silent running

Just fitted my oil pressure gauge on the end of an adapter in the oil pressure switch location. Oil is Motul 10w40 synthetic and it's a standard WRX 2.0 lump.

Pressures at 80-90 degrees C:
750 rpm idle = 1.5 bar
1000 rpm = 2 bar
2000 rpm = 4 bar
3000 rpm = 5 bar

Cold idle = 6 bar

It's really only the hot idle that I'm a bit concerned about. Is it just that the oil pump isn't very efficient at very slow speeds? Engine was rebuilt 5000 miles ago and I just changed the oil a few weeks ago. Any comments welcome.

ZEN Performance

A little low for my liking. I generally like to see over 2 bar at idle, and 6 bar max when hot, certainly from 4000rpm. What sort of gauge?

silent running

The SN group buy specials - a set of three, boost, oil temp and oil pressure. TBH they work pretty well and they're stepper motor controlled. The senders and wiring are all very good quality and the readings seem right. Boost for example matches up pretty much exactly with the FC Commander and the same as I used to see on my Autometer boost gauge. Oil temp responds right, i.e. takes about another few minutes after water is up to temp before getting warmed up, then finally sits at a stable 80-90 degrees.

The fact that the other gauges are working fine, and that this one seems to be showing good numbers above 1000 rpm, makes me think it's my oil pump rather than the gauge. I may be wrong, but it seems logical. I'll take it out for a run now and see what it gives me at 4000 and upwards. IIRC, on a WOT run up to 6000rpm it maxed out at 6 bar.

ZEN Performance

I doubt it's the pump. the releive valve should regulate to 6 bar with sufficient oil, but temperature makes a difference, even between 80ºC and 90ºC. Pressure at high RPM is most important, it could just be the engine is pretty loose and the releive valve is a little slack.

I wouldn't say it's a sign of impending doom though.

Paul

P1 FEK

iTrader: (1)

Those figures match mine, always wondered if they were ok. I use 10w40, do wonder if i would get better reading with different oil, maybe 10w60?

GazJenno

I had a crap make 10w40 in mine and was still getting 2.3bar at hot idle and always around 6bar at 4krpm. Changed to motul 15w50 and it now holds 3bar at hot idle and above idle follows the same pattern as when I had the 10w40 in their.

However putting thicker oil in there so your gauge reads higher doesnt mean much I dont think, the flow of oil will still be the same it will just have a higher pressure as its harder to flow.... I think thats right.

Gaz

silent running

Thanks for all the input. Well I've been out for a proper drive with a pad and pencil to note down what's what. I think last time my readings were at roughly 80 degrees, and as you say Paul, it seems that there's a big difference between 80 and 90. Once it had properly warmed through, the oil runs at 85 to 90.

Anyway it still cold idles at 6 bar/90 psi. The hot readings at 85 degrees and above, rather than 80, are:
750 rpm = 20 psi
1000 = 30 psi
2000 = 58 psi
3000 = 70 psi
4000 to 6500 = 70-75psi

Once at the right temperature, it stays pretty much solidly on 70-75 psi the whole time while driving, dropping slightly when going below 3000 rpm. It definitely drops right down to 20 psi when sticking it in neutral and letting it idle. Having a look at the specs on my Subaru workshop manual it quotes for 80 degrees, 15psi+ at idle and 45 psi+ at 3000 rpm, which mine easily achieves.

So I guess I don't need to switch to 15W50 just yet.