Oil - to change or not to change?

[Avocet]

I don't think I advocate a monograde anywhere. I have owned many air-cooled VWs, for which a monograde was originally specified, but I always used multigrades.

I would not use a 10W/40. These low viscosity oils are for one purpose only - fuel economy. 10W is not quite enough for a full hydrodynamic film and an old engine with perhaps some wear, copper-lead bearings and an unhardened crankshaft will not be happy. I would use 15w/40.

Sorry Vyv, I missed this. I don't know that much about lubricants but assumed that when the oil was hot, it behaved more like a 40 (which would be thicker than a straight 30 at the same temperature) and when it was cold, both a 15/40 and a 10/40 would be MUCH more viscous than a hot 30 monograde, so if there's enough for an adequate hydrodynamic film with a hot 30 monograde, then pretty much anything will be ok when cold?

 

[Lakesailor]

if the oil meets CF-4 it will meet CF as it encompasses that grade as it does,CC,CD specs

It seems that CF-4 is obsolete now. We are on to CF-5

API website Oil Guide

 

[Plevier]

It seems that CF-4 is obsolete now. We are on to CF-5

API website Oil Guide

Interesting.
Can't find CF-5 in your linked document though - did you mean CH-4 or have I overlooked something?

(I see a GF-5 replacing GF-4 but that's something different, diesel stuff is next page.)

 

[sailorman]

It seems that CF-4 is obsolete now. We are on to CF-5

API website Oil Guide

Oh no what ever nxt

 

[vyv_cox]

if the oil meets CF-4 it will meet CF as it encompasses that grade as it does,CC,CD specs

CF has a higher base number to enable it to cope with sulphur levels above 0.5%. CF4 has a lower TBN that is better suited to lower sulphur levels and cooler running, both of which result in less acidic oil chemistry.

A monograde oil is viscous at low temperatures, much less so at high. Multigrades have relatively lower viscosities when cold but relatively higher when hot. More wear occurs in the first few minutes of running than it does when hot oil is circulating freely. A good hydrodynamic film is needed to protect bearings in particular, but cams and tappets also. Low viscosity multigrade oils do not provide sufficient protection to older engine designs that use unhardened shafts etc and copper lead bearings.

 

[Avocet]

...but surely if the bulk of the wear occurs in the first few minutes, before the oil has got up to temperature, that suggests that the oil gives better protection at higher temperature (when it is thinner) and therefore the multigrade (being thinner when cold than the monograde) should give BETTER protection when cold? (Remember this engine is entirely splash-lubricated, there's no oil pump, so "circulation" in the conventional sense of the word doesn't really happen).

 

[vyv_cox]

...but surely if the bulk of the wear occurs in the first few minutes, before the oil has got up to temperature, that suggests that the oil gives better protection at higher temperature (when it is thinner) and therefore the multigrade (being thinner when cold than the monograde) should give BETTER protection when cold? (Remember this engine is entirely splash-lubricated, there's no oil pump, so "circulation" in the conventional sense of the word doesn't really happen).

I suggest you read what I wrote earlier more carefully. The multigrade will be thin at lower temperatures. Try shaking a tin of the modern 0W/10 and similar grades, it sounds like water in there! The only benefit in going less than 15W is fuel economy, at the expense of metal to metal contact.

Hydrodynamic lubrication does not need an oil pump. The pressure that separates the two surfaces is generated by the relative motion. Discovered by Beauchamp Tower in 1883. See http://www.tribology-abc.com/abc/tower.htm

 

[Avocet]

Well I THOUGHT I had?! Yes, I'd noticed that the low number multigrades are like pi55 when I shake the can - which is as I'd expect for a 5 or a 0 viscosity. (Actually, not really sure WHAT I expected for a "0" viscosity, but you get my point anyway...).

Now if I take a tin of straight 30 when cold, it feels much thicker. When I shake a tin of straight 30 at operating temperature, it feels much more like the 5 grade does when it's cold - all of which is as I'd expect.

I'd heard the generally accepted received wisdom that most engine wear occurs within the first few minutes of a cold start too, but I had ASSUMED (and maybe here's where I'm going wrong!) that the reason for this was that when the oil was cold and viscous, it didn't flow well, and therefore didn't provide optimum protection. Once warm (and less viscous), it flowed better and the hydrodynamic film could be maintained easily by the crank rotating relative to its plain bearings. Is that correct?

If so, I still keep coming back to the notion that the multigrade's lower viscosity when cold, is actually better for preventing engine wear than the straight grade (which, in order to maintain a decent viscosity when hot, needs to be much thicker when cold).

 

[Plevier]

May I intercede?
I think you are both saying the same thing BUT Vyv is saying don't go TOO thin or you swap the risk of oil not circulating for the risk of inadequate film.
The optimum for older simpler engines is 15-40.
I hope that's right!

Vyv have you noticed the bit about CF, CF-4 and CG-4 now being obsoleted by API and having to go to CH-4?

Well I THOUGHT I had?! Yes, I'd noticed that the low number multigrades are like pi55 when I shake the can - which is as I'd expect for a 5 or a 0 viscosity. (Actually, not really sure WHAT I expected for a "0" viscosity, but you get my point anyway...).

Now if I take a tin of straight 30 when cold, it feels much thicker. When I shake a tin of straight 30 at operating temperature, it feels much more like the 5 grade does when it's cold - all of which is as I'd expect.

