oil pressure + oil level = panic?

Hopefully not a numpty post but I have creeping concerns.

Oil pressure at start up is at 3 but say on a cruising motorway drive eg 80mph in 5th it will by c 2.8. Hot idle is 1.25 which is lowish to me. Also there's a short decline off the main road to our drive and as I drive down this can drop to 0.5 before settling back to 1.25. So must be an oil level issue? From cold the level is obvious and is slightly over max. However doing the oil check by the book it's much more difficult to determine as the oils more viscous and "lighter" and I don't want to overfill. The coupe appears to be running ok - starts first thing, ticks over fine with no unusual noises and can't see any smoke etc in my rear view mirror. It's been through the capable hands of AllItalia and Motormech since May and no issues have been highlighted and a compression test returned solid results. Any observations peeps?

One way to reassure yourself is to carry out a mechanical oil pressure test. You can get this equipment at places such as Machine Mart for around 40 quid if you want to do it yourself, otherwise get your friendly spanner-man to do it.

I tried doing this myself on my Porto 20vt, I didn't find it was that straightforward, never having done it before. The procedure is to unscrew the low oil pressure warning sender and screw in the gauge. Start the engine and let it warm up until the fans come on, and see what the dash gauge shows at hot idle conditions. Then switch off the engine and press the "release" button on the external gauge to drop the pressure reading to zero (some oil will likely leak out at this point) and restart the engine and leave it at idle, noting the readings on both gauges. Then increase the revs in steps, say to 1000, 1500, 2000, 2500, etc. ...easier said than done if you are holding the external gauge and a notepad and pen whilst looking at both gauges and trying to keep your foot steady on the pedal...

On the 20v/20vt engine the spec is pressure when hot (oil T 100°C) at idle should be > 1 bar and > 4 bar at 4000 rpm (but dash gauge stops at 3 of course). On the 16v/16vt engines the spec is 0.8/1.1 bar at hot idle and 5/5.5 bar at 4000rpm.

How long has the oil been in there, when was it last changed (what date, and how many miles ago)? What's the engine mileage?

Low oil pressure can be caused by worn bearings (eg: big end), worn oil pump lobes, problems with the pressure relief system, and dilution with petrol from leaking bores/rings/injectors - try a "sniff test" on the oil, does it smell like oil or does it has a faint whiff of petrol?

On a 16v, I believe the largest oil pressure loss on a high-mileage engine is from the bearings on the balance shafts.

One and a quarter bar is probably to be expected for a hot high-mileage engine.

Thanks peeps for the above. The coupe has had 2 x oil changes since May and has got 107k on the clock which isn't that high on a 24 y o car. Although it is in regular use the journeys tend to be short ie 14 mile round trip to work. If I had some of the mechanical problems above then surely the running of the car would be getting compromised?

Sounds about the same as my 16v which I drive every day - if that is any help - I have an oil leak towards the front of the engine down low so I top up regularly. Once it is back on the ramps in 2019 I can finally sort that out :fingers_crossed:

Thanks Rich. I did have an oil weep from the gasket but that was fixed by MM a couple of months ago so there's no obvious leak in the engine bay or oil on the gravel etc. I've monitored the oil pressure relative to the temp and it sits at 1.25 bar at 70 then drops to 0.5 when reaches 80 and beyond. I doubt it's the bearing as that would be fairly obvious but could be worn lobes or a pressure relief system problem as Dave pointed out Anyway got it booked back in at MM next month for them to have a check over.

The coupe's in at MM next week to check the oil pressure situation. But in order to brace myself for a biggish bill - how common is oil pump failure? I've had a search through the forum and there's not a lot there so I assume it's quite rare? I also assume that the pump either works or not as opposed to a gradual failure over time? I'm doubtful it's a serious mechanical issue and pinning my hopes on a sensor problem.

Another thing you could consider is to send off a sample of the oil for analysis, amongst other things the measure of viscosity at 100°C can be used to estimate the amount of fuel dilution (if any), and it is then useful to know what is the oil currently in there. Millers Oils offer this service, others are available...

I've known gear failure with a 16v pump but that was instant failure not a drop in pressure over a long period so first rule is to have the pressure read on a mechanical tester, as you say hopefully it's a sensor issue.

Drop in oil pressure on 16 valve engines can also be caused by wear in the balancer shafts' centre plain bearings: A symptom of which is worn cam lobes due to lack of lubrication of the top end.
But before panicking do as Joe says and get a mechanical gauge on it. Access,via one of the sensor points by the oil filter is easily accessible on 16 valve engines.
Fiat specs say that over 0.8 bar at idle with oil temperature of 100ºC is acceptable for a 16V normally aspirated engine.

Cheers peeps - I'll report back with the results