Everything you wanted to know about Oil (but didn't know you did)

[Peter Cobbold]

Hi Pete,

oddly enough that is not on the back of the Halfords Classic oil can

 

Roger

Roger,

I'll write to them suggesting a simplified form of words: "Caution: this oil is not going to protect a TR engine at screaming rpm."

 

That better?

Peter

[Peter Cobbold]

a 10-60 is supposed to be thicker than a 50W oil at higher temp,

 

In fact, if I bung a 5/50 in the MX, it gives moer pressure than the RS 10-60 did.

but by all the blurb, the 60W should give moer.

 

M

Marcus, I think the viscosity rating system allows a range of values for each grade. So the actaul viscocities of 50 and 60 may well overlap. Peter

[RogerH]

Thanks Pete,

 

 

Roger

[Cew]

+1 Roger.

The evidence is that our engines have managed to survive very well for many decades of using various mineral-based multigrades. If it were otherwise, this forum would be swamped by talk about premature engine failures from using the stuff. Perhaps one should view any information/opinion found on the internet with a due degree of scepticism, if it contradicts experience?

I agree with Darren that 'Which Oil' is a good and informative book for anyone wanting to understand motor oils and is written by someone who actually runs old cars.

 

Rob

Large commercial truck engines regularly exceed 2 million kms without rebuilds or using excessive amounts of oil,using (usually) a 10w30 oil.Obviously there will be exceptions,but just how many of our cars will have achieved anywhere near that mileage over their lifetime. I think that my car will probably see me out on what it has always been used to i.e. a multigrade oil changed regularly.

[oldtuckunder]

 

In fact, if I bung a 5/50 in the MX, it gives moer pressure than the RS 10-60 did.

but by all the blurb, the 60W should give moer.

 

 

Dont mix up W and non W scales, one is based on low temperature viscosity and the other at high temperature viscosity.

 

As Peter says there is overlap

 

For an interesting overview look at Table 5 in the following (by a different author)

 

http://www.bobistheoilguy.com/putting-the-simple-back-into-viscosity/

 

Alan

[Eddie Cairns]

Guys with regards to th 10W 60 oil if you look on the bobstheoilguy forum on used oil analysis posts you will find that the 60 grade oils loose their viscosity very quickly compared to something like Mobil1 0w/40 which holds on to it's viscosity long term.

[GT6M]

Dont mix up w and non w scales, !!!

what ye on aboot,, both oils are a 2 number, so a 2 number cant be a W and a non W oil.!!

 

And,

 

Temperature
The viscosity of a lubricant changes with temperature – in almost all cases, as the temperature increases, the viscosity decreases; and – conversely – as the temperature decreases, the viscosity increases. To select the proper lubricant for a given application, the viscosity of the fluid must be high enough that it provides an adequate lubricating film, but not so high that friction within the lubrication film is excessive. Therefore, when a piece of equipment must be started or operated at either temperature extreme – hot or cold – the proper viscosity must be considered.

 

, this is what I was saying, but in practice the 10/60 RS did nae live up to its job

it did,nt seem to thicken up, hence the low oil pressure.

the 5/50, seems to thicken up, as seen by higher oil pressure.

 

 

And as Eddie says, Ive also read on tech blurbs, that oils with a bigg gap between the 2 numbers, brek doon alott faster, some moer so than others.

 

All oils with 2 numbers set of as the lower number

IE, a 10/60 is just a 10 oil, but upposed to thicken up when hot , due to the modyfiers in it.

So when it breks doon, it reverts to a 10 oil, which is what I think i was finding with the RS.

 

yer 20 / 50 oils are just a 20W.

 

thats why, when ye change the olde hot engine oil, it comes oot like very thin pish,

its reverted back to its lowest number.

 

A good case was/ is the Sonic 20/50 oil I tried,

its a modern LM rated oil, but for some reason its got double the ZDDP as older 20/50 oils.

tried this to stop me cams wearing oot.

 

BUTT, this oil, after 300-400 miles brok doon so fast, it sent the oil gauge dropping too

This was backed up by others who had tried it too.

 

the Penrite oil seems to hold up v v well, as other on here say they use.

was lasting 2000 miles ish, befoer thing went ping in the engine

 

oqa the last 2 yers or so got to find oot that when the oils going off, and loosing its thickening abilities,

then the oil thats thinner gets thru the rings, and meks yer engine pink, due to oil dilation of the fuel,

 

The RS 10 60 did this act after aboot 300 miles,

but then, a 11.1 comp ratio shows things up moer than a lower one will.

 

But I wouldnt run a modern low ZDDP oil in a flat tappet engine, askin for trouble

as lots have found out. the modern metals are up to it, but no the older ones.

 

 

M

[oldtuckunder]

 

A good site and forum.

 

Have you ordered your Blackstones used oil analysis sample kit yet.

