Is logic of thick oil for older cars falling apart

[TechnoLoGs]

Originally Posted By: aquariuscsm
Originally Posted By: Brit33
What to use in an old boxer engine then? Specs 10w40 or 10w50!
Clearances are not tight like on a modern engine.
Block flexes at high revs.

I use 15w50. Would you use anything thinner? 5w40 maybe.
Idle hot 10psi but at higher revs it reaches a healthy 60 psi.



5W20 wouldn't protect that engine??



This an honest question, and founding principle of BITOG.........

I think Dr. Haas's 0W-20s, which are, in fact, more like light-mid 30-weights if HTHS is used (the only way his writings make sense,) would, maybe...

But I don't know....................................

I summon Leviathan CATERHAM.

 

[Brit33]

Just come back from my mechanics.(he has his workshop here in Uruguay but spent many years working in Europe for rally teams)

My alfa was in due to a stuck valve which cleared itself up after a few mins in the garage!!

had the water pump, tensioners, belts and driveshaft gaitor changed.


But we started talking about oil.

I asked what he recommended.

One word came out Castrol!
which grade?

This one! he pulled out 10w60 TWS

He uses it in his rally cars (such as the Evo) and his street cars. The best he had ever used.
He services many old cars, jags, alfas, MG, Peugeot etc


Too thick for my old alfa?
No not at all as long as you OP/temp is all within good limits. it provides excellent protection.

I just took it out for motul 300v. ah french oil no thanks!! LOL

 

[GordonC]

Originally Posted By: Brit33
What to use in an old boxer engine then? Specs 10w40 or 10w50!
Clearances are not tight like on a modern engine.
Block flexes at high revs.

I use 15w50. Would you use anything thinner? 5w40 maybe.
Idle hot 10psi but at higher revs it reaches a healthy 60 psi.



I read through this thread, and the post above is the only one that hints at something other than modern vs old oil determining what viscosity of modern oil to use.

The physical engine itself is designed for a certain oil viscosity - bearing clearances especially, along with oil passages and flow rates, are all designed for specific viscosities. Older engines, or high performance engines, often had bearing clearances much larger than modern engines manufactured on much higher tolerance production machinery that can mass produce parts to much greater precision.

Modern vs old oil doesn't affect whether an engine needs a 50 weight oil when warm - bearing clearances, oil pump flow rates and pressure, determine the oil viscosity requirement. An engine with 'loose' bearing clearances will require higher oil pressure, higher flow rates, or thicker viscosity to maintain the bearing oil film. Running a modern thin oil in an engine designed for a thick oil can have catastrophic consequences.

I recently bought a 1984 Ferrari 308 GTS quattrovalvole - it has a 3 litre V8, and factory spec was 15W50 Agip oil. Apparently that was a synthetic oil, but the point is that the engine was designed and built to run 50 weight oil when warm, and requires normal oil pressure when warm and at 6000 rpm to be 85 psi. I use Castrol Edge 5W50 synthetic in it, I could use Mobil1 15W50 etc - but there's no way I'd go less than 50 weight in that engine.

IF I had a genius engine rebuilder go through that engine and change the bearing clearances to be tighter on the crank journals, rod bearings, camshaft bearings, etc, then I'd run a thinner oil - and the genius engine rebuilder would be able to tell me exactly what viscosity would be required for the bearing clearances he used when rebuilding/redesigning that engine. The same would apply to any engine, modern or vintage, where a significant change to oil viscosity was desired, or a significant change to bearing clearance design might require a change to the oil viscosity used.

 

[Shannow]

GordonC, most excellent post.

Ford's Quaddrillion mile test through the deserts of Alberabaran are only applicable to Ford's design, engineering assessments and testing...Honda back-speccing to 20s for "certain" models is similarly, application specific, by the people who know what the parameters that they used in the design were in the first place.

A modern oil of x HTHS will provide the same film thickness as an old one, and it's the viscosity that provides the hydrodynamic lubrication, not oil pressure or volume.

 

[CATERHAM]

GordonC your 308 has been back-spec'd by Ferrari for Shell Helix 5W-40 which is a reasonably light 40wt oil.
The 50wt oils you've mentioned are unnecessarily heavy for your car. The following is a rather old UOA of M1 SL 0W-40 in an '87 328:

http://www.bobistheoilguy.com/forums/ubb...3160#Post253160

 

[CATERHAM]

Originally Posted By: aquariuscsm
Originally Posted By: 901Memphis

Funny how you said that though I notice you use 5w50 synthetic not 15w50 conventional in your Z.


The Syntec is actually thicker at operating temps than M1 15W50 and GTX 20W50 according to the pds sheets.

Syntec 5W50 @100=18.5
M1 15W50 @100=18
GTX 20W50 @100=18.09

I've used all three of those oils and based on actual oil pressure figures the low VI GTX is by far the heaviest at operating temp's.
The lightest is Syntec 5W-50.

