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Oil Viscosity Vs. Oil Pressure
Posted 08 September 2008 - 03:13 PM
So, a thinner oil from cold, say a 5W vs 10w will circulate better as it is thinner, but give a lower oil pressure reading right?
My point of asking is that at a recent trackday my Mi oil pressure dropped off a little as it got hot, so by my understanding i need to go to higher viscosity oil to avoid getting the oil too thin and starving a bearing of oil.
Ive been using semi-synth 10w40 since i built the engine, which gives an excellent oil pressure from cold, but when hot it drops quite a bit, now im judging this off the factory gauge and im well aware of how crap they are.
So, my question is such, i do a lot of trackdays where the oil temp gets up, ive got a 13 row cooler which keeps it in check, and even half a lap of cool-down will see it back to normal, so would i be better off with say a 10w50 oil? When the oil is up to temp after a session at 2.5k-3k its somewhere around between the 2nd/3rd mark which i estimate to be between 20-30psi, which seems low to me.
Normal driving (say 3k-ish) is well over halfway, and approaching 3/4 if the car is revving (5k + ), cold start is a full gauge.
Posted 08 September 2008 - 09:12 PM
Posted 09 September 2008 - 07:47 AM
Am i right in saying a 10-50 will be thicker when hot when compared to a 10-40?
Posted 09 September 2008 - 02:16 PM
I didn't think this was anything to worry about and quite normal....
10w/40 semi here too. The haynes actually states 15w/40 as the correct oil last time I looked.
Posted 09 September 2008 - 07:28 PM
Posted 10 September 2008 - 09:48 PM
Posted 10 September 2008 - 09:56 PM
as for the oil pressure it will be low at only 2.5 to 3k, should be 5 or 6 bar at 4k RPM hot or cold IIRC.
Posted 11 September 2008 - 03:16 PM
Posted 11 September 2008 - 04:22 PM
ive always been told that as long as the oil pressure light isnt on then everything is ok, due to the standard guages being pretty crap. i have 5-30 in my 8v and at the last trackday in hot weather the light was just and just flickering after a heavy session!
That's too thin IMO and not the right oil, its designed for new/modern engines with tighter tolerances and probably explains the oil light on hot idle.
Posted 12 September 2008 - 07:25 AM
Depending how anal you are you don't want to see over 110deg although it's "safe" to get to 120-125 I killed my old nova engine from spiking the oil temp.
Would look at the oil cooler set up closely and consider re-siting the cooler or goign bigger again, then carry some cardboard round to cover it for road use, or ducktape then you can tune in the temp on the first session on track.
From speaking to some german VLN race teams they said they aimed at coolant fo 75 and oil of 85deg for max power if youw ant something to aim at.
Posted 12 September 2008 - 08:04 AM
I think its just crap oil if im honest, so i intend to dump it out and thought it'd be worthwhile to try something else.
A lot of people have suggested Silkoline 10w50 fully synth, which sounds just the job, but at £44 for 5 litres its a bloody expensive oil change given the oil capacity of my car with the sump/cooler is now approaching 7litres...