 

Ah with further reading I now understand, The used oil analysis forum is full of very interesting results (only in america would you get thousands of people spending money to have their old oil tested to publish the results) but its very interesting the conclusions that can be drawn. Interesting that so many modern semi and full synthetics have as much Molyb and Zinc in them.

[littlejim]

I used to get lent an old banger over Xmas by the Kiwi vets I boarded with during Uni. (They went back to the long white cloud.)

The banger used to get halfway to the 'Gong before the oil pressure dropped to 0. by then the temperature made it ideal for lubricating according to Dr Haas, but alas bugger all was getting pumped throught the big ends. the noises indicated lack of lubrication.

About 45 minutes of nose picking and admiring the view, at Maddens Plains, and it had cooled down and thickened up to Haas's non lubricating viscosity, but the gauge read pressure again and the noises stopped.

Sometimes a beautiful looking theory can distract you from reality. Especially if you throw a few tables or charts in.

Edited April 25, 2015 by littlejim

[Peter Cobbold]

In my quest to find out what's happening to fuel mixtures in a CD carb

Alan, Intriguing..... the oil in the damper should only affect the transient enrichment upon going to wot. You getting odd measurements of AFR? Peter

[oldtuckunder]

Alan, Intriguing..... the oil in the damper should only affect the transient enrichment upon going to wot. You getting odd measurements of AFR? Peter

 

Hi Peter

 

Sorry just spent half an hour on an indepth reply to this, and then the "F**********" Forum software threw an spurious html error and lost the lot when I hit post, will try and find the will power to recreate tomorrow.

 

Alan

[Motorsport Mickey]

Happened to me so many times now I copy the reply before trying to post it.

 

Mick Richards

[Peter Cobbold]

Yes it only takes one " go back one page" to look at an earlier post in a thread........... and the whole lot is lost.

 

I post, then go back, then edit, post again.....re-edit.

 

Infuriating.

 

Peter

[RogerH]

Copy & paste

 

Roger

[oldtuckunder]

Alan, Intriguing..... the oil in the damper should only affect the transient enrichment upon going to wot. You getting odd measurements of AFR? Peter

Sorry for delay, but rather than try and repost a subjective report, I thought I'd wait until I had reconnected the data logger and also had the Electronic Taco installed (to make it easier to cross ref between what I could see when driving and what the log said afterwards) NB Nice mechanical to electronic conversion by JDO, quick turnaround and gets the readings smack on above 2K RPM (apparently most people want them accurate at idle (but who spends any time there ))

 

Anyway I don't have time to post the full story (will find time in the next day or 2) so thought as a picture is worth a thousand words (I'd find a few old ones to delete to make room for this one ) Enjoy...

 

NB the difference between the best of the rest and the best was how far I was outside my bogey time at Gurston, now need to test and see if there is any impact on the flat. Oh the vertical blue bars are added to exactly mark the time between 3000 and 4000 rpm points

 

 

For those interested all the logs were taken over an hour at the same location, starting with the thinnest oil first, do a test run, remove damper suck out oil, flush with carb cleaner, suck out cleaner, fill with measured quantity of new oil, repeat test run, repeat....

Edited May 3, 2015 by oldtuckunder

[Peter Cobbold]

Alan

I'm finishing off a long blog post that covers how SUs work. But transients are impossible to model...

Will get back when I've assimilated your data - looks like there's a big lean spike for most of the damper fluids.

Peter

[oldtuckunder]

looks like there's a big lean spike for most of the damper fluids.

Peter

 

No it goes super rich (and stays there) just after WOT, the difference between 85-140 and the others is that it just keeps the AFR above 11 (which seems to be a critical ratio) where it can develop power accelerate and pull out (notice the AFR increasing as the revs rise above 4K) it seems that below 11 the super rich condition doesn't develop much power (feels sounds like a misfire) so the revs only gently climb. It doesn't show it in these traces but with the thinner oils if you just hang in there with your foot to the floor you gradually climb between 3k - 4k at which point magically? the AFR starts climbing again and as soon as it gets over 11 it takes off like a rocket again, the 85-140 "just" keeps it high enough so that the super rich flutter misfire doesn't start. With the thinner oils I also discovered that if you lift whilst in the middle of the misfire revs and then WOTagain it also lifts the AFR and then doesn't dive so deep on WOT so the power is better and you get to the critical 4K point without the flutter misfire. NB as lifting should drop the piston this tends to imply that the air piston is lifting too fast with the thinner oils and the 85-140 is just holding down long enough to keep the AFR above critical.

 

And YES I know we all need to know where the air piston is, but I got sidetracked from that project over the winter.

 

And do remember this is on a hill, on the flat even with the thinner oils the acceleration (time) between 3k and 4k is so quick and there is far less power required that their isn't time for it to go over rich. What I don't know yet is if on the flat the thicker oil actually slows acceleration.

[Peter Cobbold]

..I got the colours confused, rich it is.

