The verdict is in!
Condition...Low oil pressure showing on your dash guage...Idiot light blinking at idle.

I encountered this condition recently after changing a bad sending unit to a new Neihoff sending unit.

Doubting very seriously that I had a bad engine, 120k? miles on a VERY well maintained engine I decided it was time for an experiment. I went out to the local parts store and picked up the following...

2 GP Sorenson Oil Sending Units
2 Neihoff Oil Sending Units (forgive me if I spelled it wrong)
1 High Volume Oil Pump (just in case)
1 Mechanical Oil Pressure Guage

After getting home, with a nice warm engine and an already blinking idiot light on my guage panel I pulled the Neihoff sending unit that I put in last weekend and replaced it with a GP Sorenson unit that I just bought...amazingly my pressure was now reading about 35 PSI. This by the way was pretty much what the old unit read before it went out and was replaced last weekend. Thinking maybe I had bought a bad Neihoff unit last weekend right off the shelf I pulled the GP Sorenson out and put a brand new Neihoff in....hmmm....back to the blinking idiot light. By the way, if I had to guess, using the guage pod oil pressure guage, I would say the pressure reading for the Neihoff guages were about 5 PSI or less (just a guess but it was at the very low end of the red).

With this I decided it was time to use the mechanical guage and find out for sure. The reading on the mechanical guage...at temperatures ranging from 180 to 220 was a solid 25 PSI. I want to add a disclaimer here as well...I only hand tightened the mechanical guage and did notice I was leaking oil from it after the test...so could my pressure actually have been higher?...more than likely, but for the sake of my test I was satisfied with my results. So, I then tried the remaining two brand new units (1 GP Sorenson and 1 Neihoff) Both had the same results as above. I ended up putting in the GP Sorenson and taking the rest back to the store and getting my money refunded.

Lesson learned...

Get a mechanical guage and find out what the pressure really is in your engine and get a sending unit that best reflects that pressure. In my case it was the GP Sorenson. That one was the least off in PSI (it only read about 10 higher) Needless to say I am keeping the 20w50 in my car for now with an additive to increase viscosity...just for peace of mind.

Regardless of the condition of your engine you should be able to rely on the accuracy of your instrumentation...get it as close to actual readings as possible. I hope this helps some of you out there with this same problem.

------------------

same for me almost. my sending unit went out (actually the fuel pressure switch part. was keeping my fuel pump on). when i changed it my oil press. guage read too low.

mine i guess actually is too low though. about the same time i see the see through engine bay thing, and had some spare guages i put in to show what the engine was doing, like repeaters (put a tee in for two independent senders). while i was doing this i broke the new unit and had to buy another. now with the new unit and the repeater both read too low. the car runs the same though, so i drive it and hope i don't get a nasty surprise when i least expect it.

------------------
Phil T.

start where you are,
use what you have,
do what you can. arthur ashe

A good post. Neihoff makes sending units for many vehicles and perhaps they have some mis-packaged units, or have opted to use a '1 unit fits many' attitude, with accuracy just a ballpark idea. Would you mind posting the Neihoff part #s please?

Your results are exactly why many of us here keep telling people to test with a good mechanical gauge any time there is an oil pressure issue. You can never trust the dash gauge even when the sensor is perfect. There are a bunch of things that will screw with dash gauges for oil and temperature.

I would guess that the Niehoff senders are the wrong ones. Wrong part in package and wrong numbers in parts catalogs are fairly common. Look at the problems Stant catalog keeps causing... Mechanically all oil pressure senders are pretty much the same. The main difs are pressure range and resistance range. The 80PSI sender can have different resistors in it much like there are variations of fuel sender resistance between car brands.

Some people are tempted to leave a mechanical gauge on an engine full time. Unless you have one made for that, don't do it. The vibration can cause the tube in the gauge to break, usually resulting in the engine quickly draining all its oil.

25 PSI is still low. Spec is 35-40 at all times. (Yes all times) Your engine isn't bad but it likely does need some work. The V6 used in Fiero and other GM cars is especially well known for getting sloppy in the crank bearings. Assuming the gauge is accurate, a small drip at the gauge would not account for a low pressure reading.

------------------
The only thing George Orwell got wrong was the year...

The Ogre's Fiero Cave (It's also at the top of every forum page...)

Niehoff are junk,I had the same problem,my old leaking sender would read 35-45 lbs at all times put in a Niehoff and I dropped to near zero at idle and top out at 35 at 4000 rpm,I've heard the same about other Niehoff products such as wires caps etc.

I don't have the part numbers handy right now but I'll get them and post them as soon as I can.

You can check an oil pressure sender pretty easily before you install it in your car.

Just temporarily connect the new sender to a regulated source of compressed air and measure the resistance with an ohmmeter. (I just hand tighten a 1/4-18 npt shop air quick-connect fitting onto the sender.) According to GM, the resistance should be near 0 ohms at 0 psi and 90 ohms at 80 psi. Testing by Oliver Scholz and others has confirmed this to be correct. My own testing indicates that the change in resistance of a new Delco sender is pretty linear above 20 psi but somewhat non-linear below that. Don't be surprised if a brand new sender is a little "notchy" (i.e. the resistance doesn't change smoothly with changes in pressure); I think that's probably normal until a new sender has been in service for a while and has gone through at least a few dozen cycles.

Allowing for measurement errors, a brand new sender should be within +/- 10% of the correct value (i.e. measure between 81 and 99 ohms at 80 psi). If not, take it back.

[This message has been edited by Marvin McInnis (edited 03-20-2005).]

