Gauge shows low oil pressure, but....

[lsmalley]

So my oil pressure gauge shows I have low oil pressure. I have a brand new sensor I just put on last week (problem was present before that) and it still shows low. I ended up removing the valve cover, because I remember I did that once and started the engine and a bunch of oil shot out all over the exhaust manifold and engine bay. That time there was no issue with the oil pressure. I did the same thing just to see if I was still going to see that sort of pressure and yes, the same thing- oil everywhere, but I was prepared for it this time. I currently have another m103 on the engine stand now and I'm examining the oil pump on that and can't see how this thing could possibly fail even a little. There is an extremely sturdy and solid mesh armour that prevents anything larger than maybe 1mm or so from being sucked up by the pump and also just by looking at it, if it fails it would seem that there would be no oil at all. Starting the engine first thing, the oil is normal and pressure seems fine, but after about 20+ minutes it drops by about 1 bar, then after about 30 minutes it will completely drop or nearly be resting on the peg. I may be missing something because even resting on the peg at idle, there is oil going everywhere. I let it idle and looked through the oil cap opening (valve cover back on) and could see a steady stream of oil pouring from the top camshaft oil pipe and when given acceleration the oil increases and begins flowing at greater force. I checked the connection of the readings from the pressure sensor and those are correct as well (e.g, 1 bar=63-76 ohms, 2.5 bar=148-167 ohms, etc). So what am I missing?

[porkface]

replace the sensor with a mechanical gauge and try again. see if the numbers agree. with the wire off the sensor, turn key on and ground the wire. the gauge should max out. haven't worked on a 103 in a looong time but i don't remember any oil pressure problems-ever.

[oldsinner111]

Hope it was german sensor, and not cheap
.

[lsmalley]

Originally Posted by oldsinner111

Hope it was german sensor, and not cheap
.

Limited control on where the German companies have their manufacturing plants. Last one was Meyle, which was made in Germany, this new one is Febi-Bilstein made in Taiwan 🙄. I will order the quality brand, but the parts comes from various places. At any rate this engine has a little over half a million miles on it, I just found something about an oil pressure relief valve. If the valve is stuck open it apparently can cause low oil pressure. I need to drop the oil pan in order to check it. I'll pull the one I have on the engine stand off and see how it looks because I'm not sure how to test it. Also, since I need to drop the oil pan I will need to buy a gasket and probably new motor mounts while I'm at it.

[oldsinner111]

wow, never thought how about dash gauge?

[lsmalley]

So after looking at the set up of the oil pump, I came up with this:

1) Previously the plastic chain guide railing broke and was broken into small pieces.

2) I removed most of these pieces, but a small piece was likely pulled into the pump through the oil galley circled in the picture due to the close proximity of the railing and the galley opening.

3) As the pump moves the oil and forces back the pressure valve the piece probably went past the plunger and is lodged between the plunger and where the plunger rests against the back of the passage, thus keeping the pressure valve stuck in the open position.

4) As the car sits for a while the oil slowly flows back down to the pan and allows the plunger to close a bit more, but not fully due to the piece that may be preventing it from fully closing. So when I start the car up again after it sat for a while the oil pressure will initially be up again until the valve starts to fill and the additional oil and the possible broken piece of railing cause the valve to open more than normal, thus dropping the pressure of the oil.

This is of course just a theory based on the symptoms, which is only the low pressure reading. I suspect that these cars will put out well over the amount of oil than what is required to keep the components lubricated. 3 bar is about 44 psi to begin with and that can be achieved at about 1500 rpm, so I wonder what the pressure reaches at 4000 rpm. Anyways, once I get the oil pan gasket, and probably the mounts, I'll drop the pan and see if this is indeed the issue. Also, I did test the cluster gauge with an ohmmeter and everything is working as it should.

**Edit**By the way, note the mesh filter at the opening of the oil pump. It feels like heavy duty chain mail. I understand now why the plastic railing was used: to prevent catastrophic damage to the engine components same as the plastic ends on the radiator. I found the later out when my engine reached about 120C while I was unable to pull over or shut it down and I heard this loud explosion under the hood. The radiator plastic had over pressured from the high temp and coolant was everywhere.