I'd heard the generally accepted received wisdom that most engine wear occurs within the first few minutes of a cold start too, but I had ASSUMED (and maybe here's where I'm going wrong!) that the reason for this was that when the oil was cold and viscous, it didn't flow well, and therefore didn't provide optimum protection. Once warm (and less viscous), it flowed better and the hydrodynamic film could be maintained easily by the crank rotating relative to its plain bearings. Is that correct?

If so, I still keep coming back to the notion that the multigrade's lower viscosity when cold, is actually better for preventing engine wear than the straight grade (which, in order to maintain a decent viscosity when hot, needs to be much thicker when cold).

 

[Avocet]

I suppose what I need to know is what the viscosity of a straight 30 is at normal operating temperature. If that's less than that of a cold 10/40 I'm fine, I think!

 

[sailorman]

CF has a higher base number to enable it to cope with sulphur levels above 0.5%. CF4 has a lower TBN that is better suited to lower sulphur levels and cooler running, both of which result in less acidic oil chemistry.

A monograde oil is viscous at low temperatures, much less so at high. Multigrades have relatively lower viscosities when cold but relatively higher when hot. More wear occurs in the first few minutes of running than it does when hot oil is circulating freely. A good hydrodynamic film is needed to protect bearings in particular, but cams and tappets also. Low viscosity multigrade oils do not provide sufficient protection to older engine designs that use unhardened shafts etc and copper lead bearings.

as a matter of interest
when my Mondeo diesel last had a service,Ford had changed oil spec had gone from semi to fully synthetic oil.

 

[tinkicker0]

That would be when they changed from Formula E to Formula F.

To the guy with a splash fed plain bearing motor, it is pretty vital that you stick to the OE specification. Take your manual and get your oil made up at a blenders if it is no longer available.

You will need a far higher phosphorous /sulphur content than modern oils contain.

 

[vyv_cox]

I suppose what I need to know is what the viscosity of a straight 30 is at normal operating temperature. If that's less than that of a cold 10/40 I'm fine, I think!

Yes, Troubador has it right. A monograde will be viscous at low temperatures, which makes lubrication from start-up less effective. A multigrade will be thinner at low temperature, equivalent to a monograde 15 for a 15W/40. At operating temperature the 15W/40 will have the viscosity of a 40 monograde. In each case the multigrade offers advantages for your engine.

 

[longjohnsilver]

Yes, Troubador has it right. A monograde will be viscous at low temperatures, which makes lubrication from start-up less effective. A multigrade will be thinner at low temperature, equivalent to a monograde 15 for a 15W/40. At operating temperature the 15W/40 will have the viscosity of a 40 monograde. In each case the multigrade offers advantages for your engine.

Vyv, several years ago you recommended I use a 30 for my Ford Lehman 135 diesels, now approx 25 years old, when I posted that I was using Shell Rimula 15/40. Are you now saying that the 15/40 is more appropriate? In reality does it make much difference, I've been using Shell sae 30 since then.

 

[vyv_cox]

Vyv, several years ago you recommended I use a 30 for my Ford Lehman 135 diesels, now approx 25 years old, when I posted that I was using Shell Rimula 15/40. Are you now saying that the 15/40 is more appropriate? In reality does it make much difference, I've been using Shell sae 30 since then.

Are you sure I recommended it on the basis of the viscosity? The formulation of the various Rimula grades, and many other products, changes with time but the name remains the same. Current Rimula oils vary from semi-synthetic to highly refined base oils, some with significant additive packages. The API classification may be the reason I advised the monograde. Many engines do still use them, Bukh in particular.

 

[longjohnsilver]

Are you sure I recommended it on the basis of the viscosity? The formulation of the various Rimula grades, and many other products, changes with time but the name remains the same. Current Rimula oils vary from semi-synthetic to highly refined base oils, some with significant additive packages. The API classification may be the reason I advised the monograde. Many engines do still use them, Bukh in particular.

No, not sure on what basis you made your recommendation. But I did act on your advice as you obviously know much more about lubricants than I do. And I looked at the manual and that also recommends sae 30. But is 15/40 better? Don't pretend to understand all the pros and cons.

 

[jfkal]

Dont forget to change the filter too )

 

[Rossynant]

SAE 20/40 API CC/CD mineral, still can be obtained in countries where they don't want their tractors to be ruined
High grades can glaze cylinders in lower temperature, and that is common on sailboats, not running at max load...

 

[Latestarter1]

No, not sure on what basis you made your recommendation. But I did act on your advice as you obviously know much more about lubricants than I do. And I looked at the manual and that also recommends sae 30. But is 15/40 better? Don't pretend to understand all the pros and cons.

During late 70's early 80's during development of the Ford Dover lube service requirements for the older Dorset motor were brought into line i.e adoption of 15W40 lubricants Worldwide and at the same time we were able to revise drain interval upwards to take advantage of the newer lubes. Change was viewed by all Ford distributors as positive with one exception, the mariniser Lehman in the U.S who still insisted on publishing lube requirement as straight 30.

Sabre eventually took over Lehman, kicked out the cause of the problem, Bob Smith and published revised service topics. Smith still pops up on trawler sites promoting use of straight grade lube oils for Ford Dover/Dorset motors.

 

[Avocet]

Interesting point. Yes, I guess we also need to keep in mind the possibility that there's nothing more scientific behind a decision that someone in a position of seniority saying "because we've always done it this way"!