Having read a few tales of oil light issues on the forum, I've still not been able to figure out my own issue.  2011 htp 1.2, owned 11 years, 120k miles, full service history, last serviced/mot a week ago.  Looks like it has spent most of its life being used for target practice on a tank range, but has been mechanically loved!  A week or so before going in for service, we started to get a random (?) three flashes/3 bongs from the red oil warning symbol on the pack. 

 

No apparent pattern in terms of speed/cornering /temp etc, no apparent issues at tickover, where I would expect low oil pressure to show up, and no issues with tappet or camchain tensioner noises.  Filter removed during service is in good condition, oil levels were on max.  Sometimes it will go 5 miles and fault, sometimes 30+ miles.  Oil + filter at the service made no difference - fault still present.  Should probably point out at this point that the timing chain was swapped out and the head rebuilt 12 months ago, and the sump, oilways etc were cleaned out at the time. Engine is suitably "oily" up top, and has probably done c.100 miles with this issue, so I dont think its a "real" problem.

 

Swapped the pressure switch, and replaced the connector and harness tail, suspecting an intermittent open circuit, with no improvement.  There are no other known electrical issues on the vehicle.

 

If I've understood correctly, the sequence of events on start up is as follows:

• Ign key on, pack does self test, oil light goes out.
• Crank/start engine, oil pressure switch closes to ground, pack starts to monitor switch over approx 1800 revs.  (Ref the comment regarding no low oil pressure warning at tickover, does anyone know if the pack continues to monitor once "triggered", or does it always ignore the oil pressure switch at low revs?)

 

In an attempt to seperate engine issues from wiring issues, I've run with the oil switch disconnected, and the pack throws up a continuous oil pressure warning when revved over tickover after starting, so that appears to confirm that the pack is ok.  I've also run with the oil pressure switch wire grounded at the engine, thinking that this is what the pack is expecting to see, and any further alarms would indicate dodgy wiring, but with no further false alarms.  (I did wonder if part of the self test routine actually looked for the change of state on the pressure switch on start up before activating monitoring, so I'm not entirely sure that this test is valid - open to others experience on this one!)

 

Appreciate this is a bit wordy, but wanted to try and capture everything I've done so far.  Any suggestions other than holy water or a gallon of petrol?

TIA 

Steve

I thought there were two oil pressure sensors, if so then you've changed out the good one for a new one.

Just one pressure switch. Where did you buy the replacement from? 

I thought the rpm threshold was 1500, and I don't think the cluster (pack?) ever monitors the switch state below that, except perhaps during cranking.

Edited 5 March, 20242 yr by Breezy_Pete

Pete

Correct, just one oil pressure switch.  Replacement came from a local Europarts store, and was a branded component. 

 

You may well be right about the 1500/1800 rpm switching point, (I was working from memory!), but I guess as long as the oil switch has closed before the pack reads that engine speed, the logic should be satisfied and the light should stay off?

 

The bit I'm struggling with is the apparently random and intermittent nature of the fault - next step is probably to put a pressure gauge on the engine and see what's happening there, but I'm guessing that if the "blip" is intermittent, I'll be lucky to see anything. 

 

My other thought was to replace the oil switch with a conventional oil switch (open under pressure), wired through to a led and buzzer in the car, so that I can monitor the oil pressure indipendantly of the vehicle wiring.

 

 

Pressure gauge sounds like a good plan. Look to see if pressure is close to the switch rating, especially at just above 1500rpm, with engine at full temperature. 

Will report back in a few days when my gauge arrives!

Update time.  Gauge arrived today, more investigations carried out.  Got the engine warmed up prior to testing.

 

1 - Using a continuity checker, new oil pressure switch was open circuit on tick over, and closed reluctantly at around 1800 revs.  I guess this confirms that the car ignores the oil pressure switch under 1500 rpm, as suspected, and also that my tick over oil pressure isn't too good.

 

2- Pulled oil switch and fitted the test gauge.  Tick over pressure was next to nothing on the gauge, too low to accurately estimate it (fraction of a bar).

 

3- Increased revs to 2000, pressure slowly increased to 1 bar (15 psi).  3000 rpm didn't make much difference.  Believe the spec is about 2 bar at 2000?

 

Strangely, the tappets and the cam chain were quiet all through this process.  I guess the question now is is it the oil pump/ relief valve, or is it worn crank bearings? Is there an easy way to differentiate?  I'm inclined to think a crank would be noisy, but I'll take opinions on that one! (Maybe a bit of wear on both?).  FWIW, the car has done 115k miles, but has a full service history from our local indipendant.

