copper as expected after 186K miles but the crank journals were not scored and were to size.

 

From my past experience, I estimate I picked up 5-10 psi at 2700 rpm after changing the bearings. Also pressure loss when idling at a long, high speed run is also improved.

[Zdisease]

I have the found the gauges to be just short of idiot lights. The one on my 73 was reading very low (close to zero) so I piped a gauge in at the oil port on the side of the engine 30 psi at idle and almost 60 when revved up.

Is your add on pressure gauge connected to the oil sending unit port?

ZDisease 72 240Z

[Patcon]

Yes. I used a short nipple and added a brass tee between the sender and the block. Turned the tee up and used a piece of copper tubing to feed to the back of the gauge. I will try to post a picture at some point.