Discussion
Podie said:
15psi when warm at idle... when cold, sits about 30.
Overheard an anorak type saying these engines are more critical on volume of oil, rather than pressure...
Quite a few good threads on this topic on the forum but in brief: some of the main factors are:
1) Pre-seprentine or serpentine front-end, the old type gear pump on the pre-serp engines isnt as efficient in terms of flow rates (especially at higher temps) and so tends to give slightly lower hot pressures say 15 (idle) to 40 psi (3000rpm) as a guide. The later pump has a greater capacity and mine will produce 30 to 50 psi with oil at 100-110C. About the volume thing, yes the rover unit's oil system is all about flow rates (volume per second - not volume in the sump)rather than oil pressure per se.
2) Oil if you use Mobil 1 (i do) make sure its the higher viscosity Motorsport version (15-50w) not the ordinary 10-40w gnats piss. Mobil 1 motorsport is an excellent (but expensive) oil.
3) Oil pressure readings on the dash are totally dependent on the calibration of the gauge and the sender unit. The latter of which is notoriously inaccurate. I recently spent some considerable time calibrating mine against an independent calibrated mechanical gauge across a whole range of oil temperatures so i know mine's pretty much spot on (at the moment anyway). If you get odd readings, either way, there is a very good chance that it is the electrics at fault, but one must always assume the worst until proven otherwise!
4) Mr opeoilman has produced some very interesting (esp for anoraks
)and informative threads about the whole lubrication issue, well worth a look if you want to get into the nitty-gritty. Hope thats of some help....
I'll get my anorak......
>> Edited by tahiti450 on Wednesday 1st June 23:11
tahiti450 said:
Quite a few good threads on this topic on the forum but in brief: some of the main factors are:
1) Pre-seprentine or serpentine front-end, the old type gear pump on the pre-serp engines isnt as efficient in terms of flow rates (especially at higher temps)
You mean especially at lower temps, as your following figures confirm:-
tahiti450 said:
and so tends to give slightly lower hot pressures say 15 (idle) to 40 psi (3000rpm) as a guide. The later pump has a greater capacity and mine will produce 30 to 50 psi with oil at 100-110C. About the volume thing, yes the rover unit's oil system is all about flow rates (volume per second - not volume in the sump)rather than oil pressure per se.
2) Oil if you use Mobil 1 (i do) make sure its the higher viscosity Motorsport version (15-50w) not the ordinary 10-40w gnats piss.
The ordinary stuff is 0-40! 10w-40 (not the other way round, the w is for winter) is thin but not too bad:-
opieoilman said:
Viscosity at 40degC........Viscosity at 100degC
15w-40.......110cst.............14cst
10w-40.......100cst.............14cst
5w-40.........90cst............ 14cst
0w-40.........80cst............ 14cst
At lower temps as long as you have oil pressure flow is more important to engine wear than anything else!
Hence if you need an sae 40, 5w-40 is better than 15w-40 all round as it affords the same hot protection but gets round the engine quicker when cold as it's not so thick.
tahiti450 said:
4) Mr opeoilman has produced some very interesting (esp for anoraks
Yep.
opieoilman said:
There are some very important things to bear in mind here and they are as follows.
Unless you are getting high oil consumption or low oil pressure there are no benefits to using a 10w-60 because...........Thinner is in fact better.
Thinner oils dissapate heat better.
There is less oil drag and therefore in most cases this translates to marginally higher BHP at the wheels.
Thicker oils are more likely to cause cavitation.
Thicker oils are slower to release air.
Thinner oils give better fuel consumption returns.
So you see it's not a case of "can I use it" but more a case of are there any benefits?
If you are worried about an sae 40 or 50 being "too thin" then look at the oil temperatures you are running and bear in mind that a an average 5w-40 is in fact thicker at 110degC (12.00cst) than a 15w-50 is at 140degC (8.00cst).
You could be dragging a heavier oil round your engine than is needed and there are no benefits to this.
The next most important thing is shear stability.
An oils viscosity will decrease as the engine temperature rises. Viscosity Index Improvers are added to reduce this thinning. They are a key addative in the production of multigrade oils.
VI Improvers are heat sensitive long chain, high molecular weight polymers that increase the relative viscosity of the oil at high temperatures. They work like springs, coiled at low temperatures and uncoiling at high temperatures. This makes the molecules larger (at high temps) which increases internal resistance within the thinning oil. They in effect "fight back" against the viscosity loss in the oil.
"Shearing"
The long chain molecules in VI Improvers are prone to "shearing" with use which reduces their ability to prevent the oil from losing viscosity. This "shearing" occurs when shear stress ruptures the long chain molecules and converts them to shorter, lower weight molecules. The shorter, lower weight molecules offer less resistance to flow and their ability to maintain viscosity is reduced.
