I have a 78 vette .... the oil pressure gauge dropped from 40 lbs to 20 lbs. I checked the pressure with a gauge and it was 40 lbs. I replaced the sending unit and it was still 40. I replaced the gauge and nowthe new gauge shows 80 lbs. There is a resistor device on the back of the gauge and a new one came with the new unit. Is there a polarity on this resistor?

 

Welcome to the forum georgiaboy, the gage is not normally the culprit, it's usually the sending unit. Make sure you bought the correct sending unit to mach the gage. If in fact the "resistor device" is a resistor then it wont be polarity sensitive. Check the original gage first, sending unit wire disconnected from sending unit should give you zero PSI, sending unit wire to a good ground should give you full 80 PSI or peg the gage. If you get those readings from the original gage then get a different sending unit. Good luck, get back to us. P.S., I also have a '78.

 

(***I'm only referring to safety as far as oil presure is concerned, and I know that this isn't what you're looking for, however I think that it's a good idea.) In the past, in vehicles that came stock w/ electric-type gauges, I've hooked up mechanical gauges also, oil pressure and water temperature,and mounted them under the hood so that only the original gauges were visible. Atleast this way, if a problem occured w/ a gauge or the engine functions, you could distinguish between the two and take the appropriate actions.

 

Anyone know what year they switched from mechanical to electric? Mine is mech.

 

My 74 is electric, PG.

 

I guess that settles it. The good news about mech. gauge is that it's usually pretty accurate. The bad news is that GM used a plastic tube from the block to the gauge. It's not a question of if it will leak, it's when it will leak. Of course the seepage would drip down on the radio which prevented it from rusting. [sm=happybounce.gif]

Replaced mine with copper line like they used to have. Not sure when they switched to plastic.

 

shark,
I'm for the mechanical gauges, water temp, oil pressure, and the volts hooked into the loop which gives the "net output" from the end, after deducting the drain from whatever accessories are in operation. This way, you can see what accessory has what bearing on your charging system. Then you not onlyhave an accurategauge that keeps you up on thecondition ofeach accessory, but even a trouble-shooting device that can tell you what accessory, if any, is in need of repair.
As far as the plastic tubes go, I've never had any problems w/ them. But you do have to keep the plastic tube away from the exhaust manifold. The problem I have w/ copper is that if it rubs (can get a rubbed spot from vibration) on metal or something hard, it will develop a hole over time, as it's a very soft material anyway. I suppose w/ the proper mounting, both are OK with me. "My opinion ofcourse."

A funny story to suppost your opinion on the plastic line: In '86,when I first got my '62 Ford pick up on the road, I had hooked up a temporary juke box for some sounds. The hot wire for the box was drapped over the plastic oil line for the gauge. I had stopped at a store for a 6 pack which the lady there put in apaper bag.At that time, I was still, on occasion, smoking some weed,and that day was a serious "blow-out." As I was driving along on a quite crowded and busy blvd., somehow the hot wire shorted out and started burning from the shorted out spot across from the passenger side to the driver side just under the dash. The insulation on the wire was smoking like heck and then the insulation coming off the wire caught the paper bag on fire,and also as the wire burnt across the plastic oil gauge tube which itwas drapped over, it melted the oil line and along w/ the smoke rolling out the windows like heck ( it was a warm sunny day) from the wire insulation and now the paper bag, I had a fire on the floor with the paper bag and about 40 to 50 psi of oil pumping onto the floorof the cab. With my girl and I being stoned out to the max, we were laughing so hard that I could hardly keep the truck on the street. LOL We finally pulled over as I couldn't see a thing with all the smoke, and I put the fire out with my feet and pulled the juke box wire from the fuse box. With the metal floor in the old truck, the oil was no big thing. The smoke quickly cleared out of the cab, I took my shirt off to sop up the oil, we popped a beer and took off again tward the house still not being able to stop laughing w/ our stomach muscles and jaws hurting from laughing so much and so hard.
So, in some cases, those plastic lines are alttle dangerous. LOL Especially is you're alittle crazy. LOL

Sorry shark, I have to edit because I left something out, something that gives a positive note to your disliked plastic oil line. LOL I crimped off the oil line coming from the block at the floor board by just folding the line which actually crimps it and then taking a piece of electrical tape from one of my splices on the temporary speaker wires and wrapping it ,which kept it folded. Positive note is that the plastic line, during an emergency, is easy to close off/dead end if need be. LOL Safety First!!! LOL By the way, the juke box really sounded good, and not just because of the "high performance weed stick" that I had operated that day. LOL. I checked the oil later that day. No worry, as those old 6 cylinders held pressure w/ only a quart or two w/ no problem. Been there before too. LOL.

 

Texas: That story could be made into a movie. We could call it "Up in Smoke" Oh yeah, that's already been done. It did sound like Cheech and Chong tho, even the "evil weed" If you haven't seen it, highly recommend it.

Yeah I'm all for mechanical gauges where possible. Especially since the time the Pontiac mech. told me when I was complaining about the oil pressure gauge accuracy (electric of course) in my '68 GTO and he told me that they didn't call them pressure gauges. They called them pressure indicators. Better than an idiot lite I guess.

 

shark,
When I first had that truck, I was single, had a CB1100F Hondaw/ a worked motor, and had an apartment w/ a friend of mine also from NYCwho wasquite abit crazier than I, which at that time was pretty darn crazy. LOL I had alot of very crazy times in that truck and drove it when I was terribly trashed many times also-something I would never do now. Out of all the years I drove that truck, I never got stopped by the police, as out here, the cops don't mess with all original old-type pick-ups, especially if you have short hair, which I had, a crew-cut, at the time. One night I went through a series of cones that the Military Police had set up to check for drunk drivers on Fort Hood after a big concert and festival was over and letting out. I went through and around these cones perfectly and it felt like the truck took itself through automatically. I was in wiped-out condition to say the least after partying all day. My girl and I laughed all the way home after we cleared the cones and the MPs waved us on. I would have been put "under the jail" that night. LOL
Yes, the mechanical gauges are the way to go, I feel,for safety reasons. Although the electric gauges ARE alittle cleaner. Sounds like that Pontiac mechanic expressed it clearly andcorrectly. Pretty clear that he had gone down that road before. I remember in the early to mid'70s, the good tachs in the better drag cars were cable-driven. Ofcourse the cable ran from the tach case which was usually mounted on the dash right infront of the driver. The cable was very evident and ran through the top of the dash. And ofcourse it was cool looking as the cars w/ the cable-drive tachs were the ones that ran. But the set-up wasn't nearly as CLEAN as an electric gauge would have been. Evenwith all the technology of today, I would want a mechanical gauge (maybe hidden) just for safety purposes.