NO Oil pressure - Zilch. Possiable Reasons?

[strictly]

Besides the obvious, no oil, broken oil pump, what are the other possibility. I'll explain the story first.

History

I have a 1967 911, with a 72' 2.4 Engine fitted. It has the 67 Oil tank, but on the back of the 2.4 engine it has an oil pressure SWITCH, not a sender as no pressure gauge in the 67 instrument cluster, just a light. The switch is brand new, more on that in a sec...

History of engine was unknown, car had not run in a few years, that is all that is known about it. It has not been rebuilt, but clearly has had some work (oil bypass mods are unknown). Car has been running for the last 18 months, but only for the purposes of moving it around, and except for the odd blast down the road, to check various things, like work on suspension etc (ongoing project). Has been started in the last month, maybe 20 or 30 times, driven round the block, etc

Car has had two oil changes, currently holding 10 litres of oil in tank, which is half way (on the 2.0 tank) when warm.

Yesterday i took it on its first 25 mile drive. Everything fine. Trans perhaps a little noisy, and yes maybe the engine a little noisy, but not alarmingly. Drove it a few times yesterday, all normal.

This morning on way into work, less than 1/4 mile from my house. Oil light flashes on . I immediately pull over, switch engine off and check the electrics. All seem okay, I try another wire to be sure (temperature sender, switched at gauge). Okay i call my buddy, he brings a KNOWN good mechanical gauge, and we take out the oil pressure switch and plumb it in (to #6 on diagram). Turn engine over, NO oil pressure, rev it to 3000 rpm quickly, still no oil pressure. Oh dear.

now remove oil pressure switch/gauge completely and no oil coming out of hole where oil switch is at back of engine (next to thermostat). Engine still sounds (normal) but i only run it for a second.

I'm going to start investigating to morrow, and just trying to gather ideas, before hand.



So questions? Or better suggest a fault finding path. I presume the first check is some how to see if the pump is moving? (i.e
I presume i can look down the bottom oil cooler hole into gears of oil pump, and turn engine over to check pump is moving.)

1. Can either the pressure relief valves (4 and 7) get stuck and close oil pressure off completely?
2. Can the thermostat restrict flow? or is this just the picture
3. In theory I should get the same (or similar oil pressure) tested either at the back of the engine where the oil pressure switch is, as tested at the front where the oil temperature switch is mounted?
4. Its the scavange pump which supplys the oil filter, so pulling off the sump cover (oil changed just recently) and checking the pick is clear, is a bit of a waste of time? (at least as a first look at the problem)

[boosted79]

Does it have an oil level gauge? If the oil pickup tube is blocked or came out of the scavenge pump then no oil will return to the tank and starve the pressure pump.

[strictly]

Hi boosted, no no oil level gauge. I have dipped the tank - half full when warm, and above the min mark when cold. Okay so checking the oil pick up in the sump is worth doing then.

Im a little confused on the exact oil level, as 2.4 with a 2.0 tank. I went for 10 quarts (no oil cooler down sills)

Presumably, if i drop the sump plate off, i should have quite a lot of oil in the crank case, as another indicator? That the pick up is blocked for the scavange pump

Im going to start working through this when i get a minute.

I think my first step is take the spark plugs out, disconnect the cdi, take things like the cam lines off/oil filter off one at a time to see if oil is moving, either by turning the engine by hand or on the starter motor only. Then put piece back on and move on to the next idea.

Followed by sump and oil cooler removal (i want to try and diagnoise as much as possiable with the oil system still full).

Do you think the oil pressure relief valves can have a big affect here, or am i most likely to be looking at a broken oil pump or something similar?

[boosted79]

Since you put a known good mechanical gauge in place of the press. sender and got 0 psi and then you also had no flow when you removed it why spend more time removing cams lines ,etc? There are three devices that could cause no oil at the sender location. Pump, safety relief valve (4) and normal operation press. regulating valve (7). I don't think the thermostat can shut off oil flow completely, it just diverts it through the cooler or around it, but while you're at it pull it out to check it for proper opening temp. Here's what I'd do:

1) remove discharge line at case from scavenge pump, crank engine with coil grounded to see if scavenge is pumping oil. You will get some oil draining out at first until line to tank is empty and case level drops to discharge line level. If no oil is pumping then pump not turning or scavenge suction blocked.
2) drain case and tank, remove sump plate to check scavenge suction line and screen.
3) if suction line and screen ok then remove feed line to pressure pump at case and see if you can observe the pump gears turning when engine turned over.
4) if above ok then remove the two pressure regulating valves to check for broken springs, stuck open, etc.
5) remove t'stat

I doubt that either of the regulating valves could cause no oil flow at all at the sender when removed which points to either pump or t'stat somehow blocking all oil from the pump if the pump is turning.

edit - actually press. pump feed line is on the oil cooler, not the case directly. probably hard to see if the gears are turning from there.

[strictly]

Boosted, thanks for that, really helpful.

Ok i will do just that (follow your procedure) and report back. Lets home something is blocked or stuck, but i very much doubt it!

as an aside comment. I once had a 911 where there never seemed to be that much oil in the oil filter when i changed it, but normally i would leave the engine overnight draining (case and tank), in that case would that have indicated that particular 911 possiably had problems on the scavange side or was it just conincedence because i let the oil drain overnight. I remember thinking the car was on the low ish side of oil pressure (i.e less than 10psi per 1000rpm). The guy that bought the car was aware, but even so i never quite figured out why the filter seemed empty

i'll report back in a day or two, going to get oily!!

[strictly]

problem solved!

the safety relief valve had the wrong spring in it, too long, ive put the correct 70mm spring in, and i have oil pressure. Motor sounds normal too. Phew!

p.s. i followed your procedure, thanks for that

[DRACO A5OG]

Phew! Dodge that bullet CONGRATS!

[bpu699]

Originally Posted by strictly

problem solved!

the safety relief valve had the wrong spring in it, too long, ive put the correct 70mm spring in, and i have oil pressure. Motor sounds normal too. Phew!

p.s. i followed your procedure, thanks for that

A longer spring should give you higher pressure, not lower. Puzzled?

[boosted79]

Strange. Maybe the valve was stuck open? Anyway glad it wasn't the pump.

[strictly]

Sorry i didnt give the full story, the piston was stuck, i managed to grip it and very carefully seem to have it working again, not sure what happened. There was also sludge, in both the tank and the oil sump. Not loads but way more than i expected.

The history of the engine is completely unknown, and what i think might have happened, is by driving it, i finally got it hot enough to open the thermostat and allow the oil cooler to work, perhaps this released some long built up sludge in the cooler, which managed to sieze the relief piston( or that was just a coniencndce).

Ive since done an oil and filter change, and will do again in another 50 road miles. Pressure is now really good, 100psi at 4000 psi cold (20w50). I didnt check it before as being a 67T it dosent have a built in dash prerssure gauge.

I also swapped the pressure relief valve springs, and perhaps confused the two terms. In any case ive got with the 70mm springs and all seems okay. Until the next drive of course! We'll see this next week.

P.s im sooooo relieved it wasent the oil pump, the plan was to drive it for a few months before throwing more money at it! Lol

[txhokie4life]

Good to hear....