Testing oil pressure sender.

[Wade]

Any advice to check oil pressure using a meter on the sender? What type of reading would I be looking for. My gauge is not working atm for whatever reason and I just started back up working on the Z after a few years, want to make sure my readings are ok. 71 240z gauge, but it has an L28 with existing pressure sender, I read that the readings will not match up with it being different settings. Ill look into that, just atm Im not getting any reading at gauge.

[Z train]

Ohm meter.Check the sender with the engine off (key on-duh)then with it running.There should be a difference which would be listed in the FSM.

[timhypo]

Reading his post, I think he wanted to know if there was a way to plug a multimeter into the sender and determine his oil pressure, not a way to test his guage/sender...

[MikeW]

Reading his post, I think he wanted to know if there was a way to plug a multimeter into the sender and determine his oil pressure, not a way to test his guage/sender...

I don't see the difference. The sender is a simple device that varies resistance with oil pressure. If the sender indicates no oil pressure it's likely a bad sender but could also mean there's truly no oil pressure. Assuming the sender is working and is accurate (which they're not) you would be able to calculate the oil pressure just using a multimeter on the sender if you know the proper formula. After all, that's what the oil pressure gauge is doing with the same input.

[Wade]

Hooking a meter directly up to the sender and taking a reading from there. The sender works, but the needle in my gauge is broke. Like Mike said, if anyone knows that formula or something close to it to give me a general idea. Thanks.

Edited July 31, 2010 by Wade

[beandip]

To eliminate the guess work , I just bought a inexpensive mechanical oil pressure gage . $15.00. Removed the sender and screwed in the supply line. My old sender told me that at Idle I had next to zero pressure , but in reality 25 lbs and at 2K RPM 50 lbs. So I replaced the old sender and now I can determine what my gage is really ''saying''. They are not known to be right on accurate , but just an indicator to what is going on.

My 2cts Gary

[wa5ngp]

On my '73z when the engine is off the sending unit measures infinity ohms. If someone had told me this I would not have believed them but that's what I measured. This is with the sending unit disconnected of course.

At idle the resistance goes to about 50 ohms and then when I rev up to like 2k it drops to about 30 ohms.

these gauges are very slow in responding since the meters themselves utilize heating of bimetalic strips to drive the indicator. Furthermore, the voltage regulator circuit for these gauges consists of pulses of voltages again from heating of bimetalic strips.

If you measure the resistance of your gauge with the motor running be sure to connect the ground lead of your ohmeter back to your battery. If you connect it to the alternator ground terminal you may get a wierd reading due to the high charging amperage that can cause a ground bounce on the alternator.

To confuse matters more, don't use a digital meter. When I tried mine it indicated nothing at all. Apparently there is enough electrical noise from spark plugs etc that the dvm got confused.

I remember 25 years ago in the winter panicking when the oil pressure showed zero. I had to remove the sending unit and clean it out with kerosene as some sludge had blocked it off.

I did the same thing you did. I got a cheapo mech oil pressure gauge just to double check that I really did have oil pressure.

Right now, I use a T fitting so I can connect up the sending unit and a switch. The switch is to turn off the electric fuel pump in event of no oil pressure in case of a crash.

Don

[beandip]

To eliminate the guess work , I just bought a inexpensive mechanical oil pressure gage . $15.00. Removed the sender and screwed in the supply line. My old sender told me that at Idle I had next to zero pressure , but in reality 25 lbs and at 2K RPM 50 lbs. So I replaced the old sender and now I can determine what my gage is really ''saying''. They are not known to be right on accurate , but just an indicator to what is going on.

My 2cts Gary

I forgot to mention that my oil pump is a turbo pump. The relief valve activates at 70 PSI on these engines and when the oil is cold it will go to that point and relieve. Another reason to warm you engine in the morning. So if you notice the needle on your gage stop between mid and the extreme right . That is the relief valve opening.

[Zdisease]

On 7/31/2010 at 2:44 PM, beandip said:

To eliminate the guess work , I just bought a inexpensive mechanical oil pressure gage . $15.00. Removed the sender and screwed in the supply line. My old sender told me that at Idle I had next to zero pressure , but in reality 25 lbs and at 2K RPM 50 lbs. So I replaced the old sender and now I can determine what my gage is really ''saying''. They are not known to be right on accurate , but just an indicator to what is going on.

My 2cts Gary

Where did you purchase the Oil Pressure Gauge?

[S30Driver]

Easy to find,  such as this one on Amazon.   $20

https://www.amazon.com/Sunpro-CP8206-StyleLine-Mechanical-Pressure/dp/B00029K00Y/ref=sr_1_20?keywords=Mechanical+Oil+Pressure+Gauge&qid=1559132417&s=automotive&sr=1-20

[Dave WM]

getting the threads right may be a challenge. I took tire pressure gauge (the round kind that you just push on and read) got it from autozone or harbor freight IIRC, removed the little chrome part, cut off the part that pushes on the valve stem, then used a file to taper the threads a touch. Clean up all the filings of course, it would thread on the block, not a perfect seal just enough threads to hold on, but enough to get a reading of about 40lbs on a cold engine startup. I just wanted to check the calibration of the sending unit.

Edited May 29, 2019 by Dave WM

[Zdisease]

On 5/29/2019 at 6:29 AM, S30Driver said:

Easy to find,  such as this one on Amazon.   $20

https://www.amazon.com/Sunpro-CP8206-StyleLine-Mechanical-Pressure/dp/B00029K00Y/ref=sr_1_20?keywords=Mechanical+Oil+Pressure+Gauge&qid=1559132417&s=automotive&sr=1-20

Need to order the Metric adapters also.  Hardware delivered with gauge caused me to reinstall sending unit.