Re: 1987 Mercury 175HP Oil Alarm
Over the last two years I have been plagued with oil alarms (1987 V6) for various reasons including bad oil pump gear, defective oil warning module and bad outer switchbox. I think the system is basically good , there are loads of motors out there that have run for years with no problems.<br />I would keep the system and proceed as follows !<br /><br />The oil pump motion sensor is a 3 wire device and outputs a square wave signal to the alarm module I think it's 5 volts and it can be viewed with an oscilloscope if you know someone that has one ! This signal must match the supply to No 4 coil, (from outer switchbox)or the alarm sounds. It's rare for the sensor to fail. The plastic gear on the crank might have failed, or partially failed and the pump might be turning a bit now and then , but not always at engine speed and hence the alarm. You must first establish if the oil pump is turning .You can tell if this gear is bad by removing the oil pump (2 small bolts) to reveal the oil pump drive shaft which has a slot in the end. Insert a screwdriver into this slot and turn over the engine slowly by hand (remove plugs) and see if the pump shaft turns okay throughout a couple of engine revolutions. Apply gently pressure with the screwdriver to oppose the shaft rotation and you will know if the plastic gear is okay or not. Don't spin the engine over on the starter or the oil pump shaft will shoot out and might just damage a good plastic gear in the process !<br /><br />If the gear is okay then it might be the float switch in the header tank in front of the flywheel. This is normally open when the tank is full and contacts are closed when oil low. It simply earths out the (blue ?) wire from the oil control module on the port side of motor when the oil is low. Therefore if you unplug the blue wire from module the alarm will stop if it's a float switch problem. You could also do a continuity check across the contacts with a basic meter.<br /><br />A loss of signal from outer switchbox on starboard side of motor to no 4 coil will also cause an oil alarm, often due to a bad swicthbox or just corroded crimp terminals at the switchbox,so ensure these connections are good. Check you have a spark on number 4 cyl when you have the alarm condition. Also check wire from oil control module to swicthbox (No4 coil output terminal). You might not have noticed loss of just one cyl on these motors.<br /><br />Sometimes the oil control module on port side of motor goes bad , on mine you could give it a sharp tap and the alarm would come and go.Check all wires , connections and earths from this module.<br /><br />I understand that the plastic oil pump gear can in fact be replaced without removing the crank, I was billed 8 hours work for mine to be done last year, I know that the crank was left in. The total cost including crank seals which were replaced as a precaution whilst everything was stripped was under £300 (pounds sterling).This was done by a main agent in the UK.<br /><br />Finally don't think the oil pump is working because you see blue smoke. There's enough crankcase pressure in that oil reservoir to force some oil past the pump, which gives sufficent oil and loads of smoke at tickover but not enough as the revs rise ! Hope this helps , good luck !