This shearing not only reduces the viscosity of the oil but can cause piston ring sticking (due to deposits), increased oil consumption and increased engine wear.
Like basestock quality, VI Improvers also vary in quality. The best quality ones are normally found in synthetic oils (Group IV - PAO / Group V - Esters) and it is important to understand that the less of these in the oil the better the oil will stay in grade.
Which oils require more VI Improvers?
There are two scenarios where large amounts of these polymers are required as a rule.
Firstly in "wide viscosity" multigrades. By this I mean that the difference between the lower "W" number and the higher number is large for example 5w-50 (diff 45) and 10w-60 (diff 50) are what is termed as "wide viscosity" oils.
Narrow viscosity oils like 0w-30 (diff 30) or 5w-40 (diff 35) require far less VI Improvers and therefore are less prone to "shearing".
Secondly, mineral and hydrocracked (petroleum synthetic oils) require more VI Improvers than proper PAO/Ester (Group IV or V) synthetic oils as they are less thermally stable to begin with and this is due to the non-uniform molecules in petroleum oils as opposed to the uniformity of synthetics built in laboratories by chemists.
It is a fact that some synthetics require little or no VI Improvers to work as a multigrade due to their superior thermal stability.
How to identify a good "shear stable" oil.
API and ACEA both conduct tests called HTHS (High Temperature/ High Shear) and all oils carrying these specifications are tested and scored.
For all oils, these test results are available however, they are often ommitted from the oils technical data sheet! Oil Companies have a tendency to publish the figures that they want you to see and therefore you often need to dig further or ask for certain information when comparing the performance of various oils.
High-Temperature/High-Shear
This test is a simulation of the shearing effects that would occur within an engine. In fact, it's actually designed to simulate motor oil viscosity in operating crankshaft bearings.
Under high stress conditions where shearing can occur, the VI Improvers (polymers) break down. As they do, the viscosity of the oil decreases. This is what the High Temperature/High Shear test checks for.
The HT/HS test is measured in Centipoise (cP) as the Cold Crank Simulator test is. However, in this case, because you're hoping for the least loss of viscosity with an increase in heat and stress, you want the cP value to remain high.
Each SAE multi-viscosity grade has a specific lower limit for the HT/HS cP value. If a multi-viscosity oil cannot achieve a cP value above that limit, it cannot be classified under that viscosity grade. For instance, according to the SAE specifications, an oil must achieve an HT/HS cP value of 3.7 or higher in order to be classified at the 15w40 viscosity grade.
The thinner the oil the lower the number.
Comparisons of HTHS numbers.
Here for comparison sake are a few numbers that we have compiled from data sheets and requests to the oil companies concerned. These are well known oils and considered to be "quality" synthetics so these comparisons are relevant.
Silkolene PRO S 5w-40
HTHS 4.07
Motul 300V 5w-40
HTHS 4.51
Silkolene PRO S 10w-50
HTHS 5.11
Motul 300V 10w-40
HTHS 4.19
Silkolene PRO R 15w-50
HTHS 5.23
Motul 300V 15w-50
HTHS 5.33
Mobil 1 Motorsport 15w-50
HTHS 5.11
Castrol RS 10w-60
HTHS 3.70
Cheers
Simon
tahiti450 said:
1) Pre-seprentine or serpentine front-end, the old type gear pump on the pre-serp engines isnt as efficient in terms of flow rates (especially at higher temps)
19560 said:
You mean especially at lower temps, as your following figures confirm:-
tahiti450 said:
and so tends to give slightly lower hot pressures say 15 (idle) to 40 psi (3000rpm) as a guide. The later pump has a greater capacity and mine will produce 30 to 50 psi with oil at 100-110C. About the volume thing, yes the rover unit's oil system is all about flow rates (volume per second - not volume in the sump)rather than oil pressure per se.
2) Oil if you use Mobil 1 (i do) make sure its the higher viscosity Motorsport version (15-50w) not the ordinary 10-40w gnats piss.
no, I meant the early pump's capacity to pump hot-thin oil is inferior to that of the new pump. When the oil is cool and thicker (so escapes past / through clearances more slowly, such as in the pump and at bearing surfaces) it is much easier to build up pressure since the flow rate will be lower, with much of the output passing through the relief valve at higher revs, hence the plataeu at max oil presure. So the difference in system pressure with cold / cool oil is less pronounced between the two pumps, becoming more noticeable at higher temps when the new pumps higher flow capacity mainatins pressure better.
19560 said:
The ordinary stuff is 0-40! 10w-40 (not the other way round, the w is for winter) is thin but not too bad:-
you're quite right - it was late, .. apologies. >> Edited by tahiti450 on Thursday 2nd June 18:31
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