Want More
Engine Operating Info
Add a Pair
of Gauges
By:
Andy Wiedeman
Member of the Rocky Mountain A’s of
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Why Add Water Temperature
and Oil Pressure Gauges?
Types
of Water Temperature and Oil Pressure Gauges
How
to Interface to the Water Temperature Gauge
Introduction
The Model A as
delivered from the factory did not have any means of monitoring the operational
parameters of the engine as the car was being driven. The most common desired measurements desired in
the early days were water temperature and oil pressure. Many Model A owners during the production years, and afterward added
temperature and oil pressure gauges using aftermarket gauges and devices
manufactured by several companies.
Nothing much has changed, we all still want to
know “what’s going on in the engine?”
Many restorations, over the years, have included the addition of water
temperature and oil pressure gauges. This article is not intended to repeat the
details of what other authors have done.
Instead, we intend to show one installation, as an example of a typical
gauge installation using parts available from typical Model A
mail order catalog sources. Les Andrews
in his book The Model A Mechanic Vol. II has a section
on adding a water temperature gauge, however, does not cover the installation
of an oil pressure gauge.
Why Add Water Temperature and Oil Pressure Gauges?
In the 1930s and
today, many owners have simply added a “Moto-Meter”
which attaches to the radiator filler neck, and records the air temperature
above the water circulating in the upper tank of the radiator. However, particularly in
Many owners of
restored Model A Fords do not see the need for an oil
pressure gauge which indicates only that the pump is putting out about 3 psi. However, for “peace of mind”
and to make an “elegant” installation, I decided to add an oil pressure
gauge. Model A
owners in the 1930s recognized the need for an oil pressure gauge and many were
offered as after market accessories. To
show that there is “nothing new under the sun” , some manufacturers offered lights that flash, or turn on when the
pressure is low or gone, a forerunner of the “Idiot” lights of the 1960s and
1970s (aren’t we glad that fad is over!!!).
Today, many owners still wish to have this “peace of mind” and believe
that the addition of an oil pressure gauge is beneficial. Since the addition of the oil pressure gauge
was rather inexpensive, and I was going to have all the work to add a water
temperature gauge anyway, it seemed logical to add the oil pressure gauge at
the same time.
With regard to
authenticity, there were several types of gauges available in the 1930s as
aftermarket additions. Fortunately for
us, one of these gauge sets are still available which
are reproductions of the types used in the early years of the Model A. You can add a set of these gauges without
ruining the “look” of the old Model A.
Why Write this Article?
We seek to
expand on the information others have provided on this topic, and discuss one
way to add these gauges to your Model A. While this is not the only way to add
gauges, it does so using readily available parts, and provides some insight to
problems you may incur in the installation of the temperature gauge.
Types of Water Temperature and Oil Pressure Gauges
You can obtain
single temperature gauges and oil pressure gauges at most of the common auto
parts suppliers, either in town or on the Internet. These generally come with a mounting bracket
which you will need to modify to work with the Model A. Alternatively, the Model A
parts suppliers catalogs offer both reproduction Moto-Meters
and continuous monitoring gauges which are based on aftermarket designs
available during the production of the Model A and after. The aftermarket
reproductions of the Moto-Meter are quite good. The “Quail” aftermarket radiator ornament is
also offered with a type of measurement tool similar to the Moto-Meter. The aftermarket continuous monitoring
temperature gauges are generally reproductions of Rex-a-Co gauges offered in
1931 by the Rex Accessories Co. of Racine Wisconsin. These gauges today are manufactured by
Stewart Warner and are of high quality.
Water Temperature Gauges
There are two
ways to measure the water temperature in your Model A
engine. The first is easy. A Moto-Meter can be
added to the radiator neck which is visible through the windshield. This meter, does not measure the temperature
of the water, but instead samples the temperature of the air above the water
circulating in the upper radiator tank.
