Posted to Technical Discussion Forum on 4/23/2014
Fun with Diesel Exhaust Fluid
Hi fellow TDFers.
Recently, the specification values provided for Diesel
Exhaust Fluid (DEF) in GM eSI were questioned, specifically
as related to this thread by Paul Johnson.
The post and ensuing thread discussed possible reasons why a
DEF system pump failure was not covered under the vehicle
manufacturer warranty, because the recorded value for the
vehicle was far below the specifications for DEF and the
system was considered to have been contaminated with water.
Of concern was testing methods and accuracy, what equipment
was used, whether the technician knew how to use it and why
the cost of repair might have been customer pay on such a
low mileage vehicle.
Rather than focus on the possibilities of honesty/dishonesty
or competency/incompetency which are quite plausible, the
real interest was how the numbers were achieved and with
what tools and tests. There are on-vehicle systems tests to
run when DEF quality issues are identified, but the concern
of what hand-held tools are generally used in a GM
Having graced those service bays for many years, I am quite
familiar with most of the tools that have been around for
some time, although correlating exact tool numbers can be a
little difficult without a full description.
Of particular interest, was the fact that GM specifications
in eSI, listed the acceptable range for DEF as 1.310-1.3843
@ 20º C (68º F). Since pure water is identified as
being 1.3330, there was definitely some confusion.
Reviewing DEF specs from a number of supplier sources,
confirmed that pure DEF specifications have a Refractive
Index range of 1.3814-1.3843. I had encountered this some
time ago, when the measurement issue was discovered, by
another instructor and the numbers didn't jibe, but I didn't
pursue it any further than making a mental note. It seems
that when using refractive index to display specific gravity
there is some difference that is just beyond my need to
So, I sent a memo to my GM contacts that quietl founds its
way across various brand quality managers desks to an
individual charged with investigating. The results of his
research, supported a change in the listed specifications
for Duramax and Cruze diesel application documents in eSI
this morning. Since eSI documents are live, updates can be
effected quite quickly, often within 24 hours.
Fast forward to the end of my work day this afternoon. Armed
with the Leica refractometer from my program which was
exactly the same model as supplied to the GM dealership
where I worked for many years, I stopped in at the GM
training centre to gather more information to hopefully
better understand where the errors or anomalies in the
specifications arose from.
Since I also discovered that there were also anomalies in
the ratio of de-ionized water to urea in SI, reference to
the actual percentages of de-ionized water to urea has now
I had the opportunity to measure this ACDelco supplied DEF
[Yara DEF] used in the Duramax course and also some
YARA DEF. The latter fell off the back of a truck, quite
literally and was picked up off the highway by my co-worker.
[YARA DEF] [Yara DEF].
The plan was to gather information by measuring both DEF
samples using the Leica refractometer, Reichert
refractometer and the Kent-Moore supplied Adblue DEF
refractometer to compare readings in an effort to make sense
of the numbers.
First things first, exploring these refractometers brings to
my attention that the Kent-Moore refractometer [Samples
for testing] has an AdBlue Urea scale, with a waterline
set at 20 º C and a scale that reads from 15% to 40%.
Sorry, it is near impossible to take a photo of the scale.
There are plenty of sources for images of the DEF
Hmmm, none of the testing in eSI lists testing using the
percentage scale. This refractometer was supplied for
training. I didn't see anywhere in diagnostics any range for
urea. The only range reference had been the values in
Reading about refractometers versus specific gravity testing
of various fluids (relative density), appears to identify
that there is some variance in values. Searching the
Internet, I discovered that there are specific gravity
floats available for just about any imaginable fluid. I'll
keep this in mind later during testing. I'm simply
attempting to identify if and where the error is.
Testing all of the refractometers to ensure calibration
accuracy at 20º C in my home kitchen science experiment
this afternoon yielded accurate calibration to the water
lines, using the calibration de-ionized water sample "D" in
the temperature controlled environment. [Temperature]
Outside temperature value was in the kitchen.
Since Paul Johnson had wondered what the differences might
be between tap water and de-ionized water, I included a
couple of extra samples.
So, over to the kitchen table , set up with the following
samples in clean glass egg cups, were Eggzibit "A" from our
kitchen water cooler (sorry, I couldn't resist the pun) ,
Exhibit "B" Municipal tap water, Exhibit "C" YARA Air1 DEF
and Exhibit "D", the de-ionized calibration water from the
Kent Moore DEF refractometer kit.
Prior testing of both the ACDelco and Yara DEF samples had
resulted in identical measurements of exactly 32.5% to
specifications. So, for this test exhibit "C", I used the
Yara DEF. So, it appeared that when tested with the DEF
refractometer, the sample met specifications exactly.
Since the Leica and Reichert Battery and Coolant
refractometers tested both the same, the Leica was used for
the tests. All of the water samples tested exactly the same,
to the calibration line, including the Kent Moore DEF
refractometer water line.
Testing DEF using the Leica refractometer yielded 1315 which
might possibly support why the GM eSI specification for DEF
was originally listed as 1.310 -1.3843. Note: On
refractometers used for specific gravity measurements, it is
very common to leave the decimal place out for ease of
viewing. so, 1315 = 1.315, which is not far from the
specification previously listed at 1.310.
So, I now wonder if when DEF was first tested using a
refractometer, if one of these battery and coolant
refractometers was used, resulting in the lower specified
number in eSI, than that of the DEF manufacturers. My result
with the Leica was also backed up by the same measurements
on the identical model Reichart refractometer.
After all of this, my conclusion is that to be sure of DEF
quality using a hand-held tester, to use a DEF specific
refractometer that indicates % of urea, not a common battery
and coolant refractometer. Depending on how much one is
willing to spend, DEF hydrometers can be purchased in the
traditional float style hydrometer, analog refractometer as
used in this post, or digital.
I would like to test DEF using a dedicated float type DEF
hydrometer and if available, a refractometer specifically
identified for DEF measurement, because my suspicions are
that the battery electrolyte specific gravity range does not
provide sufficient accuracy when using a refractometer that
is not dedicated to testing the specific fluid.
I suspect that since the SG value achieved on the Leica was
so close to the original listed DEF specs in SI, that this
tool was possibly originally used to identify that value.
Just my opinions, based on the numbers achieved multiple
times using clean containers and test instruments. Looking
at combination refractometers that can be used for DEF,
coolant and battery electrolyte testing, each as its own
dedicated scale. Food for thought.
At the end of it all, even given any inaccuracies in the
measuring tool used, achieving the 1.295 value by the
service technician would support an excessive ratio of water
Martin from British Columbia