Oil pressure and Oil viscosity
 

On my sbf 302 the oil pressure on 850 rpm idling is 60 lbs. Driving on 2000 rpm it shows 70 lbs.
Oil Temperatur 180°F. No oil cooler.
Oil brand: Castrol Edge 10-60.

Has the higher oil viscosity influence to the idle oil presure?
Would it be better to change at a lower viscosity like Castrol Edge 5-40?

Winter temperatures in my area are approx 45°F. Sommer temperatures up to 100°F.

Suggestions welcome!

Rico

I would not run 10W 60. U will get better FLOW with a lower viscosity oil.

Mark

Wait a minute......a multi garde oil ....10w60....is a SAE.10.oil with additives to make it lubricate like a SAE 60.When the additives break down you're left with a 10 weight oil. Very thin, 5 weight is like water. In our old engines I prefer 20w50. This is why with multigrades oil changes are essential.

Cobra53,

I, too, have a sbf, a 302 stroked to 347. The engine builder recommended 15W-50, 20W-50, or 15W-40. I don't track the car, other than for an occasional autocross, so I use Chevron Delo 15W-40 year-round. (I live in Hawaii).

At idle (850 rpm) with a warm engine (oil at least 180 deg F), the gauge shows 40 psi. On the road at 2000 rpm, it makes 50 psi. At cold start, it makes 60 psi.

These measurements seem "normal" to me. I think you could safely lower your motor oil viscosity to a xW-40 or xW-50, take some new readings, and adjust from there if necessary.

Cheers!

I'll keep it simple, use 10W30 and forget everything else.

Frank

The first number is the cold starting viscosity--the second is the viscosity HOT! Your Hot idle pressure is high. Some of it is due to the bearing clearances and the other is the 60W. You might loose maybe 10lbs at most by going to a 10w40 which would be a good move.
I use a 10w40 for the most part. I have been told my a reliable person that the slightly heaver oil ( as appose to the real light oil crowd at 20W) does a better job stabilizing the hydraulic lifter at high rpms without loosing the effect of oil cooling, by flowing through the bearings clearances. (part of this answer is from my own experiences)
Lou

I have a 347 stroker (ready a 354, but the same) hyd roller with stock volume oil pump. Cold 60 psi and hot idle 45, 2000 rpms it's 50 psi.

10w-30


Dwight

Rico...read Chanmadd's post again and then I would suggest that you do the toughest thing there is for a Cobra owner to do: LITFA (Leave it the f___ alone).

Most cobra owners change oil once, or twice a season (1500 to 3000 miles) and never see 230 Degrees oil temp. Do u really think he is running his engine hard enough to create enough heat to break down his oil to 10w in this time period??????? Not even close.

Oil viscosity is based primarily on bearing clearance not because u have an "old engine" I would bet the farm he does not have a loose bearing package.

Cobra 53
Do yourself a favor and call a couple of lubricant specialist (Joe Gibbs racing, Brad Penn). Then report back on what they say. ;)

Oil
 

I have a 418W with 530 hp with a high volume oil pump.

I run 10-40w. My cold pressure is 65-70. Idle pressure when hot is never below 45. At any higher RPM its 65.
The engine builder initally recommended 20-50W.
I explained my climate in Wis. and they then said 10-40W would be good.

The Nut :MECOOL:

Pressure vs Flow
 

The oil pressure reaches a maximum and never goes higher no matter how high the engine revs. This is because the oil pressure has lifted the pressure relief valve (PRV) in the oil pump. The PRV allows oil to flow back to the pump inlet or back to the pan depending on design, but the point is, the oil flowing out the PRV is not flowing through the engine. Once the PRV lifts, oil flowing through the engine (to the bearings) never increases.

The rpm, at which the oil pressure reaches it maximum, is the rpm where the volume of oil flowing through the engine reaches its maximum. So if the oil pressure hits a maximum of 65 psi at 2000 rpm the amount of oil flowing through the engine has reaches its maximum. You can rev the engine all you want and the flow will not increase. This means that at 8000 rpm the oil in the bearings will see 4 times as many revolutions as it did at 2000 rpm.

Now if you put a thinner oil in, and the engine hits its maximum oil pressure at 3000 rpm, instead of 2000 rpm, then there is 50% more oil volume flowing through the engine, at high rpm.

Oil thins by the shear action in the bearing (basically the speed difference of the inner and outer surfaces). The oil also heats up from this shear action. The longer the oil spends in the bearing the hotter and thinner it gets. It is quite possible to put a thicker oil in an engine and end up with thinner oil in the bearing at maximum rpm, because the lower flow of oil is allowing the oil to stay in the bearing too long.

It is my opinion that more engines have failed because the oil viscosity was too high than failed because the oil viscosity was too low. That said 60 wt oils is a waste of energy pumping oil through a PRV, at best. It may even cause a bearing failure, if the oil flow volume drops too low.

For street driving, I'd suggest a good quality 10W40 and leave it at that. Synthetic or non synthetic is your choice. 20W50 if you are in a hotter climate while driving your car would not be out of the question.


Bill S.

Very well put olddog.

Mmmm. Tribology Porn.

Thanks for all the replys.

Finaly ordered " Castrol Magnatec 10-40 ".

Interessant article about " Multi-Viscosity Lubricants " on the link.

AutoMotiveu.com

Note:
I made my order on a shop in Germany ( this morning). The oil willbe here mid next week. Reason for order in Germany is the price difference . Price in Spain for 10lt is 96€. In Germany for 20 lt inkl. delevery with DHL to Spain 110.50€ !!!!!!!

This morning I took the oil pan off the engine.
No metal bits nor roller bearing needles found.
The oil pump can be easily turned and it looks ok.
Drive shaft (hardened) looks well.
Pump type M68HV (71?) (C3?)
How can I find out, if it is a standard or high pressure pump?

It's a high volume (HV), not high pressure.

HP= High Prersssure
HV= High Volume

Any pump can be made higher pressure, but only at a higher engine speed, by changing the relief spring.

A HP or HV regulated pressure can be set lower or higher for the MAXIMUM pressure.
The HV pump WILL deliver more pressure to the engine progressively up to the regulated pressure because of the larger gear set.
A high volume pump takes more power to turn, so wears distributor and cam gears faster.

10psi per 1000 rpm is still a good rule.

OIl flow though the bearings is more important than oil pressure.

A tight clearance engine with a HV pump and thick oil is a bad example.