[altezza]

https://www.classicjalopy.com/2021/02/m103-oil-pump-catastrophic-failure/

[oldsinner111]

wow man. I heard either m103 or 104, you can go with a diesel oil pump, pump higher pressure, and indestructable.

[lsmalley]

Originally Posted by altezza

https://www.classicjalopy.com/2021/02/m103-oil-pump-catastrophic-failure/

Very interesting. He seems to have done all the same steps as I have as far as troubleshooting, except for the mechanical gauge. However that type of failure seems extremely uncommon. Thanks for sharing this.

[Duke2.6]

Originally Posted by lsmalley

So my oil pressure gauge shows I have low oil pressure.

So what is your definition of "low oil pressure"? I recall reading that idle oil pressure down to about 0.3 bar is okay, but I rarely see less than 1.0 on my 190e 2.6 five speed(idles in neutral at 700), and it pegs the 3.0 max gage reading by about 2000.

It drives me nuts on these automotive forums when guys say my car "overheats" or has "low oil pressure", but rarely if at all ever mention actual readings from their dash gage and the driving and ambient temperature conditions at the time.

Duke

[lsmalley]

Originally Posted by Duke2.6

So what is your definition of "low oil pressure"? I recall reading that idle oil pressure down to about 0.3 bar is okay, but I rarely see less than 1.0 on my 190e 2.6 five speed(idles in neutral at 700), and it pegs the 3.0 max gage reading by about 2000.

It drives me nuts on these automotive forums when guys say my car "overheats" or has "low oil pressure", but rarely if at all ever mention actual readings from their dash gage and the driving and ambient temperature conditions at the time.

Duke

Well my definition of "low oil pressure" would be anything below the specified ranges by MB. I have the fsm spec sheet for the engine temp and what the readings should be for the corresponding temp and oil pressure and mine is definitely below that, but I haven't confirmed what's causing it yet. As I've mentioned the oil is definitely getting "some" pressure, but probably not what is recommended. Once I'm able to drop the pan, I'll be able to post the findings and the solution hopefully.

Originally Posted by lsmalley

Starting the engine first thing, the oil is normal and pressure seems fine, but after about 20+ minutes it drops by about 1 bar, then after about 30 minutes it will completely drop or nearly be resting on the peg.

[porkface]

Originally Posted by altezza

https://www.classicjalopy.com/2021/02/m103-oil-pump-catastrophic-failure/

never seen a pump come apart like that before, any make, period.

that would also never have pressure at any temp, so i doubt the op has this same problem.

[Duke2.6]

Originally Posted by lsmalley

Well my definition of "low oil pressure" would be anything below the specified ranges by MB. I have the fsm spec sheet for the engine temp and what the readings should be for the corresponding temp and oil pressure and mine is definitely below that, but I haven't confirmed what's causing it yet. As I've mentioned the oil is definitely getting "some" pressure, but probably not what is recommended. Once I'm able to drop the pan, I'll be able to post the findings and the solution hopefully.

How about telling us what the actual NUMBERS are.

Duke

[lsmalley]

Originally Posted by Duke2.6

How about telling us what the actual NUMBERS are.

Duke

Fluctuates....sometimes it's 2 bar. After driving for 30 minutes it could drop to 1 bar or it may just stay at 2 bar. At the next start up it may start out at 1 bar and then drop to .3 bar or just hit the peg and stay there. After a bit more researching, the pressure valve theory seems less likely though, since a friend pointed out that it could be a worn connecting rod bearing. I Then heard the knocking noise as I revved the engine up. I was told that the widening between the bearing reduces oil pressure since you now have the unchanging amount of oil flowing through a larger gap than a smaller one. If this is the case in order to change the rod bearings one of 2 things need to I happen I thing: I can either remove the crankshaft to access both halves of the bearings or I can remove the head to remove the piston to gain access to both halves of the bearings.

[porkface]

pull the head and the oil pan. that will get access to the rods. pulling the crank is the hard way.

i would pull the pan first and remove the lower caps from the rods. then you can see the bad bearing.