 

Has anybody done an oil pump change, and if so how many hours labour should I be looking at?  Also, can it be done from underneath by just removing the sump, or does the timing side have to come apart as well?

 

Final point, if anybody is looking to buy a cheap oil pressure test kit off ebay, avoid the ones with a pressure relief button in the base of the gauge - mine sprayed hot oil all over my hand when pressed.

This makes no sense, if you really had no oil pressure on tickover then the engine would have self-destructed long ago, there must be a flow restriction somewhere upstream of the pressure sensor tap.

Is this engine definitely a 1.2 htp 3 cylinder? Engine code? Are the small O rings on the end of the long bit of the plastic filter housing cap still present? Items 16 and 17

 

 

 

Not a 1.2tsi 4 cylinder? (Thinking of the O seal left behind scenario)

Edited 8 March, 20242 yr by xman

There is virtually no oil pressure at tickover, measured at the switch - the gauge reading and the operation of both the original and the replacement oil switches confirm this. If there was an upstream restriction, any idea where to check?

 

Its deffo the 3 cylinder htp!! I'll check the o-rings, but the car started doing this 10 months after its last service, with no intervention, so unless it was some sort of "delayed effect" (can that happen?).  What purpose do the o-rings serve?

 

Thanks all

Steve

18 minutes ago, SG10 said:

What purpose do the o-rings serve?

They seal the supply pathway from the filter to the oil galleries that lubricate the engine, without them you'll lose pressure and flow especially at idle.

 

Maybe been damaged/torn during filter service and/or dropped off or some numpty removed them and didn't replace them. Or maybe not sitting in the correct position on the stalk. If missing then check not gone somewhere where not supposed to.

 

The green items in the photo

 

Edited 8 March, 20242 yr by xman

Xman

Thanks, I'll take a look at these.  Can I get away with just unscrewing the cap, giving it a minute to drain down, and pulling it out, or do I need to do a full oil drain first?

No need to drain the oil. As you've said, just unscrew the cap and wait 30 secs before lifting it out. Have some paper towel underneath to stop oil dripping on the alternator and belt.

 

A large white O ring above the threaded part sits in a channel above the threads on the outside. So three O rings in total.

 

 

Edited 8 March, 20242 yr by xman

39 minutes ago, xman said:

They seal the supply pathway from the filter to the oil galleries that lubricate the engine, without them you'll lose pressure and flow especially at idle.

 

Maybe been damaged/torn during filter service and/or dropped off or some numpty removed them and didn't replace them. Or maybe not sitting in the correct position on the stalk. If missing then check not gone somewhere where not supposed to.

 

The green items in the photo

 

 

Good on you! 👍

Thanks, Xman!

Appreciated!

Pulled filter housing, o-rings were in place and looked to be OK.  They are both stood slightly proud of the groove on the stick, and do not feel hard.  I reckon these are ok(?).

 

Out of interest, does anyone know what the black rubber/plastic jobbie is in the base of the filter housing? 

 

Having done all of this, and out of curiosity, I then rechecked my oil pressure switch with the engine cold, and it was behaving itself, suggesting that I have more acceptable pressure on a cold engine. Didnt connect the gauge to collect numbers - maybe I should? I guess this explains why my camchain and tappets are quiet on start up, and possibly why I haven't scrapped the engine yet?

 

Thinking this through, maybe the question now becomes why does my oil pressure drop off sometimes, but only when my engine is hot - anything between 5 to 15 miles driving?

 

To reiterate, it has done this pre and post service, has the correct grade of oil and a decent filter.  The failure pre service was around 10 months after the last oil and filter change, not immediate.  The oil pressure switch has been changed for a new (branded) part, and its behaviour corresponds with the readings on the oil pressure gauge.  Filter housing seals look good, and there are no obvious leaks anywhere.  Anticipating possibilities such as crank wear, the bottom end sounds quiet - no rumbles or knocks. Vehicle has been regularly serviced.

 

Pressure relief valve, possibly? I assume its integral with the oil pump?  If so, what's the labour time look like to swap it out?

 

TIA

Steve

 

 

Today's latest.  I was curious about the cold oil pressures, so I fitted the gauge to the head to see what was going on.

 

Initial cold oil pressure was over 2 bar, but fell to around 1 bar by the time the blue low temp light went out.  Corresponding 2000 rpm figures were 3.5 bar cold, 2.5 bar "warm".  So far, so good. 

