Oil Pressure

#1
Well folks, re P6 3500 auto 1974
Another stupid post, do P6s have ghosts? I am bloody sure mine has, my old grandad never did like me, and he is haunting my car. As soon as am nearing the project finish, something else goes wrong, (see my previous posts) Started her up last Sat, lovely, until smoke billows from the engine, I hadn't notice but the return fuel pipe had somehow moved and had touch the exhaust pipe, petrol every where, very scary, OK, replaced that, after changing my pants. But of course on restart, still plenty of gas still soaked into the manifold, OK, so I had another go yesterday, started well, crikey no oil pressure, this is why I now have the alternator of AGAIN,
Now, two pressure switches on the oil pump, just visible. Having had 50psi before, I am hoping its not the pump.
I am guessing at the smaller switch is an indicator light which comes on with ignition?
The larger one, goes to the pressure gauge I assume
So before I throw a bomb under the car, all comments, as long as I am not pilloried, (been watching the Musketeers on telly, bloody rubbish) welcomed,
By the way grandad is also moving tools and parts from my garage.
Men in white coats has just knocked on my door, so I will be OK soon, I am 83 this Sat, so make excuses
Make sure you keep away from the bug
Best wishes
Brian
 

quattro

Administrator
Staff member
#2
If the oil pressure light comes on with the ignition, and goes out when you start the car, then you have oil pressure, maybe not much but you do have at least 7 PSI. If it doesn't go out, turn the engine off and don't start it again until you have sorted the problem. If there is no pressure, it would pobably rattle like hell btw.

P6s do not have ghosts, the P666 may have to odd demon or so though, so beware.
 

jp928

Well-Known Member
#5
The small switch is the idiot light, the bigger housing feeds the pressure gauge. New items can be $$$$.
 
#9
Right Then Cock, cockney talk. I think it means "I agree with you mate"
Anyway thanks for all the info, will investigate switch today, it is a bit harder to get at, so I am not looking forward to it
Brian
 
#10
OK folks me, AGAIN. 3500 jinks
I put the alternator back, fired 666 up, besides loads of smoke omitting from the exhaust manifold, still a bit scary, I have no oil pressure, and the pressure light does not go out, so quickly turn off.
So what is the problem? electrics? pump packed up? do pumps of this type have any records of complete failure?
I have never in all the years I have spent under countless cars, other that drive shafts snapping on some, come across this.
So any advice on this?
But seriously folks, I would like to keep with this one, and keep grandad, weird number plates, rhyming slang, army days, etc, on hold.
Will stop crying, hoping to get a solution.
Regards
Brian
 

quattro

Administrator
Staff member
#11
Oh dear, that doesn't sound too good.

You can test the electrical side of it by having someone sitting in the car, with the ignition on. Then pull the wire off the small sender on the oil pump and hold it against the engine (earth it) for a second or so. The warning light should go out. Then put it back and pull the wire off the large sender and hold that against the engine for a second or two. The pressure gauge should then go up.

Did the engine sound very rattly when you started it?
 

harveyp6

Well-Known Member
#12
You can test the electrical side of it by having someone sitting in the car, with the ignition on. Then pull the wire off the small sender on the oil pump and hold it against the engine (earth it) for a second or so. The warning light should go out.
Pulling the wire off will make the light go off, earthing the wire should put it back on again.
 

jp928

Well-Known Member
#14
I have experienced a total oil pressure loss due to pressure relief valve sticking open - MX5. That required a sump drop to access the valve. With the filter off you may be able to undo the plug on the valve - if it is stuck open there will be quite some pressure in the spring, so take care. With the MX5 i was able to grab the hollow piston with a thread tap so I could pull it out - tightly stuck. Cleaned it up with some fine wet'n'dry, refitted, done several 1000kms now, albeit with lower oil pressure than I would like, but no noises. This same problem is also not uncommon the Chev LS serties of engines, also with a crank driven pump like the Mazda. Plan to replace the valve in my rebuild.
With filter off you might need to remove the pump cover to explore the valve, but then you need to fill it with vaseline to get it prime.
 
#15
I have experienced a total oil pressure loss due to pressure relief valve sticking open - MX5. That required a sump drop to access the valve. With the filter off you may be able to undo the plug on the valve - if it is stuck open there will be quite some pressure in the spring, so take care. With the MX5 i was able to grab the hollow piston with a thread tap so I could pull it out - tightly stuck. Cleaned it up with some fine wet'n'dry, refitted, done several 1000kms now, albeit with lower oil pressure than I would like, but no noises. This same problem is also not uncommon the Chev LS serties of engines, also with a crank driven pump like the Mazda. Plan to replace the valve in my rebuild.
With filter off you might need to remove the pump cover to explore the valve, but then you need to fill it with Vaseline to get it prime.
 

quattro

Administrator
Staff member
#17
Personally, and for no other reason than it's what I would do, I would mark up the dizzy to ensure correct re fitment, then lift it out and shine a torch down into the front cover.
 

jp928

Well-Known Member
#18
If it runs and produces zero pressure then the possibilities are limited:-
- oil is escaping in bulk from collapsed bearings suddenly - unlikely.
- the drive gear on the dizzy has broken - pull dizzy and check, but if it runs, not plausible.
- the drive gear on the camshaft has failed - pull dizzy and check, but as above.
- something is blocking supply into the pump , or it lost its prime.
- something is dumping pressure back to the sump, as in the relief valve.....

As above suggestion, mark dizzy and pull it out. Make/get a tool to spin the pump with a drill and see if you get much resistance/load, and any pressure reading. Background - once helped a mate rebuild a SB Chevy. When we were ready to start it, we removed coil HT lead and ran the starter to get oil pressure up - initially it turned quickly and easily, but as soon as oil pressure appeared the starter slowed markedly, easily heard by both of us, so pump under load should be noticeable. IMHO anyway, although I havent heard it on this engine. At least you dont have to pull the sump to get at the pump.
 
#19
Thanks again people,
So, I removed the dizzy very carefully, and marked. What am I looking for? I can see the gears, and also a drive peg, this I turned 180 degrees with a screwdriver, hardly any resistance, turned back to original position. Should there have been oil in sight, because there was not. So??
Another question, I cannot find any reference to the oil pressure gauge switch (the larger switch on the pump) in the wiring diagrams. Where does the wire go to?
I am thinking, the gears on the cam turns the dizzy. The dizzy drives the oil pump?
Regards
Brian
 
Last edited:

harveyp6

Well-Known Member
#20
I am thinking, the gears on the cam turns the dizzy. The dizzy drives the oil pump?
Correct. You won't feel resistance turning the drive with a screwdriver, you need to spin it up with a drill and check for oil pressure either with the light or guage, or with a rocker cover off checking it coming up to there. You shouldn't see oil laying down the distributer hole by the oil pump gear shaft.
 
Top