Hi there, wondering if anyone can help me. Having just bought a 1992 Roadster, the oil pressure gauge is reading high, circa 5 - 6 when driving at normal speeds and acceleration and between 2 - 3 when idling. My current Roadster reads nowhere near that high, even the engine is on its last legs!!!
Can anyone give me any hints as to what could be causing it? Is it something to worry about? I will be doing all the usual changing of oil, filters etc this weekend, but in the meantime some tips would be gratefully received!!!
Sounds normal to me. Oil pressure should be high at idle when cold, then drop to 2-3 when hot at idle, and should increase with engine speed. What you don’t want is high oil pressure at idle on a hot engine; its probably a faulty sender unit, but may be a stuck relief valve.
5 - 6 would be normal while the oil’s still cold, but high if it’s warmed through. Probably nothing to worry about, though. Do you happen to know what oil’s in there at the moment?
Thanks for replies. Unfortunately no idea what oil is in her at the moment, but will change at weekend. In terms of the relief valve sticking is that something I can check myself, or should I ask someone who knows what they are doing to look at it?!!!
The pressure relief valve is between the oil pump and the pressure sensor, and allows some oil to escape back into the sump if the pressure is too high (as it might well be when the oil’s cold and thick). It’s not something you can get to without opening up the engine, but if it were a problem the first line of attack would probably be to flush the engine and see if that clears it…
I suspect (though I’ve not experienced it) that a stuck-closed pressure relief valve would have the symptom of over pressure ( >6 kg/cm²) when started from cold.
Hi Tim - before changing my oil (no idea waht was in it before as I have only had it a month) my pressure was reading 3-4 at idle (cold) and then 2-3 when warm. I flushed and replaced oil and filter (Mobil 3000F1 5w 30 as recommended) and now it sits at 5-6 cold, dropping once warm. Don’t think its anything to worry about though given the other comments. There’s so many oppinions on what oil to put in when you search the forums depending on age / mileage / time of year etc and I went with the Mazda recommendation in the end - see how it goes, may need to go for a thicker one. Does anyone know, when does the release valve kick in?
Do not forget the sender unit or the gauge could always be defective. One point though is the oil grade. A lot of people talk of the 5w30 but to be honest in an old car that sounds a bit low for me, unless you are going to change grade in the summer. Looking at the above chart I would pick a 10W40 or 5W40 as hopefully you will get some time above 0 deg C.
I find mine runs when cold with a pressure of 3 to 4 at idle when cold and it falls to @ 1.5 when fully warm. At higher revs it is @ 5 to 6 when cold falling to @ 4 when hot. (I tend to limitt revs when cold to respect its age so not found the maximum it will go to)