The resistor is a wire wound item and may never change perfectly smooth. This sensor and gauge is ment only as a rough estimate of oil pressure. The actual pressure is nearly always +/- several PSI. The only accurate measure is a high precision electonic or a good mechanical gauge. The oil pressure gauge in most GM and other cars works about the same as the fuel level gauge. They are anything but totally accurate.

quote Originally posted by theogre: The resistor is a wire wound item and may never change perfectly smooth.

Agreed. The "notchiness" I was referring to normally lasts only until the wire and/or slider in a new sender are burnished smooth by normal operation.

quote Originally posted by theogre: The actual pressure is nearly always +/- several PSI. ... The oil pressure gauge in most GM and other cars ... are anything but totally accurate.

Again, I agree. However, in preparing for my first post in this thread (and to keep myself honest) I tested a brand new, fresh-out-of-the-box Delco oil pressure sender I bought recently for my 1991 Buick 3.8. The factory manual specifies (in several places) 86 ohms at 80 psi ... pretty typical for GM ... but it actually measures 60 ohms (repeatably) at 80 psi, which is 30% low. That is outside of my personal acceptable range of error.

I did verify that the part number stamped on the sender is the number currently listed by Delco on their web site and in their catalog. The question remains: is the Delco listing wrong or is the part itself defective?

Thanks to powrmajik for bringing this subject up. I really hate replacing things twice!

[This message has been edited by Marvin McInnis (edited 03-20-2005).]

I got a BorgWarner sender that behaved just like those Niehoff ones. Put the jumpy old one back in. Anybody else use the BW?

I've had a T in my oil pressure line for the past 8 years... one mechanical gauge in the engine compartment and the stock sending unit for the factory instrument cluster guage. Knowing the inaccuracy of factory GM gauges I thought this would be cheap insurance just incase of sending unit failure.

There are mechanical gages that can withstand the vibration, but they aren't as cheap to purchase. I have a 4" liquid filled 0-100psi gage off an oil well drilling rig I use for oil pressure testing and wouldn't be afraid to leave it connected full time, except it weighs about 2 lbs. Might break the nipple or tee off over time. Back when I 'liberated' it, they were about $100.

quote Originally posted by Dino: I got a BorgWarner sender that behaved just like those Niehoff ones. Put the jumpy old one back in. Anybody else use the BW?

Niehoff is a division of BWD Automotive aka Borg Warner. They are the same company.

edit:

More info.

Borg Warner, Niehoff and a bunch of other aftermarket brands were (are?) part of Echlin. Echlin merged with Dana in 1998 and now all the companies are in the Dana "Automotive Aftermarket Under Hood Group".

The group consists of Wix Global Filtration, the Engine Management Division (BWD Automotive selling the Niehoff, NAPA Echlin and Borg Warner Brands, Beck/Arnley Worldparts), the Clevite Engine Parts Division, and Dana World Trade.

Guess they keep the old brand names to make us think we have a choice. But all the brands are likely now made in the same Chinese plant.

[This message has been edited by spark1 (edited 03-21-2005).]

Well this is an interresting thread! Most of you were a great help.But Spark1 through me way off compared to the rest of the comments. BTW I do have a mechanical gauge in the engine compatment.It reads around 20/25 psi at idial.SOOOO! does anybody have any idear what is a good sending unit? I DON"T like to see the gauge fluttering all over the place. At idial, the red light comes on but if the gauge is steady at driving range it reads 35/40 psi.

[This message has been edited by 87V6GT (edited 05-31-2005).]

quote Originally posted by 87V6GT: BTW I do have a mechanical gauge in the engine compatment.It reads around 20/25 psi at idial.SOOOO! does anybody have any idear what is a good sending unit?

In a nutshell - they're all crap!

I swapped out 4 in a row for one guy until we nailed one that wasn't either pegged over, flickering, fluttering (or just doing whatever!).

I've used Niehoff, Delco, and a few others I can't remember. They've been early style, late style (for some reason these croak more??).

Use the dash gauge as a reference point - and the mechanical underhood one for 'real' readings.

Thanks. I think i'm going to put some stop pins at each end of the gauge so the needle does not travel so far. When I do that I'll put some on the temp.gauge allsoThat.will help keep the temp.needle from pegging and geting stuck.Thanks again.

I replaced the oil pump and pickup on the vette after a new aftermarket sender still indicated very eratic oil pressure after I replaced the OEM sender. It still showed fluctuations from 40-65 pnds just cruising on the freeway. I put a new AC unit in and now it shows a constant 55 pnds at all times like it should. It did need the pump anyway though, it was defective and the pickup tube was worn and about to drop off.

SO! What has the AC unit got to do with the oil pressure??

quote Originally posted by 87V6GT: SO! What has the AC unit got to do with the oil pressure??

He is meaning a Factory AC Delco Part! not Air Conditioning!

------------------

****************************************
http://home.cfl.rr.com/fierose
Central Florida Fieros
http://www.centralfloridafieros.org

quote Originally posted by 87V6GT: I think i'm going to put some stop pins at each end of the gauge so the needle does not travel so far. When I do that I'll put some on the temp.gauge allsoThat.will help keep the temp.needle from pegging and geting stuck.

Why not just do the simple rewiring fix, and it'll never peg again? Way easier to do it that way than chopping up your dash!

http://24.207.69.124/The%20Pegging%20Temperature%20Gauge%20Fix.htm

As I have said in several post that these oil sender units are junk, But I have found that the 88 sender unit works real good. I have a 88 model Borg Warner in my 86 and it reads very close to my mechanical guage. Try the 88 sender and I think you will see a difference. ( all you need to do is change the connector )
Don

For what its worth , I never trusted these gauges either, what I do to check the oil pressure--as I have a dipper too, is hold the pedal or get the rpms to 2000, if your reading 35-40psi on oil gauge, your ok to go.