still dont understand oil pressure
 

ok, my oil pressure is really wierd, when i start up my car it will go to 60psi and everything, and it will sit there when its warming up, but when im driving normally its wierd, it will go to almost 60psi when im accelerating but when im just cruising at like 3000 rpms it will be at about 45psi, and when im idleing at 750 it will almost drop to 0 not quite, but its close enough. so i dont know whats up. its really getting me worried, because i dont want to fry my engine it only has 13,000 miles on the rebuild. so please any info anyone has that could diagnos this problem would be very helpful. thanks.

kyle

Thats happened to two of my ReXs... each time I put in a new oil pressure sending unit it quit giving me erroneous readings... sometimes even cleaning the contact point of the wire helps since some oil can get on it when the filter is removed during changes.

NEVER trust an aging gauge. To have a much more accurate or a second opinion, install a mechanical gauge in the rear banjo fitting. Just buy the cheapy at autozone and that will ease troubleshooting headache.

Excellent advice from both of you. That exact problem plagued me also, a new sender fixed it. And do the cheapy mech gauge right now to make sure its just your gauge and not a real problem. Much cheaper insurance than a new motor.

Wow, my '85 GS has done the exact same thing since I got it, and was thinking about getting around to asking this same question. I have a basic idea of how this can work, but I'm fuzzy on a few things so please forgive my idiocy.

1) Where is the oil pressure sending unit located? How much does a new one cost?
2) What do the contact points of the wires look like? Are they visible? If cleaned could they solve the problem?
3) What is a banjo fitting and how does one install a mechanical gauge into one? How do the mechanical gauges work?

Just a few questions I had about the whole thing since I'm still learning as I go. My mechanical ability is limited at times but I've taught myself everything I know so far with the help of you guys here, and I must say I know way way more than before I bought this car. :D

Thanks in advance!

The OP sender is located on the left side of the engine, below the oil filter. Its a gold colored bulb lookin thingie. It has a single blade connector that slides on from the side. Cleaning it may help. To install a mechanical gauge. Most of them come with what you need. Youll need to remove the existing sender, then screw in a 1/8" npt nipple (use teflon tape on the threads to prevent leaks). The assemble the fittings for the gauge per the instructions and connect to the nipple. Yes I like saying nipple. :D

So the gauge just kind of squeezes in between the stock components and then you reassemble everything like it was before?

Also, the gauge is meant to be permanently left in the installation location? So if you need to check you just crawl under the hood and sneek a peek to make sure everythings okay right?

No the gauge will mount inside the car, only the sending unit or in this case the line for the mech. gauge will be under the hood.

Your choice. You can just temp mount it, or run the hose into the cockpit and mount the gauge somewhere. If you want to use both gauges, then youd need a 1/8"npt Tee to T them both in.

I just took the rear banjo bolt for the oil cooler out and tapped the end of that to except my guage. Not installed yet but should work fine. The bolt is really soft metal so it is easy to drill and tap. A cordless drill should do it, even though I used a heavy duty drill press.

well thanks guys, that was all very helpful. it really puts some of my worries to rest, i will check all that and see if it helps

nipple nipple nipple nipples niplets nippin flashin the low temp indicaters nippers lovethumbs joystickies yea yea huh huh yea

Easy on the saturday night booze there Dankus, or don't drink and post ;)

I was having the same problem (the oil pressure not the booze) and was wondering exactly the same. I knew pressure would go down when idleing, but when I was seeing the oil pressure at 40 while going at 6500 rpm in 4th gear, I was starting to worry. So I shall check that sending unit.

BTW before I go trying to fix things, what is the oil pressure supposed to be? Then maybe I'll know if things are working okay or not! lol

3,000 rpm = 64 ~ 79 psi
idling = 12.8 ~ 38.4 psi

So if I never get a reading I should just replace the sender.
(only half of my guages actually work right know)

So the oil pressure IS supposed to fluctuate depending on the RPM of the engine? I thought it was supposed to be constant.... (shows how much I know) :D Maybe I'll have to go take another look at mine, it might be okay after all.

Can someone explain to me conceptually why the oil pressure changes with the RPM of the engine? I figured it was always the same...

in a stock gauge, the oil pressure closes the contactors inside the sender which in return sends an electrical signal to the gauge. Whereas in a mechanical gauge, you have a direct pressure that pushes the contact points in the gauge. anyone else wanna give this a shot? writing is not one of my strenght.