What does the Oil pressure gauge try to tell me?

[sub_zero]

Hi all,
The oil pressure gauge on my dash is at 3 when the engine is cold and goes down to 2.75 or 2.5 max. when the engine is warm or hot.
Nowadays weird something is going on,the oil pressure gauge goes beyond 2 and today for the first time I see the gauge at 1.
I think the gauge is trying to tell me something,but I don't know what.
Generally,I see the oil pressure gauge on older models of MB,it is no longer available in newer models.
What is this gauge made for?
Does it help diagnose the oil pump? what would go wrong with the oil pressure?
My car is W124 ,E220 engine type 111.
Your help is much appreciated.

 

[television]

The gauge does what it say, and they were used to give an indication of the condition of the bearings in the crankshaft in particular. The oil pressure is always higher when cold as the oil is thicker. As long as its at least 2 when you are driving thats fine.

Maybe an oil change is due

 

[stevesey]

A sudden change like that could be an indication of something serious. How does the oil pressure change between idle, 1000rpm, 2000rpm (when hot)??

 

[sub_zero]

When driving it is always 3 bar,when at traffic it is at 2.75 when hot(still engaged),this was the normal mode for years.
Nowadays the gauge at 3 when driving,drops to 2 when at traffic (still engaged),but today it dropped to 1 bar ,that is why I decided to consult you .
Maybe you are right about oil change,this is the first time I exceed 5000km,I used to change oil every 3000km in summer (it is very hot here in Kuwait) and every 5000 km in winter,this time I'm almost 6000km .
I will change the oil,observe the gauge and I'll let you know.
I have read alot of threads about oil pressure gauge and its readings,the normal reading is between 1.5 and 2 bar,which has never happened to me,my gauge normal reading was between 2.75 and 3 bar,even when engine was hot.

 

[television]

A sudden change like that could be an indication of something serious. How does the oil pressure change between idle, 1000rpm, 2000rpm (when hot)??

We do need to know if the 1 was at idle, if the car was very hot it can drop down to this on idle

 

[sub_zero]

when hot and idle,the reading is 1 bar (today is the first time to read so).
When hot and 1000 rpm,it is 3 bar.
when hot and 2000 rpm,it is 3 bar.
so just when I accelerate the gauge goes up to 3.

 

[television]

when hot and idle,the reading is 1 bar (today is the first time to read so).
When hot and 1000 rpm,it is 3 bar.
when hot and 2000 rpm,it is 3 bar.
so just when I accelerate the gauge goes up to 3.

If its at 3 at 1k then it is OK there are no quoted figures for idle.

With modern oils sludge is a thing of the past, its possible that the camshaft for instance has cleared itself of a old blockage and that would show on idle

 

[stevesey]

That looks good to me as well (someone with a 111 might be able to report what pressure they get at idle), but if it climbs quickly from idle to 3 bar that seems pretty healthy.

N.B At 3 bar the pressure relief valve cuts in to limit the pressure (otherwise it would carry on climbing with increased pump speed).

 

[Ian B Walker]

According to the book Oil pressure of 0.3 bar at tickover is the basic minimum open the throttle to 1500 rpm and it should read 3 bar. However I would rather suspect that your main bearings may be slightly worn. Nothing to fret about at the moment but something to keep your eye on. My ex 260E used to tickover at 1 bar when hot. It did this and is still doing this after 237,000 miles.

 

[sub_zero]

Sorry Ian but I don't get you,what do you mean by tickover?
What do you mean by main bearings?

 

[television]

Sorry Ian but I don't get you,what do you mean by tickover?
What do you mean by main bearings?

The main bearings are all part of the main oil pressure in the engine along with the big ends, this is the most important part of the engine, there is a small oil way up to the top of the engine lubricating the valve gear.

Tickover is Idle.

 

[jaymanek]

Its normal, dont worry at all... As long as oil pressure is 3 when driving, no need to fret.

Just keep oil changed every year or 10K and all will be fine..

 

[Dieselman]

The main bearings are the ones that the crankshaft runs in. The piston connecting rods are connected to the crankshaft via the big end bearings.

Just clarifying Tv's post.

Oil pressure is usually a good indicator of the amount of wear in these bearings, more pressure = less wear.

As Ian says you don't really need any pressure at idle as the engine is under very little load and there is still oil flowing.

If there is significant wear it will take a while for oil pressure to build after a cold start.

 

[television]

If there is significant wear it will take a while for oil pressure to build after a cold start.

Not so, the oil pressure will be at max when cold, and will fall off rapidly as the oil thins when it gets hot.

 

[Dieselman]

Not so, the oil pressure will be at max when cold, and will fall off rapidly as the oil thins when it gets hot.

Hmm..I don't want to get into an argument here, but if the big ends and mains are worn they will release all the oil in them overnight and it will take a while for the pump to replenish this once the engine is started again.

It can take some while for pressure to build up again due to the oilways being drained.

 

[television]

Hmm..I don't want to get into an argument here, but if the big ends and mains are worn they will release all the oil in them overnight and it will take a while for the pump to replenish this once the engine is started again.

It can take some while for pressure to build up again due to the oilways being drained.

Almost instant, 3 seconds, thats the max time that I have ever heard a knocking

 

[sub_zero]

All that is indicated by the oil gauge pressure,I wonder how would an ordinary car driver understand this gauge?
No wonder this gauge was removed from newer models,it is absolutely technical gauge.
Maybe it is useful if you want to buy a second hand car,this gauge may help determine the condition of the engine,whether it needs overhaul or not.
Concerning the wear in the bearings,this means I will eventually see smoke coming out of the exhaust? and oil level will get low every once in a while?

 

[television]

All that is indicated by the oil gauge pressure,I wonder how would an ordinary car driver understand this gauge?
No wonder this gauge was removed from newer models,it is absolutely technical gauge.
Maybe it is useful if you want to buy a second hand car,this gauge may help determine the condition of the engine,whether it needs overhaul or not.
Concerning the wear in the bearings,this means I will eventually see smoke coming out of the exhaust? and oil level will get low every once in a while?

Smoke is something else and that happens when the pistons/rings/valves are worn. smoke while accelerating is rings, smoke after standing at idle is valves.

The bottom end as its known thats the crankshaft and big ends.
Years ago we only ever bought a car if the oil pressure was good. I even used to modify the oil pressure gauges on Jags as they always read low, but people did not like it.

Modern engineering has moved on from the 50's where the max of 25k miles was the max for a Ford 8 engine. Our cars go many hundreds of K miles now and no one ever does much to the bottom end of a car these days.

 

[sub_zero]

Smoke is something else and that happens when the pistons/rings/valves are worn. smoke while accelerating is rings, smoke after standing at idle is valves.

The bottom end as its known thats the crankshaft and big ends.
Years ago we only ever bought a car if the oil pressure was good. I even used to modify the oil pressure gauges on Jags as they always read low, but people did not like it.

Modern engineering has moved on from the 50's where the max of 25k miles was the max for a Ford 8 engine. Our cars go many hundreds of K miles now and no one ever does much to the bottom end of a car these days.

Thanks television,that was really informative.

 

[sub_zero]

Why not it is the oil pressure sensor that sends to the gauge?