Thread: Destroying the OMD115 myths.

Originally Posted by Mick_Marsh

OMD-115 facts:

Specification: MIL-L-2104E
NATO code: O-238
SAE Grade 30
API CDII
Viscosity: 9.7-12.5mm?/s @ 100?C
Viscosity Index (VI): 75 (min)
Pour Point: -18?C (max)
Flash Point COC: 220?C (min)

NSN 205l : 9150-66-017-3041
NSN 20l : 9150-66-089-6558



So, what does that tell us?

So now you are saying OMD115 is SAE30 instead of SAE40?

That plot tells us nothing because whomever plotted it hasn't used a log scale for the y-axis. Have a look at my plots which show the same data.

I really think we are getting into a lather over nothing!
Yes, it might be nice to know the details, but essentially we are talking about a 1990 model truck engine. It does not have ceramic bearings or berrylium lobes, - it's just a diesel truck engine!
Normal diesel engine oil, like Castrol RX will do me.

Originally Posted by Aussie Jeepster

I really think we are getting into a lather over nothing!
Yes, it might be nice to know the details, but essentially we are talking about a 1990 model truck engine. It does not have ceramic bearings or berrylium lobes, - it's just a diesel truck engine!
Normal diesel engine oil, like Castrol RX will do me.

Yes it is all a bit silly. However a lot of people seem to want to match the military oil spec (OMD115). This is despite the fact that every oil supplier recommends a 15W40 oil (e.g. RX Super) for the 4BD1(T). The only exception to this is Penrite which recommend a 20W60 for a 4BD1(T) in a landie but a 15W50 for the same engine in a truck.

Depending on which document you look at, OMD115 is either a straight 30 or a straight 40. Which means that any XXW40 oil will be a match at operating temperatures.

Mick Marsh (who has said he uses 25W70) is trying to claim that this oil meets OMD115 because the viscosity curves match up at low temperatures - which is actually a really bad thing!!!

Originally Posted by isuzurover

Yes it is all a bit silly.

.....

Mick Marsh (who has said he uses 25W70) is trying to claim that this oil meets OMD115 because the viscosity curves match up at low temperatures - which is actually a really bad thing!!!

hmmm, interesting

Well IMHO....

I dont think its all a bit silly or even getting carried away, its staying on topic and at the end of the day, people can put whatever they want in their own vehicle.

If we look at the data from isuzurover and Mick_Marsh, comparing the MIL spec OMD-115 (keep in mind thats not a product, its a required specification that has been made by the military and nothing more) we can deduct and see the following:

*A mono or single weight SAE 30 engine oil meets the spec at the SAE standard test at 100 deg C (in fact it exceeds the spec).
*At the lower temperature test of 40 deg C it also does well.
*the multi grade 15W40 actually doesnt do as well which would steer me to the obvious better choice of using a 10W30, or 10W40 or even better a 5W40 engine oil.
*Keep in mind a multi grade engine oil is always going to do better, on cold engine start up, which is the most critical wear issue on an engine, you need that good/instant flow of engine oil to components.
*Sure if you run a fleet of trucks and use a diesel engine oil such as Shell Rimula, then throwing it in your Isuzu powered Land Rover 110 is going to be fine, keep in mind truck engines are subjected too far greater stresses than an engine in a little 2 ton Land Rover.

*The big fat elephant in the room that makes the MIL spec OMD-115 fall on its arse is the requirement of a VI rating of only 75 ????? thats laughable, A VERY BASIC EXPLANATION OF "VI" rating, It is the rate of change of viscosity between two temperatures. The lower the VI rating, the more the drop in viscosity as the oil warms up. The higher the VI rating, the less the drop in viscosity as the oil warms up., so the higher the VI rating the better. The average for modern multi grade engine oil is round 130 - 150, making the requirement of a VI rating of 75 look like something from the 1950's or 1960's.

IMHO, so take this one as you will...
I use on all customers Isuzu powered 110's, Penrite HPR DIESEL 5 5W40 semi synthetic (actually I use it on all 110 & Defenders), it has the good flow properties of a SAE 5 on that oh so critical cold engine start up but performs as a SAE 40 engine oil at the standard 100 deg C temperatures.

Which always makes the odd owner or mechanic say that a 5W40 multi grade engine oil is too thin to use on these old engines, that my friends is simply a myth that cant be supported by factual information.

All the above is some very very basic info and I have left out a LOT and I mean a hell of a LOT of information, this is oil chemical science, the more you get into it, the more your head will spin.

Just a starting point, the more you read and get into it, the more you will find:
https://en.wikipedia.org/wiki/Motor_oil
Motor Oil Viscosity Grades Explained in Layman's Terms
Basics of viscosity and the flow behavior of liquids
Oil Viscosity Explained
What Every Motorist Should Know About Motor Oil

Regards
Daz

I think the biggest problem a lot of people have is that they don't understand the differences between SAE winter and summer (hot/cold) ratings. It is a bit counterintuitive that the SAE 0-25(W) is a lower number than the summer number. So many people think a 20W60 the 20 is actually the summer rating.

If we rated them by kinematic viscosity the OMD115 would be a 1600(c)12(h) or similar (i.e. 1600 mm2s-1 during cold starts and 12 at operating temp). I am using c for cold and h for hot here so as not to confuse the W for winter in the SAE rating system.

With a rating system like that people would choose the oil that has the lowest cold viscosity (i.e. a 0W or 5W - which is about a 50(c)12(h) in kinematic viscosity). Because a viscosity of 50 (mm2s-1) or so is much closer to the 12 (mm2s-1) you want to have at operating temperature.

Just curious as to why so many are fascinated with what the military used.

Have these same people tried talking to an "Isuzu" dealership to see what Isuzu themselves used in the day?????
Id almost bet a left nut it wasnt what the military used.

If I get a chance tomorrow I'll contact a dealer

Originally Posted by Trigger82

Just curious as to why so many are fascinated with what the military used.

Good question.

Have these same people tried talking to an "Isuzu" dealership to see what Isuzu themselves used in the day?????
Id almost bet a left nut it wasnt what the military used.

If I get a chance tomorrow I'll contact a dealer

My 1988 Isuzu WS manual specifies 10W30.