 

So it running too rich a long time after the oil will have had any damping effect.

.

 

My best guess based upon SU calculations is the piston is fully lifted at wot from 2.5krpm upwards

In that condtion increasing the air flow increases the fuel flow in step with one another. ***

That means the mixture stays constant, which is what you record.

So try thickening the needle tip. If you want to get to AFR 13 down from 10 you need to reduce the are of the fuel in the jet by about one third.

Try solder ?

 

Peter

 

*** I guess from the data you have decent trumpets fitted? If not, the mixture will go much richer towards max rpm, it wont stay constant.

Edited May 3, 2015 by Peter Cobbold

[oldtuckunder]

 

So it running too rich a long time after the oil will have had any damping effect.

.

 

With thin oil yes with the 85-140 I think not

 

My best guess based upon SU calculations is the piston is fully lifted at wot from 2.5krpm upwards

In that condtion increasing the air flow increases the fuel flow in step with one another. ***

 

I think not, I could be at quite a light throttle opening and low piston lift at 2.5/3k and then go WOT the piston doesn't instantly go full lift

 

 

 

So try thickening the needle tip. If you want to get to AFR 13 down from 10 you need to reduce the are of the fuel in the jet by about one third.

Try solder ?

.

 

Can't do that by the time I get to 4k+ at WOT the AFR's are climbing nicely back into the 12's/13's and I'm going like a rocket again Now by that time I think I really do have full lift and certainly don't need a larger needle, I can't confirm what the AFR's do if I hold WOT above this point as I hit the 6.5k rev limit so quickly that I have to lift.

 

Alan

[Peter Cobbold]

Alan,

Its very odd. If the needle is not fully lifted at wot at 2.5 to 4krpm it should be possible to get rid fo the AFR 10 with a needle that is leaner in the right position.Try solder there.

Once the piston is at max lift the mixture will stay near constant at higher rpm. But your's is getting leaner.. Odd.

Peter

[oldtuckunder]

Alan,

Its very odd. If the needle is not fully lifted at wot at 2.5 to 4krpm it should be possible to get rid fo the AFR 10 with a needle that is leaner in the right position.Try solder there.

Once the piston is at max lift the mixture will stay near constant at higher rpm. But your's is getting leaner.. Odd.

Peter

 

I think the design problem is when full lift is reached, if full lift if reached at 3k (i.e. smallest needle diameter) then the engine is only sucking half as much air as required at 6k with the same needle/jet gap, so if the mixture is right at 6k what is it at 3k?

 

Theoretically you only want max lift at max rpm?

 

What we do know although not quantatively is that strange things happen at partial lift, i.e. same volume of air being sucked through a smaller lift (i.e. less needle/jet gap) can give a richer mixture than the same volume of air being drawn through a larger lift (i.e. more needle/jet gap).

 

Alan

[Peter Cobbold]

 

I think the design problem is when full lift is reached, if full lift if reached at 3k (i.e. smallest needle diameter) then the engine is only sucking half as much air as required at 6k with the same needle/jet gap, so if the mixture is right at 6k what is it at 3k?

 

Theoretically you only want max lift at max rpm?

 

What we do know although not quantatively is that strange things happen at partial lift, i.e. same volume of air being sucked through a smaller lift (i.e. less needle/jet gap) can give a richer mixture than the same volume of air being drawn through a larger lift (i.e. more needle/jet gap).

 

Alan

Alan

I cant get the pdf on the SU workings loaded onto the blog.

PM me with your email address and I'll email it to you. If you lilke.

 

Once the piston is fully lifted any further increase in air flow will still give the same AFR. Its because the formulae descrbing choke tube depression and fuel flow up the jet both go hand in hand, both are square law with air flow. BUT that will only happen with a carb mouth that is well rounded, with good trumpet design. If it is not, as air flows rise another pressure drop appears there and that adds to the choke tube depression and mixture will go richer with higher rpm.

 

^^^thats not in any books on SU or CD carbs I've read, but I am pretty sure its right.

 

So i dont think you do need to wait for max power to have max lift, the piston could be fully up at much lower power. If its full up at 3k the mixture will be the same at 6k, providing the mouth entry loss is small.

Its all in the pdf, but its not an easy read I'm afraid. It wasn't easy sorting out what is happening.....

.

""What we do know although not quantatively is that strange things happen at partial lift, i.e. same volume of air being sucked through a smaller lift (i.e. less needle/jet gap) can give a richer mixture than the same volume of air being drawn through a larger lift (i.e. more needle/jet gap).""

Can you be sure the piston is at part lift. I'll suugest an alternative, its fully up at 2.5 giving constant AFR to 4krpm as oultined above. And at higher powers above 4krpm fuel supply becomes slower so it gradually leans.

 

The pdf will show how to do measure the carb and do the calculations.

 

Peter

Edited May 3, 2015 by Peter Cobbold