As such the Moto-Meter does not give an
accurate reading, or in some instances, any reading at all. Depending on the altitude and your driving
habits, the red indicator may not show in the “window” when the Model A is
operating normally. If the engine begins
to overheat, while climbing a long hill, or sitting in a parade without moving
much, the water in the radiator upper tank will flash into steam, causing the Moto-Meter to instantly show the red indicator in the
“window”. However, by this time it is
too late, and your car will be boiling, causing water and steam to emit from
the radiator filler neck.
The second
method provides an accurate measurement of the water itself. A probe is inserted into the water stream
being pumped from the engine head into the upper radiator tank. This probe provides a means to move a pointer
on a gauge which is installed in the passenger/driver compartment. Several means for mounting this gauge are
available. These gauges were available
in the 1930s. The use of this type of
gauge is recommended so that the owner can monitor the engine outlet water
temperature, and shut down the engine prior to severe overheating, with the
possibility of damaging an expensive engine.
The continuous
measuring water temperature gauge works on an old non-electric principle. The probe consists of a hollow spring
enclosed in a waterproof housing. The
probe and the tube leading from the tube into the passenger/driver compartment are
filled with alcohol under pressure. When
the probe is exposed to changing temperatures, the alcohol expands or
contracts, thus moving a small column of alcohol in the tube leading from the
probe to the gauge indicator. This
expansion in the tube causes the dial indicator to move. Calibration at the factory of the internal
probe spring and the dial at various pressures (temperatures) allows accurate measurement of the water temperature.
Oil Pressure Gauge
Many Model A owners today consider an oil pressure gauge to be an extra
cost nuisance and not necessary. Generally,
this thought comes from “Henry did not think it necessary” and
that “the oil pressure is so low why bother”.
While I understand this line of thinking, consider that a gauge will assure
you that some oil is indeed circulating in the system. The common practice in the 1930s was to add
an oil pressure gauge, if only for the “peace of mind” that you get from seeing
some indication on the gauge dial. Dykes
Motor Manual published in 1929 says “It is a good idea to have a gauge for the
following reasons. The gauge will
provide an indication of the range of oil pressure during driving. Too low a pressure at a normal speed can
indicate that the engine has run too long with the “choker” on. Too high a pressure will cause abnormal oil
consumption. A high reading can indicate
that the system has a blockage A fluctuating oil pressure indication
at a constant speed can indicate a need to add oil.”
There are two
types of oil flow indicators. The first,
not often seen, is called a “sight feed” gauge.
This type is generally mounted on the dash, and has an inlet and an outlet
pipe attached. The “sight feed” type
does not actually measure the pressure, but instead allows the driver to
visually inspect that there is oil flowing through a glass tube in the gauge.
The second type
is the more common oil pressure gauge.
This gauge operates on the principle of compressing air in a “Bourdon
Tube”. The Bourdon Tube is attached to a
long tube connected to the output of the oil pump. In the Model A oil
pressure accessory, this attachment is to a fitting in the block, directly
below the carburetor. The tube is routed
up and through the wiring terminal block, into the passenger/driver compartment
to the gauge. In operation, the oil at
low pressure will fill to about ¼ the length of the pipe leading to the gauge,
at high speeds, the oil will be about ¾ of the way up the pipe. This movement of oil,
compresses the air in the tube, and in a thin metal expanding tube in the gauge
itself. The greater the speed of the oil
pump (the engine) the greater the compression of the air. This compression causes the Bourdon tube to
straighten out operating a lever, which is calibrated to cause a pointer to
register the pressure in the output of the oil pump. The higher the engine RPM
the higher the pressure reading. What I have experienced is that when
the engine is cold, the pressure may be 10 psi or
even more pinning the meter. As the
engine warms up, this rapidly decreases to about 3 psi
at 1200 RPM to 6 psi at 2250 RPM. During idling conditions, with the engine
warm, the pressure is about
1.5 psi.
