Oil, some interesting figures!

[oilman]

Ok, before anyone flames me or tells me the following is not relevant, I'm posting this as it was in answer to a question I had concerning oil temperatures and viscosities.

 

As you chaps love information and a debate I thought this worthy of posting!

 

My question to the boffins was:

 

When is an engine up to temperature?

 

The answer was as follows:

 

It is better to turn this around and ask: At what (sump) temperature is an oil at a viscosity that suits a modern high-RPM engine?

 

Present day designs seem ‘happy’ on an oil viscosity of 10 to 15 cSt. (But many are OK on less than 10.) 30cSt is too high at high RPM. It can lead to foaming, air entrainment and cavitation.

 

.......Temp. for 30cSt (Deg. C)......Temp. for 15cSt.......Temp. for 10cSt

 

5W/40 grade.....71...........................90........................117

10W/40 grade....70..........................99.........................118

10W/50 grade....80..........................109........................130

10W/60 grade....89..........................119........................142

 

This shows that a 5W/40 or a 10W/40 is perfectly adequate for all engines except those that run an unusually high temperature.

 

Also, a thick oil can lead to trouble unless properly warmed up before high RPM is used.

 

I found this reply a different but more interesting take on the old viscosity question. I hope you do too!

 

I guess the debate starts here ;)

 

Cheers

Simon

 

sales@opieoils.co.uk

[Mick Day]

Oh dear the gates of Hades open yet again!...........It's mighty interesting though 😬

[Tony C]

First question: My oil temp sensor is in the return line from the dry sump pump to the tank, so is not registering actual sump temp - I guess a little lower.

 

Winter driving on the road with 'proper' synthetic 5W/40 gives 75 deg C and today was showing 85 deg C - so how can I increase the oil temp?

 

In front of the engine tank on my K-Series is already lagged.

 

BRG Brooklands SV 😬 It seems that perfection is achieved not when there is nothing more to add, but when there is nothing more to take away. (Antoine de Saint-Exupery)

[Mr Locust]

Tony,

 

the correct place to monitor the oil temperature is in the oil rail of the engine i.e. in the condition where it has passed through any pumps, coolers etc - what the bearings see.

 

Ian

 

Green and Silver Roadsport 😬

[shn7]

Well this didn't generate much debate. Does this mean all the argumentative types were'nt members or are you all just keeping quiet .

 

Steve.

[Pierre Gillet]

My engine runs with Motul 300V 5W40 and a Laminova and it almost never get to 90 °C on the road.

Seems that it is a bit low for high RPM ☹️

 

 

Pierre

 

Edited by - Pierre Gillet on 23 Jun 2005 07:47:15

[Alex Wong1697456877]

What a conundrum. My engine runs at 80deg oil on the road and 110 + on track. I have seen 115 degC. I use Mobil 1 15/50.

 

From the chart, the oil isn't likely to be getting thin enough till it's over 109degC. Sounds like a 5/40 might be a better compromise for me.

 

Next question is at what temperature is oil too hot - either for itself or for the engine?

 

Alex

 

 

Edited by - Alex Wong on 23 Jun 2005 08:50:05

[shn7]

But then where are we all measuring the oil temp and where do the figures oilman quotes get measured?

 

Steve.

[frankyknuckles]

The Stack readings on my dry sumped R300 are as follows.

 

For road driving, I do not think I have ever seen 90 degrees, but have a very stable 60 to 65 psi, on average temperature days, the oil temp seems to be 69 to 75 degrees, on very hot days like we have had recently, the oil temp might creep towards 85 degrees.

 

I can't remember what temps I get on track but will check next time.

 

These temps are taken from the bottom of the bell housing, how does the temp reading here compare the oil temp in the oil rail?

 

I am using the recommended oil from oilman, Silkolene Pro S 5w/40.

 

If I'm reading the numbers correctly, it seems the oil never gets thin enough on the road ?

 

www.R300.net

[Dirty Den]

I assume those figures are for a normal "wet" sump car Oilman? So presumably a car with a dry sump will take longer to warm up?

 

I don't think I've ever seen my oil temperature go higher than ~75c on the road and ~85c on the track. Car is a dry sumped 1.6 Supersport run on Mobil 1 0w/40.

 

Den

 

http://www.dens7.co.uk

[oilman]

The oil temperatures are measured as the bulk oil temperature.

 

In answer to a lot of comments so far.

 

The main conclusion of what the boffins are saying is that many people use thick oils unecessarily by that they mean sae 50's and 60's when a lower viscosity oil would better benefit the engine from a wear and BHP at the wheels perspective due to better flow and lower drag.

 

What most people forget is that thinner oils dissapate heat better.

 

So long as reasonable oil pressure can be maintained, thinner oils have more benefits than downsides however many enthusiasts get hung up with the misconception that thicker oil is better. As you can see, this really only applies in extreme cases.

 

As was recommended by me some time ago, a proper fully synthetic (shear stable) 5w-40 is for the majority of cases the best option for engien longevity and performance.

 

Cheers

Simon

 

sales@opieoils.co.uk

[paul.davis]

I run a wet sump with a water temp sender (taper) screwed into the sump plug. Because sender - gauge calibration is the same (its not if you use an oil temp sensor) I am able to view oil temp on my water temp gauge using a toggle switch to flick from water to oil temp. Like Alex on track , I find SUMP oil temp at rising to 125 without oil cooler and 110 ish with an oil cooler. On road, my sump temps almost approach water temp at 80 after about 10 miles, but I can tape off the oil cooler if its really cold. I use Mobil 15/50 for 10 years on track with my Zetec and no issues arising from oil. Im about to refresh the engine after 35,000 miles so will be able to look at it closely for the first time - I may have to eat my hat but after 35,000 miles with no attention I cant complain!.

