I guess I'm a trusting soul, my gauge has been acting funny for 10 years, it reads fine at idle "35 PSI", then acts normal up to about 1500 RPM where it gets to about 45 PSI then it starts jumping and pegs out. I figure it has oil pressure so I've never screwed with it. SBC's seldom have oil pressure issues anyway.

If you have fuel injection the oil pressure sending unit that is near the oil filter probably is just an on off switch. It's purpose is to tell the computer that the engine has a minimum level of oil pressure so it keeps the fuel pump running. If that sensor goes bad it will either say you have oil pressure when you don't, and let the car keep trying to run, or it will say you don't have oil pressure when you do and that will shut you down and not let the car run.

The switch type sensors are usually smaller than the bell shaped sensors that are used to drive gauges. The switch type sensors are either on or off depending on their being a minimum oil pressure.

The bell shaped sensors are more or less a variable resistor whose resistance varies depending on the oil pressure.

They also made combination sensors that had both types of sensors in one unit. These combination sensors will have at least 2 connectors and more than likely three connectors.

To summerize,

If you are just feeding an oil pressure gauge you need one wire going from a bell shaped oil pressure sensor/sending unit.

If you are running fuel injection you need at least an on/off oil pressure switch that works correctly. If you also have an oil pressure gauge you then need above mentioned bell shaped oil pressure sensor/sending unit. With the caveat that the two types of sending units could be combined into one on some years of 3rd-gens.

There are at least two different places the sending units could be, either near the distributor, just to the drivers side of it, coming out of the top of the engine, or down by the base of the oil filter assembly. Both places have access to oil pressure and both may be used for either unit.

dzimmerm

Replaced my pressed leaking piece of crap 92 style oil pressure switch with the #3 one a couple days ago. Idiot who installed the previous one didn't even use any teflon tape on the threads. The replacements are much easier to tighten and loosen. Now my guage actualy shows the pressure, rather than just pegged passed 60 all the time.

Safemode

I tried using the regular white teflon tape when I installed my oil pressure sender unit, bell type, up near the distributor. That teflon tape did not hold up well with oil and heat, and I removed it and just snugged down the fittings, which were brass.

Is there another kind of teflon tape made specifically for hot automotive oil applications?

As an aside, I recently did use white teflon tape to seal a fuel pressure tester joint, between the pressure meter and the adapter line that fitted to a test port on the fuel rail. It seems to work fine for a limited testing time I used it. So it might be the heat that bothers white teflon tape rather than the oil/gas.

dzimmerm

teflon can handle up to 500 degrees .... perhaps it's the gasoline....perhaps something else. I dont know. Mine is located down by the oil filter, I'm gonna check how that seal is holding up in a couple days ....or maybe today.

Just get thick PTFE plumbing tape. Not the real thin stuff.

Did some testing on my oil sending issue, I have the electric fuel pump so I did the test on the bell shaped oil sending unit beside the distributor:

1. with the cable disconnected, the odd position pin read 0 ohms.
*__* Plug

2. With the plug odd pin grounded and the key in run, the meter went to 0 on gauge--to the left!

3. With the motor running the odd pin on sensor, read about 14.25 ohms.

4. With everything connected and the motor running, the gauge read near the highest point.

** the asterisks denote the odd pin on sensor/plug. The other two pins are perpendicular to odd pin.

Ideas?

PTFE ...aka teflon is good for 500 degrees plus, however it will not hold up to petroleum based products, your best bet is to use a rtv sealant, which is capable of withstanding high heat as well as petroleum based products,

Your car is a 305 TBI car, your sending unit is going to be above the oil filter. The hardest part is using some channellocks to get it off and screw the new one on because you have to grab on a part of hte unit that's behind the oil filter flange. Annoying and tedious, but not impossible.



On my 1992 RS, just after replacing it. It's a $15 part...

Did a search and this was the best/longest thread on the oil pressure sending unit despite lots of conflicting posts within it.

