Oil pressure gauge reads too low

[histoy]

I have a '68 Coronet R/T with the Rallye gauge package.  The oil pressure gauge reads 20 lbs at idle and only 30 lbs at 2500 rpm with the engine warmed up.  I grounded the wire at the sending unit and the gauge went up to the max reading.  I then removed the sending unit and installed a direct reading gauge.  It shows 40 lbs at idle and 50 lbs at 2500.  I bought a new sending unit and it reads the 20 & 30 lbs just like the first one.  The sending unit has a small orifice.  Has anyone tried enlarging the orifice size in order to make the oil pressure gauge read higher?

[Just 6T9 CHGR]

More than likely the only solution would be to have the gauge recalibrated

[green69rt]

I have a '68 Coronet R/T with the Rallye gauge package.  The oil pressure gauge reads 20 lbs at idle and only 30 lbs at 2500 rpm with the engine warmed up.  I grounded the wire at the sending unit and the gauge went up to the max reading.  I then removed the sending unit and installed a direct reading gauge.  It shows 40 lbs at idle and 50 lbs at 2500.  I bought a new sending unit and it reads the 20 & 30 lbs just like the first one.  The sending unit has a small orifice.  Has anyone tried enlarging the orifice size in order to make the oil pressure gauge read higher?

I'd worry alot about this.  You need to find your "real" pressure and oil flow.  The oriface size should only make a difference in how fast the sensor responds, not the final reading.  Is there another way to measure the pressure and flow??  Help!!!!

[histoy]

I was afraid that the orifice size wouldn't affect the reading, but I had to ask.   Has someone tried a different sending unit on these engines that might give a more accurate reading?   I have one that is calibrated for a 100 psi gauge, but I think that one would read even lower on the 80 psi Rallye gauge.

[y3chargerrt]

You should have a 80 psi sending unit.

[histoy]

Both of my correct 80 psi sending units cause the gauge to read low compared to a mechanical gauge, so that's why I'm looking for an alternative sending unit.

[y3chargerrt]

Send the gauge out to be recalibrated. Trying to find a sending unit to make your gauge read correctly seems impossible.

[histoy]

The sad thing is that I just bought the car and it had a full restoration, including the dash and gauges.   They look great!   I think the work was done over a year ago, so I doubt they'll be covered by a warranty.  If they weren't calibrated right to begin with, I don't have much confidence that they'll come back right a second time.

[MoparMotel]

Did you ever find the problem?

I'm having the same issues... Gauge cluster restored by Redline Gauge Works, motor rebuilt with new sending unit and my oil pressure gauge reads 20 at idle and 25-30 psi driving. Checked it with a mechanical gauge and it's got like 55-65 psi.

Any ideas? I recently had to put a resistor in my temp gauge because it was reading 230 degrees while cruising, and we checked that with a mechanical gauge as well and it was only running 185.

Been trying to fix this for two years and not having any luck. Replaced the voltage regulator on the dash cluster with no change.

[A383Wing]

the OE gauges were never accurate ....no matter how hard you try to make it read right, it never will.

Best advice is to install mechanical gauges and use those are your point of reference...I would also get a mechanical water temp gauge as well

Bryan  (my opinion, consider the source)

[elacruze]

Be sure not to use teflon tape to seal the threads at the sender-that causes high resistance in the threads, altering the gauge reading. Of course, without the sealer the threads may seep. Pick your poison.

No guarantee this fixes the issue, either.

[histoy]

The car is in winter storage right now.  This Spring I'll try using a jumper wire to ground the sending unit and see if that helps.   The temp gauge had been reading too high, as well, so a resistor had to be added to the wire from the sending unit to correct that problem.

[Dans 68]

What you can do is record the actual pressure and temp (mechanical pressure gauge, thermometer in radiator), get the resistance being supplied from the transducers at those values, and adjust the gauge yourself when you are putting 5 volts and that exact resistance to the gauge (with an adjustable voltage supply and resistance board - I bought both from Amazon). Once you pull the gauge out of the dash it really is not that difficult. The high and low set points can be moved with a screwdriver. Just do it slowly.     Good luck, Jim.... 

Dan

[Charger RT]

Here is a thread on how to restore a cluster and he shows how to calibrate the gauges.
http://www.dodgecharger.com/forum/index.php/topic,37999.0.html
Tim

[histoy]

Thanks for the help guys....

[Plumcrazy]

the OE gauges were never accurate ....no matter how hard you try to make it read right, it never will.

Best advice is to install mechanical gauges and use those are your point of reference...I would also get a mechanical water temp gauge as well

Bryan  (my opinion, consider the source)

Exactly right!  These are cheap low quality gauges using 1930's technology. It is impossible to make them accurate.

[nrt69]

dont know if this will help but i had a low water and oil pressure readings for the past 20 yrs. i recently went to a new motor and electronic distributor with the ballast resistor bypassed and now it reads (seemingly) where it supposed to. im guessing my problem is with the gauges.

[gibber]

I would have to disagree on whether the gauges can be made to read accurately. I've been restoring the 66/67 Charger EL gauges for about three years now, and some B and A body gauges as well, including the 68-74 Chargers. The key is to have an accurate means of measuring resistance (I use a decade resistance box) and these gauges, IMHO, can be made to read accurately. That is of course if the insulated nichrome wire on the bimetal strip inside the gauges has not been burned due to more than 5V being applied (repeatedly). I've retested the gauges I rebuilt for my 66 Charger and after 3 years, they are still accurate. I think all your oil press gauge needs is to be recalibrated correctly. Have never been a fan of add on aftermarket gauges, that's pretty much what started me into the Mopar gauge rebuilding business..

Mark
www.thegaugedoc.com

[Plumcrazy]

I would have to disagree on whether the gauges can be made to read accurately. I've been restoring the 66/67 Charger EL gauges for about three years now, and some B and A body gauges

You can't make the oil pressure gauge read accurately.  Thermal type gauges respond far too slowly. They are okay for fuel level and coolant temperature because those values change much more slowly than oil pressure.

The most you can get out of the original oil pressure gauges in these cars is an average reading of oil pressure over the last minute or two.

Almost worthless IMHO.