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[Kevin Wood]

Granted if it's only flickering at idle it's probably not doing too much damage - as long as the pressure is healthy off idle. But what cars come fitted with oil pressure gauges these days? 

No many, more's the pity. Mrs. KW's MX-5 has one, but it's fake and just fed from an oil pressure switch.

I know the majority of drivers wouldn't have the first clue what it's telling them, but for those who do it can mean the difference between a wrecked engine and a lucky escape.

[aaronjb]

Granted if it's only flickering at idle it's probably not doing too much damage - as long as the pressure is healthy off idle. But what cars come fitted with oil pressure gauges these days? 

No many, more's the pity. Mrs. KW's MX-5 has one, but it's fake and just fed from an oil pressure switch.

I know the majority of drivers wouldn't have the first clue what it's telling them, but for those who do it can mean the difference between a wrecked engine and a lucky escape.

Indeed! The 300ZX has one, but that's the last (production) car I saw with one in  :-/ Better to save a few quid on every car and pay out the occasional warranty claim than spend the extra on every single car, I suppose.

The number of times I've seen "I was doing 70 on the motorway and the light came on, now the engine sounds like a bag of spanners.." just isn't funny (especially on the MR2 which has somewhat of a reputation for drinking the contents of it's own sump)

[Kevin Wood]

The problem is, if you give an idiot a gauge they will constantly worry about it, and oil pressure does vary significantly within acceptable limits, as we know.

There would be those who would pester their main dealer every time it varied.

Same with temperature gauges, and why a lot of cars are going to warning lights there. People see it vary and worry.

Again, the MX 5 example. The temperature gauge is fed by the ECU and it rises steadily to the mid position after startup and stays there despite the actual temperature varying. I know that for a fact having forgotten to reconnect the cooling fan after the last cam belt change. Sat there wondering why the coolant temperature was stable but the fan hadn't kicked in. All of a sudden "Boing!" up into the red about 5 seconds before the pressure cap let go and all hell broke loose.

So, cars are made "idiot proof". I do wonder why they don't build a bit of intelligence into the "red light", though.

i.e. 1.5 bar of pressure at idle= OK,

1.5 bar with WOT passing through 5000 RPM =

Then again, I'm sure selling replacement engines is a lucrative business for them.

[aaronjb]

Very good point - I suppose that's why they're called "idiot lights"; any idiot can tell when something is wrong by looking at them..

Cheap senders used on gauges tend to fail over time as well and I suspect (though this is just a guess really) that a simple pressure switch is more reliable - older 300ZX's often have 'vagueometer' senders for oil pressure & coolant temperature.

I suppose that's why they don't have a variable trigger point warning lamp for oil pressure, too. Actually I wonder if any aftermarket dash has that feature (I'm thinking of things like the Stack digital dashboards)?

You're right though - much more profit in replacement parts than cars, I imagine!

[Kevin Wood]

Yep, fair point. Oil pressure transducers are pretty unreliable unless some decent money has been spent on them.

Variable oil pressure warning sounds like a new Megasquirt feature unless it's already been done.

TBH most who care probably install a 2BAR+ pressure switch and accept the fact that it'll flicker when they sit idling in traffic on a hot day.

[Andy B]

Autodata suggests that oil pressure should be 2.0-2.5 bar at 750-950 rpm

HTH

Correct!
Just been to MB to get another oil filter and asked him what pressure the pressure switch put the light on. He didn't know :-? but  dug out the pressures at cold idle & hot idle. Cold it should be 4.0 to 4.5 bar and as you say 20 to 2.5 bar at operating temp.

What he also went to to say was, that they do a 're-build kit' of parts ie shell bearings, gaskets, head bolts, timing chain & sprockets etc etc. All told comes to £333.72 inc vat which, considering MB prices doesn't seem too bad.

[aaronjb]

Yep, fair point. Oil pressure transducers are pretty unreliable unless some decent money has been spent on them.

Yup, I chuckle each time folks on the Cobra forums post about their hideously inaccurate - and very expensive! - period-look electric sender gauges.. They require a special external 10.5V voltage regulator, and even then seem about as accurate as a Channel 5 weather forecaster.

Variable oil pressure warning sounds like a new Megasquirt feature unless it's already been done.

That would be quite interesting I was pondering the idea of throwing out the Accel DFI & Ignition system on the FE and going Megasquirt.. then again, the Accel stuff does look quite nice (and it's not cheap new!) - the 'distributor' (really just a position sensor in a fancy billet housing) looks very nice indeed.

[Kevin Wood]

I was pondering the idea of throwing out the Accel DFI & Ignition system on the FE and going Megasquirt.. then again, the Accel stuff does look quite nice (and it's not cheap new!) - the 'distributor' (really just a position sensor in a fancy billet housing) looks very nice indeed.

It's not exactly rocket science (despite what some would claim) so, if you have a complete set of bits including software to tune it, etc. why change it? (unless you can sell it for silly money).

[aaronjb]

It's not exactly rocket science (despite what some would claim) so, if you have a complete set of bits including software to tune it, etc. why change it? (unless you can sell it for silly money).

Largely just because I like tinkering - and Megasquirt gives endless opportunities for tinkering Though as you say, probably not worth complicating matters, really.

[Marks DTM Calib]

To be honest, running with oil pressures that low on modern cars even at idle, is not going to lube the bearings that well particularly as modern engine are more reliant on pressure than flow.

[Andy B]

... as modern engine are more reliant on pressure than flow.

ie to support the big end or main bearing with pressurised oil rather than white metal to crank contact.
It'll give me something to do won't it!  It must be 20 years ago since I've been so far inside an engine .......  :-?

[Marks DTM Calib]

... as modern engine are more reliant on pressure than flow.

ie to support the big end or main bearing with pressurised oil rather than white metal to crank contact.
It'll give me something to do won't it!  It must be 20 years ago since I've been so far inside an engine .......  :-?

Go through the above checks first 

[Andy B]

re spec. I've found a trusted Smart engine rebuilder's website recommending 5W-50  :-? :-? so even viscous-er!!

[Kevin Wood]

re spec. I've found a trusted Smart engine rebuilder's website recommending 5W-50  :-? :-? so even viscous-er!!

Hmm. But that's always the bodger's solution to low oil pressure.

Manufacturer's recommended oil should really work. They will have done plenty of testing on it. Someone who can rebuild an engine is not necessarily qualified to specify an oil for it, and an engine where it drops to 0.35 BAR regardless of whether the oil is a grade above or below the recommended has issues, IMHO. :-/

Maybe you'll get 0.45 bar with a thicker oil so the light goes off.  Problem solved except there's now less oil flow.

I would say get it checked with a gauge and check the relief valve for a start.

[Andy B]

...
Maybe you'll get 0.45 bar with a thicker oil so the light goes off.  Problem solved except there's now less oil flow.

I would say get it checked with a gauge and check the relief valve for a start.

At the moment the low oil pressure light seems to be behaving itself with Vx's finest semi-skimmed 10W-40 in! 
There's a cheap gauge on eBay at the moment clicky but I think we all know what it'll say.