Just another example of why KV100 spec' will not tell you which oils are heavier or lighter at operating temp's.
If you can dig up the HTHSV and VI spec's then you can better predict the operational viscosities of motor oils.

 

[Brit33]

Originally Posted By: GordonC
Originally Posted By: Brit33
What to use in an old boxer engine then? Specs 10w40 or 10w50!
Clearances are not tight like on a modern engine.
Block flexes at high revs.

I use 15w50. Would you use anything thinner? 5w40 maybe.
Idle hot 10psi but at higher revs it reaches a healthy 60 psi.



I read through this thread, and the post above is the only one that hints at something other than modern vs old oil determining what viscosity of modern oil to use.

The physical engine itself is designed for a certain oil viscosity - bearing clearances especially, along with oil passages and flow rates, are all designed for specific viscosities. Older engines, or high performance engines, often had bearing clearances much larger than modern engines manufactured on much higher tolerance production machinery that can mass produce parts to much greater precision.

Modern vs old oil doesn't affect whether an engine needs a 50 weight oil when warm - bearing clearances, oil pump flow rates and pressure, determine the oil viscosity requirement. An engine with 'loose' bearing clearances will require higher oil pressure, higher flow rates, or thicker viscosity to maintain the bearing oil film. Running a modern thin oil in an engine designed for a thick oil can have catastrophic consequences.

I recently bought a 1984 Ferrari 308 GTS quattrovalvole - it has a 3 litre V8, and factory spec was 15W50 Agip oil. Apparently that was a synthetic oil, but the point is that the engine was designed and built to run 50 weight oil when warm, and requires normal oil pressure when warm and at 6000 rpm to be 85 psi. I use Castrol Edge 5W50 synthetic in it, I could use Mobil1 15W50 etc - but there's no way I'd go less than 50 weight in that engine.

IF I had a genius engine rebuilder go through that engine and change the bearing clearances to be tighter on the crank journals, rod bearings, camshaft bearings, etc, then I'd run a thinner oil - and the genius engine rebuilder would be able to tell me exactly what viscosity would be required for the bearing clearances he used when rebuilding/redesigning that engine. The same would apply to any engine, modern or vintage, where a significant change to oil viscosity was desired, or a significant change to bearing clearance design might require a change to the oil viscosity used.


excellent write up!
Yes the alfa boxer engine is a flexible block and so cannot be run with tight clearances. So your explanation makes perfect sense. That is why they recommend a 40 or 50wt min.
so a 10w60 would be fine for an older engine with even looser clearances.
mind you with the newer 155 twin spark a 10w60 is recommended now due to the amount of heat it produces. totally different engine altogether.

regards

 

[Ken2]

From Gordon's excellent posting: "The physical engine itself is designed for a certain oil viscosity - bearing clearances especially"

In addition, if there is wear the oil viscosity needs to be suitable for the actual clearances today. Generally speaking, match the viscosity to the clearances. If there are bigger clearances increase the viscosity to suit.

 

[CATERHAM]

Originally Posted By: Ken2
"The physical engine itself is designed for a certain oil viscosity - bearing clearances especially"

In addition, if there is wear the oil viscosity needs to be suitable for the actual clearances today. Generally speaking, match the viscosity to the clearances. If there are bigger clearances increase the viscosity to suit.

Yes the clearances determine the required viscosity but that does not necessarily mean a heavy oil grade should be used.
My '86 Porsche 928 is was originally spec'd for every grade from 5W-20 to 20W-50 based on ambient temp's and how the vehicle is driven. What the manufacturer is really trying to predict is the operational viscosity for the engine and the single biggest factor affecting viscosity is oil temperature.
With the advent of more advanced high VI motor oils Porsche now spec's just one grade, 0W-40 for all models back-dated 30 years.

 

[pscholte]

Originally Posted By: CATERHAM
Originally Posted By: Ken2
"The physical engine itself is designed for a certain oil viscosity - bearing clearances especially"

In addition, if there is wear the oil viscosity needs to be suitable for the actual clearances today. Generally speaking, match the viscosity to the clearances. If there are bigger clearances increase the viscosity to suit.

Yes the clearances determine the required viscosity but that does not necessarily mean a heavy oil grade should be used.
My '86 Porsche 928 is was originally spec'd for every grade from 5W-20 to 20W-50 based on ambient temp's and how the vehicle is driven. What the manufacturer is really trying to predict is the operational viscosity for the engine and the single biggest factor affecting viscosity is oil temperature.
With the advent of more advanced high VI motor oils Porsche now spec's just one grade, 0W-40 for all models back-dated 30 years.


Please restate what parameters you considered when formulating your blend and why you only use it in the 928 and the Bimmer but with different 0W-20 blenders. Thanks.