 

Reconnected the oil pressure switch and took it for a drive.  At around the 5 mile mark, I could get the oil light to come on by holding the revs just above 1500. Raising the revs to around 1800 extinguished the oil light and kept it off.  I'm now realising that this behaviour is repeatable and reproducable if you avoid switching off the oil pressure monitoring light by letting the engine drop below 1500.

 

Looking like crank wear perhaps?  Time to buy a gallon of 10/40?

Maybe get it on VCDS, to look at what coolant temperatures actually are when the engine is fully warmed up? Might be running hotter than it ought to be, without triggering any warnings. 

1 hour ago, Breezy_Pete said:

Maybe get it on VCDS, to look at what coolant temperatures actually are when the engine is fully warmed up? Might be running hotter than it ought to be, without triggering any warnings. 

Sorry, pressed the wrong button!

 

Don't have vcds access, unfortunately.  Might it be worth forcing the fan on with the aircon, perhaps, to give some extra cooling?

Could be an interesting experiment,  if the A/C works. 

Can you not do the same test with the oil pressure guage connected?

 

Do you know what the switch point of the oil pressure switch is supposed to be?

 

You really need to know that, I am guessing 1.25 or 1.5 bar, you need to know what the oil pressure is when the light is coming on.

 

Being a little low is not an issue if it continues rising linearly to the pressure relief limit by say 3K rpm at normal running temperature (so you also need to know what that is) a lighter grade oil will give lower pressure but putting a thicker oil in is worse for the engine especially when cold.

 

Modern engines with crankshaft driven oil pumps (is yours) running thin oils do not develop such good pressure at low RPMs where it is not needed but flow huge amounts of oil at higher revs, if the PRV sticks the pressure can go through the roof, my 1.8 Zetec race engine (early pre production engine befire the PRV recall) blew the filter O ring out sideways on the starting grid at Lydden Hill.

Pete - perhaps surprisingly, the aircon works a treat, and has never been regassed in 117k miles!

 

JR - thanks for your thoughts.  Oil pump is chain driven off the crank end.  Ref one of my earlier posts, hot engine oil pressure doesn't rise much above 1 bar at 2000 rpm, and barely increases any further at 3000.  Oil pressure switch is, I believe, specified 0.3 - 0.6 bar (5-10 psi, ish?), and system should be around 2 bar @ 2000 rpm, with a 5 bar max. 

 

Fwiw, I was only joking about the 10w40!!  

 

I'm scratching my head over whether this is most likely a worn crank, worn oil pump, a stuck pressure relief valve, or if I've missed something else.  

If your crank shells were toast you'd hear the rumble but you can check by removing the sump and one of the main bearing caps to visually inspect the half shell. Although I'd expect the sump to be full of glitter.

2 hours ago, SG10 said:

JR - thanks for your thoughts.  Oil pump is chain driven off the crank end.  Ref one of my earlier posts, hot engine oil pressure doesn't rise much above 1 bar at 2000 rpm, and barely increases any further at 3000.  Oil pressure switch is, I believe, specified 0.3 - 0.6 bar (5-10 psi, ish?), and system should be around 2 bar @ 2000 rpm, with a 5 bar max.

 

Thanks, I was working on the cold pressure readings.

 

A worn oil pump usually manifests itself with taking a long time to prime and knocking on start up, it sounds like a foreign body between the PRV plunger and its seat or a damaged seat, that would explain the increased pressure drop when oil is hot.

 

Another possibility, was there any engine work done before the drop in oil pressure? There are often restrictors to limit the oil flow through the cylinder head and OHC valve gear, on some engines they have been a metering hole in the head gasket which either blocks with carbon starving the cam followers (happened on my SJ410) or fitting a pattern part gasket with a bigger hole results in oil pressure drop. There can also be restrictors to limit oil flow to piston cooling jets, a leak from the timing chain tensioner is also a possibility.

 

I have just noticed that you wrote:

On 05/03/2024 at 17:35, SG10 said:

the timing chain was swapped out and the head rebuilt 12 months ago, and the sump, oilways etc were cleaned out at the time.

 

Maybe something fitted has failed, a crack in the tensioner housing. It happened before the oil change so not that and you have checked the filter O rings, oil pumps usually wear very slowly so I doubt it is that unless something is preventing the PRV from properly sealing, back in the day we would grind them in.

 

I dont think it is a blocked pick up pipe guaze as the oil pressure would increase when hot not decrease and when cold it would decrease with revs.

 

I believe oil is being recirculated and not getting to the main gallery in sufficient quantity to create the normal backpressure so either the PRV (my gut feel) or an enlarged orifice or cracked timing chain tensioner housing.