My question...
For a stock sensor on a 1991 305 (3 wire, above oil filter) what tool do I need to get it off? I have found one person that said 30mm deep socket and another that said 1-3/16" deep socket which are both essentially the same size. Is this correct? (I'd have to buy it) I tried open/boxed wrenches and adjustable wrenches on the hex part and vise grips on the cylinderical portion and nothing works or fits with enough swing room. Oh, and I am also expecting nearly no oil to come out, correct?

I used a gm oil pressure switch socket from pep boys that could use a 3/8 ratchet or a 7/8 wrench. the switch is longer than the socket though so I drilled out the end for the ratchet untill the sensor would fit through and then just used a wrench on it.

I chuckled at this... had to replace mine and I spent so long on this, then felt incredibly stupid when I realized it was the wrong hole!

Just replaced mine on a 1991 Camaro. Had to use a vise-grip on the old one to get it off. I purchased a 1-3/16" oil pressure sender socket at the parts store but you can't get it on because the frame rail is too close. THe replacement sender is much smaller and the socket I purchased for that (1-1/16") fit and put it on in a charm.

The photo above from InfernalVortex looks like my aftermarket replacement. BTW

Hey you guys seem pretty knowledgeable about this. Maybe you can help me? I just changed intakes and don't have clearance for my old school sender, so I'd like to move it near the filter. I have a goodwrench replacement in there and just removed the oil plug, but the thread is 1/4 NPT is that right? With the above pic I confirmed its in the right location.

Here's a good pic to illustrate it:



You can see a plug just above the oil filter. Is that the correct hole? Mines 1/4 NPT.

Yeah the hole with the bolt in it is the one you need to put the sending unit in.

Can you confirm that the thread 1/4 NPT? Its got me worried that all the senders and safety switches are 1/8 NPT.

guys, how the HELL did you get the old one off? I read over this, got the sockets which don't go over (but got them anyway for the new one) due to no room, tried a 1 inch open end wrench and the oil filter mounting flange is in the way, and the same with this vice grip! i can't get it at an angle either.

Forget about grabbing the nut part of the sender. I had to vice grip the sensor and partly smash it to get it off. The new one went in easy with the special socket. (its smaller)

oh man, i started turning it with my HAND and actually thought i was turning it but only turned the body, and not what screws in.

This is exactly how I had to get mine off too.

DAMNIT! guys I need serious help. like I said, I couldn't get it off anyway even with vices. so I thought of cutting the sensor off so I can get to the nut but some oil has come out! is this normal? I thought no oil would come out when you took the sensor out? the car is now pretty cold.

There may be a little oil behind it but as the engine is not running it's not pressurized and most of it will be drained back into the oil pan.

I used some channellocks to get to mine. It's a bit annoying and tedious, but not impossible. Just angle the channellocks to get to the nut on the sending unit and turn it as far as you can while grabbing as hard as you can. It'll come out eventually.

May be doing this tomorrow on my 90 RS with the 305 TBI, as my gauge reads zero all the time, and before that it used to peg under hard acceleration.

So just smash the old unit with the vice grips and tear it out since I won't be able to get to the nut anyway, and then buy a 1 1/16" socket (a special kind or just a regular?) to stick the new one in with ease?

Also use Teflon tape instead of thread locker and just wrap a piece around the threads on the new unit before installing it?

the new part comes with sealant on the threads already.
and yea I think I used a regular socket that went around the sensor. the special socket would not fit because of the frame rail.

Very Helpful picture... takes all guesswork out of "where is this thing?"

Took me ten minutes. Channel locks to take the old one out. an adjustable wrench to put the new one in. $27 and its a bit shorter overall but the place to put the wrench was farther out making it easier to put in. Only issue I was annoyed with was my headers nb o2 and wb 02 sensor locations - right in the way...

I have a 90 iroc just needed to get the exact location of the oil pressure sending unit for my car, any info?

got it everyone thanks!