JCScooby

Just fitted an oil pressure gauge (mechanical) yesterday and as i've never had one before i didnt know what reading i should get so im wondering if u guys know what pressure to expect?

so far its been:

Idle (once warmed up)- 25 psi
Cruising at 70mph - 60/70 psi
Booting it through the gears - 90 psi

This sound about right?

[Davey]

Sounds good!

ex-webby

6bar giving it some sounds fine to me.

Regards,
Shaun.

viperkick

dos this sound right

7 bar when i first turn it on cold

3 bar at idle < warm

dont no wot read when im giving it some

wot psi is 1 bar

white

IIRC, 1 bar is around 15psi

Granby

iTrader: (5)

The same as mine

viperkick

nice one

andy97

iTrader: (1)

Using a better quality of oil will help with oil pressure. My car has had a new engine fitted, when on the running in oil, the idle pressure(warm) was 35- 40 psi. The car is now run in and with motul 15-50 oil, idle is 50psi and remains constant, but the running in oil dropped pressure when over 85c

Andy

The Rig

iTrader: (13)

well,heres mine, my95 import.

cold, 6 bar/88 psi

idle, 2 bar/30 psi

booting it, not really looking but sure it goes back to about 6 bar/88psi

Thats using 10w 40 magnatec

monkeyboy173

iTrader: (12)

Fitted my defi BF's over the weekend ive found my oil pressure readings as follows;

Cold switch on 6.8bar
idle when warm 2.8bar
6500rpm 3rd gear 7.8bar

Does this sound to high?

Ive got a bugeye STi and I change the oil every 2000miles with castrol fully synthetic 10w60. Im assuming that high oil pressure is better than low pressure but can it do any damage?

Sorry for the post hijack!

charlesk

V6 TypeR:

7 bar cold idle
2.7-2.8 bar warm idle
6bar cruising
6.7-6.8 bar when booting it

Oil pressure is dependent also on oil. Thicker oils (ie 10w60) will have higher warm pressure than a thinner oil (10w40). As long as the readings stay were the car operates normally, I wouldn't worry about them...

Trap2Terrorist

iTrader: (3)

6.6bar on start up and stays around this most of the time, moving by only a few points of a bar under different driving conditions.

Shark Man

Don't forget high oil pressure doesn't always mean it's getting to the bearings...at high revs most of it will be dumped out your pressure relief valve instead of going to where it should

10w-60 users take note.

monkeyboy173

iTrader: (12)

Sharkman - Don't forget high oil pressure doesn't always mean it's getting to the bearings...at high revs most of it will be dumped out your pressure relief valve instead of going to where it should

10w-60 users take note


Do you think that 10w60 is to thick for the car then? I was under the impression that a 60grade oil would be good for the bearings? Youve got me worried now

Can anybody else shead any light on this??

Shark Man

Right, I've cut and pasted vairous bits I've typed before...so now I'll run off before the **** bunch can catch up .....

Right then, the primary answer is a question: It Depends on use.

If your not going round race tracks, or rallys. Running 350+bhp, or thrashing the living nuts off it day in day out. Then I'd say your wasting your money.

For starters, the thickest oil Subaru state for a pre2000 uk classic under "harsh conditions" (e.g towing, high ambient temps, tharshing it and running higher than stock BHP) is 15w-50, or 20w50 (10w-50 and 5w-50 is not listed but it also fits in that band). 10w-60 is not listed or recommended anywhere.

Secondly the bearing/journal clearances are of a tight enough tolerance to allow for thin oils to maintain a boundry layer without them being sqeezed out the sides. The thicker is better slogan is an outdated statement given when engines were built to sloppy tolerances and had larger bearing clearances.

The exception is, if your engine is worn causing lost oil pressure through leakage out the sides of excessive bearing/journal clearances (cue a big end failure sooner or later ).


Thirdly, pump cavitation and air bubble retention in thicker oils - that's a long winded debate on its own there.

Fouthly. Cold/warm viscosity. A 10w60, at 40degrees (still too cold) flows like a monograde 50 oil at the same temperature (an oil grade from the 1940's used in vinatge stuff). As the molecule chains start expanding too soon. Even though it says 10w-60, at above zero degrees its flowing worse than a 20w50 oil (oil grade from the 1970's). Not good for cold starts, warming up, short use, or doddering round town.

Finally, Pressure vs flow. High pressure doesn't mean high flow. Flow of oil is needed for cooling the bearings and to replace and maintain the boundry layer between the journals and bearings which is lost when it is squeezed out under load.

The engine oil pump has a capacity of flowing gallons of oil per minute with a open end resulting in near zero pressure. Restrict its flow by feeding it to bearings and oil galleries, which are about 1/4" in diameter. You are not going to get gallons a minute, but what you'll see on the guage is a high pressure. Use a thicker oil, flow goes down futher, but pressure rises as the oil drags more and is more difficult to pump through the barrow oil galleries.

Add to that the oil pressure relief valve. That is there to to maintain a more constant oil pressure across the rev-range. If the oil is thicker it will open more, and at lower revs, not a problem. The higher the pressure the more it will open. So whats the deal? Well in aid to reduce the high pressure your losing more oil flow out the relief valve rather than going to the bearings and aid cooling. Your not going to starve the engine of oil, as oil is present in the bearings and galleries, it's just not flowing out as much...so it has to go somewhere - out the relief valve. Therefore - High pressure, Low flow.

So, what is important about oil flow? Well converse to most peoples thinking, your engine is primarily OIL COOLED. Not water cooled - the only parts that is water cooled are the cylinder heads, inlet manifold, turbo bearing housing and upper section of the cylinder block. Bearings (including turbo), cams crank, underside of pistons etc are all OIL cooled. The more flow, the better cooled these can be.

The final factor in oil cooling, is thinner oils cool better as they have a better specific heat capacity. The interesting thing here, is that when using a thinner oil. You will actually see higher sump temperatures, as it flows more and gains heat quicker. Problem is, being thin already, it will thin out more. If under hard use/high BHP, it can get too thin if the oil cooling system cannot cope (stock water to oil cooler)- thus the need thicker oil for hard use.

Gerenally speaking, the point at which this starts to becoming critical with a 5w-40 10w-40 oil is above 110-120degrees C. This will be noted by a drop in oil pressure. If excessive it will reach the point it is below manufacturers minimum limits. Switching ONE GRADE thicker should resolve and still be within the manufacturer's oil reccomendations. Unless the car is excessivly modified and/or raced/tracked/rallied.

This is why for a pre year 2000 UK cars, Subaru reccomend 10w-50, 15w-50 or 20w50 for harsh conditions instead of the 10w-40 used for "normal driving conditions". Later model year cars use even thinner oil grades.

monkeyboy173

iTrader: (12)

WOW what a response!

So in short i should change my oil

I do it every 2k miles anyway and im only about 100 miles short so not the end of the world.

Millers or silkolene(spelling?) any recomendation

Thanks for your help

This place is great I havent not been able to find one single query ive had yet top work

Cheers

The Rig

iTrader: (13)

just rechecked mine, on crusing at about 70 mph im at about 5 bar.