Using A Hydrometer; Hydrometer Temperature Correction - Cushman SHUTTLE 4X Technician's Repair And Service Manual

Read all of Section B and this section before attempting any procedure. Pay particular attention to Notices, Cautions, Warnings and Dangers.
.
Do not perform a hydrometer test on a battery that has just
been watered. The battery must go through at least one
charge and discharge cycle in order to permit the water to ade-
quately mix with the electrolyte.
The temperature of the electrolyte is important since
the hydrometer reading must be corrected to 80° F (27°
C). High quality hydrometers are equipped with an inter-
nal thermometer that will measure the temperature of
the electrolyte and will include a conversion scale to cor-
rect the float reading. It is important to recognize that the
electrolyte temperature is significantly different from the
ambient temperature if the vehicle has been operated.

Using A Hydrometer

1. Draw electrolyte into the hydrometer several times to
permit the thermometer to adjust to the electrolyte
temperature and note the reading. Examine the color
of the electrolyte. A brown or gray coloration indicates
a problem with the battery and is a sign that the bat-
tery is nearing the end of its life.
2. Draw the minimum quantity of electrolyte into the
hydrometer to permit the float to float freely without
contacting the top or bottom of the cylinder.
3. Hold the hydrometer in a vertical position at eye level
and note the reading where the electrolyte meets the
scale on the float.
4. Add or subtract four points (.004) to the reading for
every 10° F (6° C) the electrolyte temperature is
above or below 80° F (27° C). Adjust the reading to
conform with the electrolyte temperature, e.g., if the
reading indicates a specific gravity of 1.250 and the
electrolyte temperature is 90° F (32° C), add four
points (.004) to the 1.250 which gives a corrected
reading of 1.254. Similarly if the temperature was 70°
F (21° C), subtract four points (.004) from the 1.250
to give a corrected reading of 1.246 (Ref. Fig. 8 on
Page H-7).
5. Test each cell and note the readings (corrected to 80°
F or 27° C). A variation of fifty points between any two
cell readings (example 1.250 - 1.200) indicates a
problem with the low reading cell(s).
As a battery ages the specific gravity of the electrolyte
will decrease at full charge. This is not a reason to
replace the battery, providing all cells are within fifty
points of each other.
Since the hydrometer test is in response to a vehicle
exhibiting a performance problem, the vehicle should be
recharged and the test repeated. If the results indicate a
BATTERIES AND CHARGING
weak cell, the battery or batteries should be removed
and replaced with a good battery of the same brand,
type and approximate age.
Electrolyte
Temperature
° F
160
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
Fig. 8 Hydrometer Temperature Correction
Repair and Service Manual
° C
71.1 +.032
+.030
65.6 +.028
+.026
60.0 +.024
EXAMPLE #1:
+.022
Electrolyte Temperature
54.4 +.020
Above 80°F (27°C)
+.018
48,9 +.016
Electrolyte temperature
+.014
90° F (32° C)
43.3 +.012
Hydrometer reading 1.250
+.010
1.250 + .004 = 1.254
37.8 +.008
corrected specific gravity
+.006
32.2 +.004
+.002
26.7 0
–.002
21.1 –.004
–.006
EXAMPLE #2:
15.6 –.008
Electrolyte Temperature
–.010 Below 80°F (27 °C)
10 –.012
–.014
Electrolyte temperature
4.4 –.016
70° F (21° C)
–.018
Hydrometer reading 1.250
–1.1 –.020
1.250 - .004 = 1.246
–.022
corrected specific gravity
–6.7 –.024
–.026
–12.12 –.028
B
Page H-7