Ok folks so I posted a few weeks ago about the oil filter light coming on. It seemed to go away after I did oil and filter change so thought everything ok, but it has come back now worse than before....

The key thing this time is I have noticed that if I reduce revs the light generally goes away for a while, so I am starting to suspect the strainer has a blockage.


Just had a quick look underneath and sump removal seems fairly straightforward, Allen bolts around the base and two bolts in to the gearbox, but do I have to remove that big radiator pipe or can I manage without, it looks very tight with two protruding parts above the pip!

Hope to start working on it tomorrow and so any tips would be appreciated!

Thanks

Oil pressure will generally increase with engine RPM and the sensor is simply a low threshold warning so reducing RPM shouldn't increase the pressure and the light extinguish.

 

I'd double check the wiring/have a poke about with the engine running whilst someone watches the instrument panel.

 

Consider having an actual oil pressure test.

Edited 21 May, 20215 yr by MicMac

1 hour ago, MicMac said:

Oil pressure will generally increase with engine RPM and the sensor is simply a low threshold warning so reducing RPM shouldn't increase the pressure and the light extinguish.

 

I'd double check the wiring/have a poke about with the engine running whilst someone watches the instrument panel.

 

Consider having an actual oil pressure test.

But doesn't returning oil rely on gravity, so if it was retarded by a blockage then the opposite would be true and the oil would sit in the top of the engine while it feeds down through the partially blocked  filter?

Edited 21 May, 20215 yr by Ollyk

The filter is on the pressure side, the oil drains freely within the crankcase once it has exited from the bearings etc.

 

There is also a strainer on the oil pick up pipe (the suction side of the pump) a blocked strainer would give exactly the symptoms that are being described.

@J.R.

Surely if the oil pressure meets the requirements at low RPM then higher RPM and hence pressure wouldn't cause a low pressure warning.

 

Unless the engine is shagged out, the oil type is incorrect, the oil level is low or there is some reason to suspect frothing.

 

Or am I missing some high tech digitally monitored system on VAG models that monitors oil pressure across engine RPM?

Yes JN sorry this is exactly what I think the problem is! Blocked strainer!

I believe it is a fairly common problem

MicMac, I guess it depends which side the pressure sensor is located? If it is upstream of the pickup and it is being starved of oil then it would be set off when oil was demanded?

10 hours ago, MicMac said:

@J.R.

Surely if the oil pressure meets the requirements at low RPM then higher RPM and hence pressure wouldn't cause a low pressure warning.

 

Unless the engine is shagged out, the oil type is incorrect, the oil level is low or there is some reason to suspect frothing.

 

Or am I missing some high tech digitally monitored system on VAG models that monitors oil pressure across engine RPM?

The pump output is proportional to the engine speed, the higher the revs the greater volume of oil pumped, a partially blocked pick up pipe strainer will pass enough oil at low revs but starve the pump at higher revs resulting in a reduction of output flow & pressure.

 

Also on my engine and probably all others of its generation there are 2 thresholds for the oil pressure warning lights one for idling and low RPM, one for higher RPM's the OP may simply be dropping beneath the threshold.

40 minutes ago, J.R. said:

Also on my engine and probably all others of its generation there are 2 thresholds for the oil pressure warning lights

I'm confused by that. There's only one oil pressure switch isn't there, so how can there be two threshold pressures?

 

 

@J.R.

I understand the proportionality of the oil pump output and that engine checks are generally made at both idle/low RPM and a manufacturer provided high RPM.  If both pressures are within spec the system is deemed good, however I was suggesting that if the minimum pressure was attained, why would the low pressure warning light?  The only way is for pressure to increase with engine RPM and to my knowledge the pressure sensor is either good/bad, it isn't measuring actual pressure, just that the minimum is attained.  Or are things more complex nowadays with the oil pressure being monitored across all engine speeds by the ECU?  If so I can understand how a restricted feed would starve the pump and hence flow, triggering a low pressure warning.

Wino, I will have to go through my self study guides again, I'm pretty sure that I didn't imagine it, I dont think there is a pressure transducer so that would mean two pressure switches, maybe I did dream it.

 

Mac, with a partially blocked strainer up to a certain RPM the pump output will not be significantly affected but once there is starvation on the inlet side cavitation will occur and the output flow will remain constant or even drop and the pressure will drop.

 

When I dry sumped my X Flow engined Westfield I used solid metal hydraulic pipes along the chassis & fixed parts, tank, thermostat, filter housing, cooler etc & braided lines to the 5 port pump, the lines were not big enough and I had to keep the revs low until the oil had warmed through and the viscosity dropped because the  oil pressure would fall above 2K rpm, it gradually got higher as the oil warmed.

@J.R.

I get the cavitation bit so we will see what the OP finds when the sump comes off, hopefully they will photograph any findings.

ok folks sump came off fairly easily in the end (just two bolts on the clutch side a PITA) and there were bits in the strainer mesh...

Soo I just gave it a damn good clean with my jet washer, removed all traces of old oil then heated it to get rid of any water. Went back in and everything has been fine since!

Fingers crossed it will be ok... To be fair I had been overdue with an oil filter recently so lesson learnt there...