Destroying the OMD115 myths.

[isuzurover]

For some strange reason some people think that the oils used by the military are the best oil to use in a 4BD1(T). This is despite the fact that most army 4BD1(T)s did very few km compared to 4BD1(T)s in trucks.

However, that is neither here nor there. The myth we are destroying here is that a 20W60 diesel oil is equivalent to OMD115. The consensus seems to be that OMD115 is an SAE40 oil.

The attached graph shows the minimum and maximum viscosity for the SAE40 spec, together with a 15W40, 20W60 and Monograde 40 (Detroit diesel engine) oil.

EDIT: Updated graph to show SAE30 and SAE40 ranges, see document on next page showing that OMD115 is (or was) SAE30.



http://www.aulro.com/afvb/attachment...s-oil_vis3.jpg



http://www.aulro.com/afvb/attachment...s-oil_vis4.jpg

[isuzurover]

I also suspect that OMD115 was selected for commonality as it is required by the detroit diesels in the ASLAVs.

[workingonit]

Thanks Isuzu. Unfortunately I'm not familiar with the issue. Which oil are you supporting (assuming the 20W60)?

In this example the SAE40 is not actually from a can labelled OMD115 hence the '?' ?

[workingonit]

If you had asked me off the top of my head I would have said use the 15w40. From memory I tried a Penrite 20w40 in my troop carrier and it took some minutes for the oil pressure guage to drop to what I considered normal - I assume OK for the bearings but not sure what extra stress it puts on the pumping components - probably nothing to worry about!? Odd that 15w40 never gave the same initial high pressure guage reading as 20w40, given both start at 40.

[isuzurover]

Thanks Isuzu. Unfortunately I'm not familiar with the issue. Which oil are you supporting (assuming the 20W60)?

In this example the SAE40 is not actually from a can labelled OMD115 hence the '?' ?

There are a group of people on here who use 20W60 and 20W50 oils and argue that they are equivalent to OMD115.

I am showing here that this is not correct. As you say, a 15W40 oil is the closest to OMD115 spec.

There are also some on here/remlr who use monograde SAE40 oils as they believe that matches the OMD115 spec. IMHO that is just silly. If you live in FNQ or Darwin you may get away with a monograde oil, but everywhere else you are just asking for accelerated wear on startup. Plus monograde oils are really a dead end as far as R&D goes, multigrade oils have much better additive packages.

[Not_An_Abba_Fan]

If you had asked me off the top of my head I would have said use the 15w40. From memory I tried a Penrite 20w40 in my troop carrier and it took some minutes for the oil pressure guage to drop to what I considered normal - I assume OK for the bearings but not sure what extra stress it puts on the pumping components - probably nothing to worry about!? Odd that 15w40 never gave the same initial high pressure guage reading as 20w40, given both start at 40.

Other way around actually, the first number is the cold viscosity. The 20W40 will be a bit thicker cold than the 15W40.

[isuzurover]

Other way around actually, the first number is the cold viscosity. The 20W40 will be a bit thicker cold than the 15W40.

Yes that is correct. You can see from the graph above that the monograde oils have a steeper slope so are more viscous at low temperatures. Below 10 degrees they really start to deviate from the fitted line, and become even more viscous (even worse than the 20W).

[workingonit]

Thanks N.A.A.F. I originally thought as you described. A 'thin' (low viscosity) for cold starts, getting 'thicker' (higher in viscosity) to provide better protection to the bearings as the engine warmed up.

But when I looked at the graph I thought I must be wrong, as it seems the colder the engine the higher the viscosity and vice versa. Looking at wiki further confuses me quote for mongrade "A specific oil will have high viscosity when cold and a lower viscosity at the engine's operating temperature" but with additives "cause the multi-grade oil to have the viscosity of the base grade when cold and the viscosity of the second grade when hot"

I'm thinking rightly or wrongly that the graph presented is fine for monogrades ie dense when cold, but thin when hot. Wouldn't you expect a different line (more horizontal or curved) for multigrades than presented here given the viscosity is 'dynamic'?

[87County]

It has been reasonably well established that a 15W-40 diesel engine oil can be used in the engine, gearbox and tc of any military or civilian Isuzu engined 110. Castrol RX Super seems to be most frequently recommended but any oil with an equivalent rating can be used.

Quite straightforward really.

[isuzurover]

Thanks N.A.A.F. I originally thought as you described. A 'thin' (low viscosity) for cold starts, getting 'thicker' (higher in viscosity) to provide better protection to the bearings as the engine warmed up.

But when I looked at the graph I thought I must be wrong, as it seems the colder the engine the higher the viscosity and vice versa. Looking at wiki further confuses me quote for mongrade "A specific oil will have high viscosity when cold and a lower viscosity at the engine's operating temperature" but with additives "cause the multi-grade oil to have the viscosity of the base grade when cold and the viscosity of the second grade when hot"

I'm thinking rightly or wrongly that the graph presented is fine for monogrades ie dense when cold, but thin when hot. Wouldn't you expect a different line (more horizontal or curved) for multigrades than presented here given the viscosity is 'dynamic'?

All oils are thick (more viscous) when cold and thin (less viscous) when hot. However multigrade oils are blended to reduce the rate of viscosity increase as temperature decreases. That is why you see the 15W40 line crossing over the 3 monograde 40 lines. The difference looks small, however the y-axis is a log scale. Plus the difference gets more pronounced below 10oC.