I've read various posts on how to bypass the idiot light style oil pressure switch (because it's not a sending unit) and just have one question. On the older style sending unit (I believe it's an '87 and older if i'm not mistaken), does it corespond with the scale on the instrument cluster correctly? Meaning when you bypass the resistor on the instrument cluster with a jumper wire, and install the older style sending unit, does it read correctly on the dash? Like the needle in the low part of the normal range at idle and increasing with throttle. No oil pressure would correspond with whatever the gauge read with the key on and the engine not running correct? I'm having the phantom bouncing needle problem (when the engine is warm and idling)and it's been doing it for a while. That makes me believe that I have good oil pressure and it's just a faulty switch. I know that I should put a physical gauge on it to verify this also though. I was thinking about just getting a new switch but would much rather have a physical reading on the dash instead of an idiot gauge. That's why i'm leaning toward the conversion. Has anyone done this, and if so what range does your needle run on the dash? Thanks!

 

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I have an external added so I can see the real pressure on the pillar. (1992) I had an oil pump problem and lost oil pressure long before I realized it. That'll never happen again. I can't comment on what you're asking, but if it reads no oil pressure when its running then the scale is off. Mine sits about 20 lbs at idle. I think, I'll double check that on my way to work today.

 

Thanks for the reply and I could add an external aftermarket gauge but I didn't want to clutter up the dash anymore. If the spot is there in the instrument cluster, I would rather use it if and if I can make it more accurate that's a plus. Also I would be more apt to look at the dash than another gauge too. It has oil pressure (or it would of been dead by now) but when it's warm and the oil is warm and thinned out, it bounces from nothing to half scale. It's because it's reading the open-closed position of the switch instead of a resistance measurement. I think that the switch might be going bad but instead of replacing it or adding the external gauge, I wanted to make it read a physical resistance.

I'm just wondering, of the people that have done this conversion, what range does your stock needle normally run? Also, am I correct on the '87 sending unit? Thanks!

 

Just put a mecanical guage on the "a" pillar. My 94 always read halfway up on the scale, and fall every once an a wile at a stop light. I put a mecanical guage in it, and found that at normal operating temp, at a stop light it had around 10 psi of oil pressure. Ounch! It was only runnin 25-30 psi at hwy speed. Well, I replaced the main, and rod bearings, and the oil pump with a high volume/pressure one, and now it has 40-45 when warm at a stop light, and 55-60 runnin down the hwy. Thatss with 10w30 oil. And this whole time, the stock guage reads the same.. So I would say, if yours is "jumping" around, you more than likely have a oil pressure issue.

 

My truck is a '95 and the current oil pressure unit that is in the truck is an on/off switch. It is only open or closed and will only tell you if you have or don't have oil pressure. Once the pressure gets about 7psi (I believe) it closes the switch and sends ground to the instrument cluster. There is a resistor soldered to the rear of the instrument cluster that only lets the needle go up half way. Your only range in the trucks that have these style units is either none or half way in the normal range. You don't get an accurate reading at all. It's a glorified idiot light and a bad design IMHO. These switches also get old and wear out and give you incorrect information.

What I would like to do is bypass the resistor in the cluster with a jumper wire, install an older style sending unit (that changes resistance with oil pressure), and make the needle move according to the physical oil pressure. This can and has been done by a few people but i'm not sure how much of a sweep the gauge on the dash will give me and what is normal. I might have to just hook it up and put physical air pressure to it and see the range. I just thought that someone that has done it would chime in and see if it's worth while. The resistance range can also be changed by adding a resistor in series to make the needle say whatever you would like it to read. I didn't want to put a mechancial gauge on the A pillar if I had a perfectly good spot in the instrument cluster (where i'm more prone to looking anyways). Thank you for your input and I will put another gauge in it if it's my last resort. I'm just trying to explore this option first.

 

It would be in your best interest to see what the actual oil pressure is on the motor. Even if you just hook a guage up just for a short time. like you said, you can make the guage read whatever you want, and I you never know what your actual pressure is, how are you going to make the guage accurate? I dont know how may miles are on your motor But my 302 only has 137,000 on it, and I had low oil pressure.. That said, my last car had 140,000 on it and had good oil pressure... Find out what your actual pressure is, before you worry about how/ where your guage reads. I'm all for gettin a functional sweeping factory guage, but. if you don't know the actual pressure you can never get the electric one set right..

 

I do plan on checking the physical pressure as the truck has over 330,000 on the clock. I don't think that the motor is original because it still runs really strong, I could be wrong though. I've only had the truck for about 8 months. I did want to get everything that I need though and while i'm in there, do the conversion. I'm just wondering where the gauge will read after the conversion. I'm thinking that i'm going to have to just use air pressure and take some notes of where it is going to read for a specified pressure. Maybe even make some marks on the background of the cluster. Thanks for your help!