My classic instruments oil pressure sending unit is giving me fits! I have teed in a mechanical gauge so I know the oil pressure is good, when the engine is cold the classic instruments gauge reads 90 PSI, the mechanical gauge reads 60 PSI. After warming up the classic instruments gauge will begin fluctuating from 0 to 70 #'s, sometimes sitting at 0 for 10-15 minutes at 2800 rpm and as soon as I let off the gas pedal it will jump to 60PSI, stay there for awhile and then fall back to 0. I bought the original unit from Summit and have since replaced it 2 more times all with the same result. I've talked with Classic and about the only thing they've offered is that they changed manufactures for the sending unit and wonder if the resistance wire is giving problems, no other suggestions. I thought maybe I was having a problem with the ground so ran a separate ground wire to the unit, still same problems. I should mention I replaced a dolphin gauge and sending unit with the classic instruments gauge, the dolphin unit lasted 8 years with no problems before I accidently cracked the gauge cover. I can always go back to the Dolphin gauge but it bugs me I spent the money on the classic instruments unit and can't get it to work. Appreciate any thoughts.
Did you use Teflon tape installing it? That's the problem if so. This is from their website. With mechanical gauge and ohmmeter you can verify readings: Classic Instruments’ 100-psi oil pressure gauges register 0 psi at 240 ohms resistance, 50 psi at 105 ohms resistance, and 100 psi at ~33 ohms resistance (the lower the resistance, the higher the psi reading). Classic Instruments’ SN52 (100 psi) oil pressure sender works in a resistance range of 240 ohms at 0 psi to 33 ohms at 100 psi. SN54 (80 psi) oil pressure sender works in a resistance range of 240 ohms at 0 psi to ~33 ohms at 80 psi. The Classic Instruments’ oil pressure sender gets a ground connection through the mounting threads. Without a proper ground to the sender, the gauges will read low or peg below 0 psi. Pipe sealer should be used sparingly on the threads of the sender and Teflon tape should not be used. Sent from my SM-S320VL using Tapatalk
No Teflon tape, tried grounding sender directly with no change. Can’t figure out why it only happens when hot. Sent from my iPhone using H.A.M.B.
Can’t find a mechanical gauge that matches the rest of the gauges. Sent from my iPhone using H.A.M.B.
Because what ever moves inside the sender is not moving correctly. Really good chance it was built by the lowest bidder some place near China Or perhaps the gauge is lazy or the wiring is not communicatin or something solid state is not
I've replaced my sn52 sender once, but I didn't buy the Classic brand replacement. Bought one for much less on epay. New one works great! Phil
An easy test is with a 250 ohm potentiometer... "register 0 psi at 240 ohms resistance, 50 psi at 105 ohms resistance, and 100 psi at ~33 ohms resistance (the lower the resistance, the higher the psi reading)." All you do is clip lead from center to one end, ground either end. Center clip to gauge. Then go by information above. If gauge is ok, replace sending unit which has to match resistance for accuracy. Sent from my SM-S320VL using Tapatalk
I know I’m not getting resistance, the question is why sometimes and not other times. I keep thinking it’s a grounding problem but tried a direct ground and still have the problem, my only other guess is that the resistance wire gets hot . As I said earlier- frustrating! Sent from my iPhone using H.A.M.B.
It's an extremely simple circuit. The information was from their site...0 psi at 240 ohms resistance, 50 psi at 105 ohms resistance, and 100 psi at ~33 ohms resistance (the lower the resistance, the higher the psi reading). Sending unit has a potentiometer inside so that as pressure increases resistance decreases. With an ohmmeter check resistance from gauge ground to sending unit terminal. Should be about 240 ohms, engine not running. Then start it. Resistance should decrease as pressure increases. There has to be a good ground engine to body and frame and dash grounded. Sent from my SM-S320VL using Tapatalk
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