Re: oil pressure shows zero
Zero oil pressure has nothing to do with the fact that the dip stick shows there is oil in the engine. Obviously if there is no oil there can be no "pressure". But just because the engine has oil in it does not mean there MUST be oil pressure. Oil is forced throughout the engine under pressure. If the pump is bad or the bearings worn oil pressure will lower than normal or it may go to zero just before the engine goes to engine heaven.
The gauge needs +12 volts and ground with the key in the RUN position so check that first. Then momentarily jump the "S" (send) terminal on the gauge to ground. The gauge should peg to the right. If it doesn't the gauge is bad (provided you actually checked for +12 volts and ground). If the gauge is ok, then go to the sender. Disconnect the wire and measure the resistance to ground. You should see about 240 ohms with the engine off and somewhere around closer to 40 ohms with the engine running. If that checks ok then the wire between the sender and gauge is open. Check it end to end with an ohm meter. If all of these test ok you did something wrong.
Another way to verify if it is an actual engine problem or a gauge problem is to buy a mechanical gauge at any auto parts store. Remove the electrical sender, install the mechanical gauge and start the engine. If you now have oil pressure you know it's a gauge, sender, or wiring problem. If you don't have oil pressure, then an engine tear down is necessary.
