…just run in then!
Your oil pressure exactly same as mine - spot on! My mileage not far off that too.
thanks everyone, feel much better about the car,
Sounds about normal to me. Mine will go to 6 when cold but when up to temp it is about 4 @ 3000/3500 rpm an about 2 @ idle.
There is a mountain out a mole hill being created here!
Yes.
The gauge is unlikely to be accurate anyway, and the behaviour is absolutely normal (higher when cold, lower when hot, lower at tickover, higher with more rpm).
To the OP - it’s not high oil pressure you need to worry about, it’s low oil pressure. 60psi is not going to blow the top off the engine. All it does is force oil into the bearings which is what the engine needs. High oil pressure is not like high blood pressure, you don’t need treatment to reduce it 
I now understand why Mazda and other manufacturers dumbed down the gauges, although I am annoyed by having the later gauge that adds nothing to the information provided by the light.
Shame they aren’t separate gauges rather than being built in to the “instrument” cluster. I’d offer to swap my “comfort blanket” version for a proper one
Yep, does anyone have the ordinary owners manual for a 1.8 Mk1 to help out the op here? The correct oil will be shown in there.
No, but I have the Grainger & Shoemark “Enthusiast’s Workshop Manual” for the Mk 1 1.8 (there isn’t one for the Mk 2 as far as I know, more’s the pity).
It states:
API SG, SH, or higher (ECII)
Above minus 25 degrees C, SAE 10W-30
Below 0 degrees C, SAE 5W-30.
Looks a bit odd in print but makes more sense in the diagrammatic form in the manual (it’s exactly the same values as my Mk2 manual as it happens).
Basically, the answer is 10W-30 unless you live in Siberia, northern Canada etc.
Just get the OE one working or fit a aftermarket ones.
M-m
I just threw in some new 10W40 fully synth and the oil pressure gauge is now 90 lb/in from ice cold (rather than pegged past it as it was before the oil change - which was badly overdue because it may as well have been ink in there) and eventually goes down to 30lb/in when idling on warm and 60lb/in when going down the motorway at 70mph, whereas before it would only get down to about 40lb/in at best with whatever oil the previous owner had.
Frankly, the only values that should ever cause concern are never moving down from 90lb/in or higher, where I would change the oil, or no pressure at all, where I’d stop immediately and figure out if my oil has just vanished or the pressure sender has clapped out. 
On a car like this, the gauge is basically a toy and shouldn’t be treated as anything more than a light with a cool extra dial for your dash. With all the worry it must cause I can see why these gauges are now all ‘fake’ dials. I’m ‘more the merrier’ on my dash instruments though and am having to restrain myself from adding more of the bloody things - I got to use a vehicle with an ammeter and a voltmeter for a while and while basically nigh-on useless 98% of the time, I always take a shine to information overload.
Paul 
I suspect the moment has passed for the OP, who posted in September, but the point for posterity to note there seems to be that Paul’s 90psi is exactly the same as the 6 bar that the OP was concerned about, so perhaps not unusual.
I like instruments too, preferably little round gauges to tap, but I admit I have been out for a run today in company with another MX5 and an MG-F of similar vintage, just for the joy of it, and I don’t recall looking at either of my dumbed down gauges
Not in a Mk 1, engine was built to run on sem/part synth.
M-m
Ok but why not throw in some 20W50 and why do Mazda say 30 grade?
Put your favourite oil name plus pdf in the search line of Google and it will bring up the data sheet. I put a few popular oils in a table in order of thickness and it may explain why the guys with 90psi oil at cold have that excess pressure; the oil is thicker when cold than the bypass (60psi) can handle. It won’t be a problem warmed up but I would go easy til then as it must put extra load on the pump and gears and will not flow round the engine so well.
These are the industry comparison temps; 40C is hand warm and 100C is boiling water around fully warmed up, though track cars will run the oil hotter still. It’s a controlled running environment, ambient temp only comes into it when the engine is cold. We can see that even the thinnest oils are massively thicker at lower temp than the thickest ones are when hot, and at their W temp they are of course thicker still. It’s also interesting to see how the “fuel saving” 913C grades are still 30 weight but are chosen from the lower end of the viscosity spec.
Good table.
FWIW, I’ve just ordered 5L. of Millers Trident 5W30 semi-synthetic, at about £18.50 delivered (not the fully synthetic long-life version).
The corresponding figures for your table from the data sheet are 63.9, and 11.2.
I had a bottle of 4L Castrol 10W40 fully synth lying around, and anything is better than that black filthy ■■■■ that the engine was choking on. I know it’s not the ideal/recommended oil for the car and UK weather - this is a flush-out change that I’ll redo later with a more suitable oil. The car’s had a hard life before my ownership, running a slightly heavy synth oil for a thousand miles or so isn’t going to hurt it appreciably.
Tomorrow I am dropping the 5w-30 GTX winter oil and plopping some £4.50 a Litre from Tesco 10w-40 Magnatec in for the summer and Nurburgring, I really dont care what the guage says afterwards as long as it shows some pressure 
Yes that looks a good choice John. In a way it’s more important that our post 94 cars are filled with the book oil as the gauge will always give the “right” figure unless there’s no pressure at all so we have no other way of knowing all is well. The early cars at least have the working gauge so they can see what’s happening.
It would be interesting to hear from any pre 94 Mk1 owners running 5W30 or 10W30 about what their gauges read. Do they also go to 90psi etc? Anyone changed across grades either way and noticed a difference? The numbers on that table clearly mean something but it would be good to see how they translate into real life.
I’m currently on Mobil1 5W30 (getting old now, about 18months and 6k) and easily see full scale when very cold above 2000rpm ish (just under that at idle, maybe 80psi)- 60ish driving normally when warm - and just under 30 at idle fully hot.
I’m just about to flush and change to Castrol GTX 10W30. I’ll let you know what happens.
Jon
Castrol GTX 5W/30 is a stateside brew, Castrol in the UK do not even have a product sheet listed for.it. GTX 5W/30 is available in the UK to the garage trade but not generally available at retail.
eddie
Don’t worry about it. Mines very similar, I just make a point of not giving it some stick while the reading is high. I used to have a Lotus Cortina years back which had high pressure at start up, but I used to live on a fast A road and sometimes had to put my foot down asap. Quite often had oil leak from cam cover when doing this. Of course it could have been the Lotus engine, but I’ve always been wary since then.
iddy
That would be crankcase pressure (blow by) rather than oil pressure, if it came from the cam cover gasket.
A common leak on MX5s I think, if the gasket itself isn’t spot on. Mine was terrible before the head was redone, there was so much oil around I couldn’t even be sure it was that, but it doesn’t do it now so it clearly was!