oil pressure gauge question

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dan5354

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I have an oil pressure gauge that when I ground the sending unit wire it makes the gauge head up towards the top quickly, but when hooked up to the sending unit it barely registers. I bought a new sending unit and it does the same. Is it possible that I got a bad sending unit or is there something else that can cause this condition? Thanks in advance
 
Yes, the gauge itself can be off. The grounding of the wire is just an indicator, not an accurate test.

If you know what a resistor is, get a 22 ohm resistor and put it between the oil pressure sender wire and ground, and turn the key to RUN. The gauge should read about halfway.

Did you buy a sender specifically for this car?

Do your temp and fuel gauges read OK? If they read low too, then the problem may be in the voltage limiter.
 
dan5354 said:
I have an oil pressure gauge that when I ground the sending unit wire it makes the gauge head up towards the top quickly,
Click to expand...

That does not mean the gauge working like it should, from my experience. Is it factory oil pressure gauge?

Test with mechanical oil pressure gauge, you will know exactly what happen.
 
You can get an idea what the gauge might be doing by both checking the others and by subbing resistors at the sender wire. It's possible a bad terminal in the bulkhead connector. Be sure you are asking for the correct sender application. they are not "universal."

Resistor values / vs gauge reading. Fuel, temp, oil, all samo If all three are off, could be bad gauges, bad connections, or more likely the instrument limiter. Yours with a Rally dash is in the fuel gauge. INSIDE

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)
 
Mine is the same way, but it does work to some degree. Thanks for the info guys. I'm happy the gauge moves at all. Fortunately, my Temp and Fuel gauge work much better.
 
The terminal on the oil pressure sender could come off and short to ground, especially on the small blocks. Feckin with the distributor would get the terminal knocked off the sender. Takes only 3 to 5 minutes for zero resistance to damage the gauge.
That scenario or simply low oil pressure is my best guess.
 
Thanks for all the info. I think with mine the oil pressure gauge got too much voltage at one point, but then I thought since the gauge pegged that it was o.k.. I'll try the resistor at the sending unit wire just to be sure. My gas and temp work good and I have put in a solid state limiter, so that rules that stuff out. I was wondering if a gauge could get ruined without totally frying it?
 
You should attach a manual oil pressure gauge to assure you actually have adequate oil pressure.
 
You do have a ground strap from the engine to the firewall? Also a good idea to have one from battery negative to chassis as well.
 
dan5354 said:
I was wondering if a gauge could get ruined without totally frying it?
Click to expand...
Yes, I recently went through this with a fellow over on FBBO with a fuel gauge, and the gauge was damaged and not registering correctly. A different gauge worked fine with the same sender and limiter.

If you have one of the solid state limiters (not the RTE one), then check the voltage to be sure it is at a steady 5v. The RTE limiter supposedly pulses like the original limiter so is harder to check.

An issue with a firewall-to-engine strap is not likely if the temp gauge registers correctly; the temp sensor and oil pressure sensor both ground via the block. So if one is good, they both should be good.

BTW, some nut on here is advocating the practical step of attaching a manual oil pressure gauge to see what the oil pressure really is..... something about seeing if you really have good oil pressure.... where does he get such ideas? LOL
 
In case this info helps, I had all my gauges rebuilt and the electronic limiter installed plus, I bought a new sending unit and cleaned my bulkhead connectors. My oil pressure gauge only goes up to the second line when cold and down a bit once warm on 3 different engines a rebuilt Slant 6, a tired 5.9 Magnum and a new 408 Stoker Magnum. The Temp gauge has always been just below half way once warm. Fuel gauge is pretty darn accurate and has a fresh 1/2" sending unit and tank.

One of these days I'll have time to put in my Vintage Air Gen V, my console with an aftermarket shifter in place of the stock shifter and an aftermarket oil, temp and volt gauge. Yes, I did the Amp gauge bypass. These three items end up in pretty close proximity to each other under the dash, which is why the Aftermarket gauges are not in yet.

My Factory Mopar OBD II ECU does monitor both oil pressure and water temperature to some degree too, but I do want to augment engine vitals monitoring with some analog gauges as soon as I have some spare time.
 
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