Two different Autometer (brand new) oil pressue gauges read the same incorrect oil pressure. Both Autometers read 25psi cold idle & increase w/rpm. Two different mechanical gauges confirm that cold idle is 37-40psi & increases w/rpm.

WTF? Have checked the resistance of the Autometer sender & it is within range. Autometer wants me to send the gauge to them for evaluation. I want to find an electronic gauge that reads correctly. Returnability is not the issue because, as always, Summit will take the gauge back without question.

I'm stuck & dissapointed. Had originally thought that my new Melling was installed incorrectly before finding the gauge issues. Can anyone recommend a reasonably priced ($40-$50) electronic oil pressure gauge that is accurate?

 

Hmm, have you double-checked your ground/wiring to the gauge ? Not to question your mechanical skills, just would be the first thing I would double-check... Odds of two different gauges being off is pretty slim, but hell I just bought two doorknobs the other day from Home Depot that wouldn't lock so anything is possible.

I don't have an oil pressure gauge but my boost/trans temp gauges are the AutoMeter Cobalts (which fall outside your listed price range).

Rob (Bad30th)

 

Thanks for the input. Yes, I quadrouple checked everything; ground resistance, sender resistance, sender wire resistance both connected & disconnected, power on & power off. Also confirmed proper sender resistance w/ Autometer.

With power on, neither Autometer gauge would reach the zero line. So, it would make sense that there's too much resistance somewhere. Autometer says that my numbers are within their expected range. Therefore, it must be gauge calibration.

Here are the numbers. Maybe they'll indicate something that we haven't seen. Sender (engine off) grounded w/ no sender wire connected = 252 ohms, Sender grounded w/ (engine @ idle) & no sender wire connected = 62 ohms. Again, Autometer reads 25 psi when mechancal gauge reads around 40 psi.

I think I'm gonna go through the hassle of running an oil pilot line for a mechanical oil pressure gauge.


Edit 11/9:

Wanted to post the outcome. Both Autometer gauges were & are incorrect.
Just be aware of this possibility after a new oil pump/gauge install. Check the correctness of the gauge before thinking that your new oil pump has a problem.

Installed a VDO replacement (gauge & sender) today using the same gauge ground, sender wire, gauge power & ground source as was used on the Autometer gauge. Took some pics to send to Autometer. The needle on the VDO gauge moves from its' un-powered location exactly to its' zero line when powered & it reads very close to the same pressure as the mechanical test gauge. The Autometer gauge needle moves from its' unpowered location to a position well below the zero line & reads an average of 13 psi less than the mechanical test gauge. I think that it's because the Autometer needle starts from a position well below the zero line, but, it could also have a scaling issue.

The pics show the unpowered & powered starting position.

 

TTT for edit

 

Wow, good find ! Congrats on getting it figured out.

Rob (Bad30th)

 

Have the same problem with an autometer ATM4427 oil pressure gauge. 10 - 15 psi out compared to 2 snap on test gauges. Fired up a 6 grand engine with only 30- 35 psi cold oil pressure. After a sleep less night, considering pull the engine triple check pump/bearings/o ring ECT, done the obvious and checked gauge .Disappointed in autometer to say the least. It’s now a garden ornament with a bullet hole in it.

 

Beleive it or not, Autometer's response to me was that I'm an idiot & it's not possible for their gauges to be off. I'm sending the emails, the gauge, & my photos to Summit when I return the Autometer gauge for the second time. Maybe a large distributor like Summit can get Autometer's attention.