The oil pressure
gauge is easily installed on a Model A, and reproduction gauges provided in the
1930s are available. If you are going to
add a water temperature gauge, it makes sense to add an oil pressure gauge at
the same time.
Reproduction Gauges
There are good
reproductions of authentic Model A aftermarket
temperature measurement gauges available by mail-order and over the internet. While there were at least 5 manufacturers of
water and oil pressure gauges during the Model A manufacturing years and after,
there is only one now available. These
gauges are manufactured by Stewart Warner, and duplicate the design of the old
Rex Accessory Company’s combination Oil Gauge and Heat Indicator. The original Rex-A-Co gauges advertisement is
shown below.
The above at was
taken from a magazine in March 1931.
Alternatively,
if you are not so interested in reproduction parts, you can obtain both oil and
temperature gauges at most auto parts suppliers and adapt them to your car.
Mounting Options
I reviewed Les Andrews book on temperature gauge installation, and decided
that I wanted to both have a reproduction gauge, and that I wanted to have both
a temperature gauge and an oil pressure gauge.
I found that there are two mounting options. You can attach to gauges to the steering
column, either singly, or by using a bracket that puts one gauge on each side
of the steering column. There is also a
bracket which will allow you to mount a gauge under or on top of the steering
column. Alternatively, you can add
either a single gauge or a set of both oil pressure and water temperature
gauges directly below the current instrument cluster. In the 1930s the predominant method was to
add the gauges directly below the instrument cluster, although some owners
probably mounted them on the steering column.
I was interested
in authenticity so I chose reproduction gauges and to add the gauges directly
below the instrument cluster as was done in the early 1930s. If you have long legs you may also want to use
the under instrument cluster approach, due to limited mounting room under the
steering wheel. I found that my knees
would bang up against the instruments while driving.
The finished installation is shown below.
The installation
of the gauges was facilitated by the purchase of a bracket supplied by Bert’s
Model A Center.
There are two versions available that will hold two gauges. One is chrome plated, the other is
unpainted. I originally intended to get
the chrome plated version, but due to a slight mixup,
I ended up with the unpainted version.
After contemplating whether or not to send it back, I decided to paint
it black instead. Now, I am very happy
with the results. The visual appearance is great, and not to overwhelming, you
may want to consider this option prior to purchasing the bracket. Be sure to install the brackets, gauges etc.
before attaching the probe to the engine.
Several things
that I found I needed to do when installing the gauges in the driver/passenger
compartment. You need two longer screws
to attach the instrument cluster and the gauge bracket to the dash. I found suitable stainless steel screws at
Home Depot. If you decide on the black
(or some other color) bracket you will need to paint the sides of the gauges,
since they are quite visible from both outside and inside the car. Finally, the gauges are supplied with a light
in each one for viewing during night driving. The gauges come with 12V bulbs, therefore, if
you have a -6V system you need to change the bulbs to 6V. You can wire them in parallel with the
instrument cluster light and use the on/off switch in that device to turn on
and off the gauge lights. For more
information on control of the gauge lights see my article on accessory wiring
and control, elsewhere on this website.
A close up view
of the gauges and the mounting is shown in the photo below.
How to Interface to the Water Temperature Gauge
To install the temperature
gauge shown above you need a means of getting the temperature probe into the
water stream at the outlet of the engine.
Several means of doing this have been developed by others such as:
1)
Drill
and Tap the existing water outlet fitting to interface to the probe.
2)
Use
a specially made water outlet fitting with a fitting drilled and tapped
3)
Use
an aftermarket steel pipe which has a raised boss which is inserted in the
upper radiator hose.
Any of these
means can be used. The easiest and best
looking way is to purchase an aftermarket water outlet fitting. Bert’s Model A
Center will be getting these, but none are available now. The second easiest is to purchase the steel
tube, cut the upper radiator hose into two slightly shorter sections, and
insert the probe interface tube between these sections. Finally, if you have the right equipment, you
can remanufacture your own water outlet fitting to accept the probe. If you attempt this conversion, be sure to
weld a boss about ½ to ¾ inch long onto the outlet
fitting, before drilling and tapping.
