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2G Replacement Oil Pressure Sending units and pressure readings

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Kryndon

Proven Member
944
591
Jan 10, 2014
Bulgaria, Europe
Backstory:
A year ago I suddenly noticed that the stock oil pressure gauge was reading awful low, settling just above the lowest white mark at idle (~750 RPM). At cruise around 2k RPM it was still under the midway mark. So I thought maybe the original sending unit got weak and was reading lower than usual (both balance shafts are deleted and I'm feeding the 16G from the head, so oil pressure should definitely be higher than stock!). I had a spare used 6 bolt sending unit on the shelf so I put that on, but again it was reading exactly the same as the old one. I hadn't really done anything to the car prior to this sudden change.

Fast forward to recently, I switched to 15W-50 for other reasons but also to see how it would affect the pressure; and it didn't. Gauge was showing always under the middle mark and only ever went slightly above it if I was hammering on the car. Also, the needle itself moved fairly slowly. So a few days ago I ordered a Beck&Arnley replacement sending unit (BAR 201-1799) from Rockauto and installed it yesterday. When I started the car up, the needle went to the very top and stood there for the entirety of the warm-up period. I went on a drive and I noticed sometimes it went back down to the lowest mark during idle but then it really quickly moved up as soon as i started revving and accelerating. Now it seems the needle is hovering above the middle mark around 2000 RPM in city driving conditions. The needle is now much more erratic and responsive to RPM changes.

When I compared the OEM unit to the aftermarket one, I noticed the OEM has a pinhole sized entry for the oil to flow through into the sender, whereas the a/m one is noticeably bigger. I'm starting to think that the a/m unit is either faulty or the little hole diameters have an effect on the readings, because if you think about it, a smaller hole will cause the pressure of the oil entering it to rise, and a bigger hole will have less pressure but more flow. So could this be affecting the way the needle on the dash moves? If so, why would companies make replacement sending units with such a design change? I compared to other units and they also seem to have a much bigger hole. I'm also wondering if the pinhole opening on the OEM unit is acting like a filter to make the gauge needle move slower?

At this point I am unsure whether my original 2 OEM sending units were bad or if the new one is OR if I have some weird oil pressure issue (engine was fully rebuilt in 2019 so I'm less inclined to believe it's a mechanical issue). Also the wiring to the sender and switch are in good shape with fresh/clean connectors.


If someone has used the Beck/Arnley oil pressure unit or any other replacement, can you please share how it affected your pressure gauge needle?
 
I haven't installed a beck/arnley pressure sender before but I can say that of all the cars I have ever had the facory dash oil pressure gauge is nothing near "erratic" they usually do just about what you said yours did with the old pressure units. Altho mine usually went a little above the middle on start up.

I'd recommend installing an aftermarket gauge with a pressure line. That's what I do on all my cars. That way you know what you've got for sure. I may try a beck/arnley sender and see what happens on my cars. It would be nice to have the factory gauge more responsive
 
Well after a few days of driving around with the Beck/Arnley unit, it seems that when it settles, it reads like the old one, so at idle I get real low pressure (which still makes no sense in my case!) and sometimes it will sit at the middle during cruise. HOWEVER, it's still 80% of the time way up like almost topped out so I'm thinking it could be the bigger opening. I'm unsure whether to put back the old OEM one, look for another used OEM unit or stay with this one. Aftermarket gauges are out of the question for now.
 
Oil pressure gauge behavior has bothered me too. I've been driving my 'new' 95 GST (149k miles on an engine of unknown history but very clean) for most of a month and the gauge behavior has been exactly as Kryndon describes in his first two sentences: Always below halfway and at hot idle pretty close to the bottom. And moves relatively slowly.

Looking in the Talon owner's manual (can't afford both a GST and a decent GST owners manual!) on page 71 there's a picture of the gauge with a 'normal range' marked that goes from right about what we're seeing at hot idle to just about the top mark which is as far from the top as the low end is from the bottom. So the manual suggests what we're seeing is normal for these cars.

Where I live we've not seen an AM below about 50 since I got this car and 'cold morning start' is when you'll see the highest readings.

The idiot light on my car works; I have never seen it even flicker when idling so there's that checkpoint. One of these days I'll put a gauge on in place of the sending unit and start the engine just to get a calibration check on the dash gauge but I think what we're seeing is okay. Minimum 'ok' pressure is 18 psi per the shop manual if I remember rightly.

FWIW the sending units for these gauges have to be pretty tough: Mitsubishi says oil filters must be rated for at least 400 psi and when I once left a 200 psi gauge on a 4g64 engine that gauge was destroyed by overpressure within a month. The pressure surge when you start can be pretty extreme in winter.

How quickly the gauge responds is just a design decision. "How fast do you want it to move?" Small orifice = slow because of the viscosity of the oil. Easier to get clogged up, too, but if you've got oil that dirty at that place, there are bigger problems than gauge movement coming real soon.
 
Oil pressure gauge behavior has bothered ...
Good points all around. I have the original '97 Talon FSM and I need to cross-check on that page 71. Again, we all know the needle isn't showing specific psi values but I have noticed it change resting positions in cases when I deleted balance shafts, mistakenly left the front balance shaft oil hole unplugged (don't even ask), rebuilding the engine with fresh bearings and even changing oil weight. I also replaced the oil switch (dummy light unit) for good measure but I've never seen it light up either, so there's definitely enough oil pressure to keep the system happy (plenty of oil squirtin' from the lifters), even with the needle so low. Also, one last thing, the voltage reading might not correspond right once you hook up the sender to an aftermarket gauge so keep that in mind.
 
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