 

By the way, its not just viscosity that matters, its "lubricity" the ability to achieve and maintain a molecular film at higher temperatures - this data is not easily available. Bottom line is I would not run less than 5/50 or 15/50 synthetic for track use , the former being better at low temperatures if you are concerned about warm up . . . .

 

 

Paul

 

Zeeeeeeetec . . . . . .

[Alex Wong1697456877]

Mine is measured in low pressure side of the oil pump - arguably the coolest the oil gets would be here.

 

I think 5/40 is going to be the best bet for me.

[paul.davis]

Alex, might it be worth watching for vapour condensate in your catch pot? If 5/40 breaks starts to breakdown on track at high temp you may see more coming over . . . I noticed a difference between mobil 0/40 and 15/50 .

 

Paul

 

Zeeeeeeetec . . . . . .

[oilman]

Lubricity is one thing that all oils give, it's shear stability that's the most important thing and this is always related to the quality of the basestocks used which determines the level of Vi Improvers that are required.

 

Viscosity Index Improvers.

 

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.

 

Cheers

Simon

 

 

sales@opieoils.co.uk

[Sheds Moderator]

It would appear that a Laminova is a very good idea for getting oil temp up to 80/90C quickly on road and keeping it there under heavy load on track.

[Pierre Gillet]

Hé hé, it is exactly what I did despite my mates on the French forum calling it my Mamy Nova (in France a well known yogurt brand) ☹️

[Sheds Moderator]

Et ta refroidisseur de yaourt, ça marche? 😬

 

(UK trans: Does your yogurt cooler work then?)

[Pierre Gillet]

It works a treat Steve.

In fact the oil temp is generally lower than the water temp, on the road.

 

Pierre

[Bob Corb]

I agree with virtually everything you say apart from "This shows that a 5W/40 or a 10W/40 is perfectly adequate for all engines except those that run an unusually high temperature." The ability of the oil film to maintain an adequate oil film is dependant on the properties of the oil (viscosity and density ~ temperature) but also the pressure/force the bearing has to withstand.

 

For example the BMW M3 has extremely highly loaded big end bearings this is due mostly inertia of the piston and rod and the limited area available on the crankshaft (carryover part now in its last evolution). The oil temperature in the car will be tightly controlled and I cant believe a BM has that poor cooling yet they've seen fit to specify Castrol 10W/60 (this has changed recently from 5W30).

 

I am being a little pedantic (sorry) but I just thought I'd make the case for thicker oils too. So for most cars with a standard cranktrain running at similar to standard road car speeds (i.e. up to 7400 for K) I'd say that ...40 is still the way to go (as per Rover OE fill). At higher engine speeds you're in the unknown, Minister wont have done many bearing design calcs, they will just go by experience so in the extreme of an R500 I'd want a 50 grade. Preferably a "real" synthetic at that.

 

BC

[oilman]

Whilst I agree in part with what you say, you cannot generalise as 10w-60 is not suitable for all M3's.

 

In BMW's technical bulletin issued to the Dealers 10/04 they state catagorically that the 10w-60 recommendation is only applicable in certain engines. This is what they say:

 

BMW LL01 Viscosity 0w-30, 5w-30, 0w-40 and 5w-40 is approved for all BMW engines EXCEPT

 

M43/CNG, S54 and S62/E39 (up to 02/2000) where 10w-60 should be used.

 

They go on to clarify the S62/E39 recommendations as follows (bulletin GB-001-40):

 

Incorrect guidence is offered in relation to the correct operating fluids approved for BMW vehicles.

 

Please ensure that the operating fluids manual on TIS is consulted regularly as it contains accurate and up to date information on specified operating fluids.

 

An example of this is the approved oil for the S62/E39.

 

The S62/E39 up to 02/2000 are specified sae 10w-60 engine oils.

 

The S62/E39 02/2000 onwards is specified BMW LL01 sae 0w-40 (fully synthetic)

 

A check of section 3.0, 5.0 and 9.0 of the operating fluids manual confirms this.

 

So, whilst I agree with you in part, it's not the whole story and there are to my knowledge many BMW Dealers using the wrong oils as they clearly don't read the tech bulletins.

 

Hope this clarifies.

 

Cheers

Simon

 

sales@opieoils.co.uk

[Bob Corb]

S62 is a V8 in a pre 2003 M5. That engine doesn't rev anything like the E46 M3 (rev limit 7000rpm) whereas the M3 E46 revs on past peak power at 7900rpm. Its this high inertial loading which really hurts bearings. Of coarse with a new design you can get the bearing pressures down and therefore use a lower viscosity oil but its the bearing design which controls the choice of oil grade.

[oilman]

Bob, I don't disagree with you, I'm just quoting the Tech Bulletins I have in front of me verbatum.

 

Cheers

Simon

 

sales@opieoils.co.uk

[Bob Corb]

No worries Simon.

 

I'm still regretting not phoning you. Its all down to my bad planning. I bought 2 litres of Castrol SAF-XJ the other day from my local BMW dealer - £42 . Can you get it in smaller bottles?

[DaveMorris]

I didn't join in the debate as I run a x-flow. Not a "modern engine" in may senses of the word.

 

My problem is getting to grips with an engine whose oil pressure varies massively with revs and oil temp when compared to these more modern designs. I'm getting more and more paranoid looking at the oil press. instead of the road ahead, and dreaming up all sorts of problems as soon as the pressure moves.

 

At oil temperatures above 90degrees (achieved quite easily over the last few days) tickover pressure is abysmal.

 

Anyway - back to the modern brigade.