This boss is to ensure that the water temperature probe is contacting
the water circulating from the engine to the radiator, but not blocking the water
outlet pipe. The probe is about ½ inch
in diameter, if it were inserted without the boss it
would go all the way into the pipe and would reduce the flow of the water from
the engine to the radiator causing overheating. In my case I used the aftermarket steel pipe
as shown below. The installation is not
as clean looking but it was quick and easy.
If you are more finicky about the look of the installation wait for the
Bert’s new water inlet pipe that has a boss already welded onto it and a hole
drilled and tapped to accept the probe. This method is not as “clean” looking as the
drilled and tapped water output fitting. A good picture of the modified water
outlet fitting with the boss and the probe is shown in Les Andrews
book. However, at the time of this
writing there are none of these currently available, and the aftermarket probe
interface tube is quick and easy.
Probe Installation
In the above
view you can clearly see the probe (brass color) screwed into the aftermarket
pipe. In Les Andrews
book, he shows the capillary tube (the tube filled with alcohol) being routed
above the engine, and near the spark plug wires and unsupported for the length
of the engine. This installation,
is to be avoided. It is possible that
the tube could come in contact with the spark plugs or the spark feed brass
conductors. While the tube is
constructed with an outer coating of polyurethane, it is also possible that
vibration could cause the polyurethane to be damaged and worn through, exposing
the inner metal tube, causing a short of high voltage to the probe and the
gauge. A better means is shown
above. Route the tube (it’s the black
cable/tube coming out of the probe) up and along one of the radiator support
rods. Secure the tube to the rod in
several places with electrical tape and/or a tie wrap.
Problems with Installation
No big problems
were incurred with the installation with the exception of inserting the
aftermarket probe interface tube into the upper radiator hose. The problem arose because I also purchased a
new set of radiator hoses from Vintque Inc. at the
same time. During the installation, I fit checked the
probe interface tube to the old radiator hose (Gates). It seemed to go in OK. When assembling the steel probe interface
tube to the NEW Vintique radiator hose I cut an approximate 1 inch
length of hose out of the middle of the radiator hose to accommodate the probe
(see the photo above). I then attempted
to pre assemble the probe interface tube to the two new sections of the upper
radiator hose. Arrrgggh, …. there was no way the probe interface tube would fit into the
NEW Vintique radiator hose. I tried everything, lubricating with various
oils, soaps and other stuff. I tried
trimming some of the inner material of the hoses to get a funnel shape. Arrrggggh … nothing worked. Then out came the dial calipers to measure
the parts. Here is what I found. The diameter of the aftermarket steel tube
had a swaged bulb on each end of the tube.
The diameter of this bulb was much larger than the inside diameter of
the Vintique radiator hose, causing the interference
condition.
The old plyable Gates hose would interface to the probe with some
difficulty, but the NEW hard and rigid Vintique hose
could not. The reason is that the larger
diameter of the steel tube causes a 0.145 inch of aftermarket probe tube OD
interference with the 2.015 inch diameter ID of the NEW Vintique
hose and prevented all attempts to assemble.
The aftermarket probe interface tube has swaged bulbs on each end. This causes the tube OD to be larger in
diameter than the body. The solution is
to cut off about 7/16 inch on each end of the interface tube eliminating the
bulbs.
By the way, NO
ONE mentions that this is a problem … probably many others have found this out AFTER
buying the parts, only to get frustrated and get out the hacksaw.
The results of the surgery are shown below.
After cutting
the aftermarket probe interface tube and lubricating the radiator hose it was
possible to pre-assemble the two sections of the Vintique
radiator hose to the steel probe interface pipe. After pre-assembly the hose/aftermarket probe
interface can be assembled between the water outlet fitting and the upper
radiator tank.