Oil lamp question

[silverDH]

Hi
I have a 1.2 2005 Polo 9N1. Whenever coming down from a Highway with the engine properly heated up, thermostat holds it at 90*C, the oil sensor and buzzer come on for 10-20 seconds and then stop and comes on more often on slow roads. This mostly happens on hot weather and I've been driving it like that for a year now, nothing bad happened... so far. Changed the oil yearly Castrol EDGE 5W30 and filter, no gunk on the filter, new oil pressure sensor... didn't go into the sump and pump parts and all so I would like an opinion before going there, also, let's say there's no electrical fault and it's a mechanical problem, being the more likely cause of wear, but I could be wrong. As a side note, I went to a Skoda dealer, official VW service in my country, and they were assholes. They told me the chain makes noises, later a different mechanic said it's not the case, nor was it mine, I know how a worm chain sounds like and this engine is pretty quiet overall. Then they said they found shavings in oil, and that I needed a new chain, how exactly I don't know,they never opened the sump, not even the oil filter, and as I recall metal doesn't float in oil to be picked up on the dipstick, since that's about the only thing they looked at, which then led to the chief mouthing off at the mechanic to stop the oil pressure test because the timing chain might break and they don't want to be blamed so I never got to see the actual pressure on the VAG tester. Overall a poor experience from what was supposed to be a "professional job", but that's that, for the moment official shops are off limits, moving on. And now I'm on the internet getting some clues what's going on before taking the car to a local mechanic.


I would think it's gunk in the sump and when the oil gets hot enough the gunk gets loose and sucked into the pump's intake, what boggles the mind is why it recovers if higher revs are applied for a prolonged time. On trafficless roads I can drive it for hours and not get the issue... but most roads are not like that.

[niall campbell]

you need a scan as it could be High or Low pressure, two separate sensors


Do you have to top up the oil ?

[silverDH]

Thank you for answering... you're the 1st on many forums to do so.

About a year ago I had the oil sensor changed, an inexpensive one, located on the right side of the engine block around the area of the 1st air intake hose.
14 - 0.3…0.7 bar oil pressure switch -F1-, 25 Nm (http://workshop-manuals.com/volkswagen/polo-mk5/power_unit/3-cylinder_injection_engine_(2-valve)/engine_cylinder_head_valve_gear/cylinder_head/assembly_overview/)
Before that the mechanic did read the errors noted something on a paper and said an oil pressure sensor needs to be replaced, after which the cleared the log.
At a later date I had another scan but nothing came up even though the warning light came on multiple times in between the scans, so I don't know about the 2nd pressure sensor.

Oil level is at max.

I was thinking it's something in the line of, since the issues comes up when the engine gets hot, but maybe I'm wrong:
33156

[Rob69]

You dont say what mileage is on the engine but I suspect you have worn bearings or oil pump, when the oil is at maximum temperature (minimum viscosity) after a high speed motorway run and the engine revs are low the pump is struggling to provide enough pressure , due to excessive bearing clearances or worn pump internals. Revving the engine clears the warning and buzzer -yes? Also check the engine is not overheating, dont rely on the dash gauge as they are very inaccurate, radiator fan kicks in and out ok?
It could be the sender unit but you need to confirm the pressure with a gauge, at cold and hot engine and various speeds. What you do next depends on how much you want to spend vs. Value of the car. You could try a 15/40 or even 15/50 oil to give higher viscosity at high temperatures as a temporary measure as bearing or oil pump work will be expensive.

[silverDH]

The car has about 100k mi. I've tried with a thicker oil, 15W40, no change, or a bit worse on slow roads.
Revving it doesn't clear the buzzer, it clears itself after a while, 10-20 sec, regardless of revs. I can drive it with low revs and it won't buzz, not until I go high for a while and then come down to very low.
As for the radiator fan, I've never heard it kick in, but then again I've never seen the engine go past 90*C nor after opening the hood did I feel excessive heat, more than normal.
The engine runs pretty smooth, that's why I wanted to ask a bit before diving in doing expensive work.
As for that high pressure switch, where would it be located?

[Rob69]

You need to run it with a pressure gauge to confirm true oil pressure. Don't rely on the dash gauge, true engine temp can be higher or lower than 90 but the dash gauge stays at 90. Plug in an OBDII diagnostic tool that will give you true indicated engine temp. I'm not aware of a high pressure switch, maybe Niall will be back to answer that as he runs one of these engines in a polo.

[niall campbell]

the only way to really check is indeed a Pressure check or Compression check

The valves & oil sealing ring on each piston are prone to failure, my boys car had the oil piston rings stuck in each cylinder


If your burning oil, then go for compression check first. An acceptable allowance of oil used in most cars is from Max to Min on dipstick between services, 10,000 miles. However plugs and coils is every 18,000 on your car so .................. that's 9,000 every oil service

[niall campbell]

and go to VW for a genuine oil pressure switch for engine. The other one is in the dash I think, that makes it monitor below 30 psi if memory serves correct. The low one does 0.40 to 0.60 bar ............... that's 5.8 psi to 8.7 psi