Kanto Seiki Fuel Gauge and Sending Unit

[desertrat]

Kanto Seiki Fuel Gauge and Sending Unit

An Introduction to a multipart post...

Two basic types of electric gauge systems were used in the Patrol. Electro-magnetic from the start of production until 1966 when the thermostatic type was phased in. To get a better understanding of the systems to aid in the troubleshooting, repair and replacement lets take a look at these gauge types and their origins.

The major 20th century names in automotive gauges were King-Seeley (Ford), AC (General Motors), Auto-Lite (Chrysler and later Ford) and others such as Stewart Warner, Smiths, VDO etc. Two basic types of electric gauges, electro-magnetic and thermostatic, with minor variations in design were used by these manufacturers. The variations in designs don’t lend the brands components to be inter-functional typically. The exception are the others who basically followed suit of Stewart Warner and are inter-functional.....mostly.

As typical of the age Japan did not reinvent the wheel often and to our benefit were experts at making knock-offs. Kanto Seiki who made the gauges for Nissan used the designs of Auto-Lite. Little info for the instruments is available in the service manuals and service bulletins from Nissan but enough is there that with some additional evidence we can conclusively link the designs to Auto-Lite. So let’s look to Auto-Lite to gleam some more insight to these gauge systems. Later we can add this understanding with the little factoids from the Nissan parts books and TSBs to build the picture of the instruments in the Patrol.

The spoiler alert to all this is that the Kanto Seiki gauges are inter-functional with a great many sending units available. But follow along if you want to know why.

[desertrat]

Most magnetic systems work on the same principles. The magnetic dash unit consists of two electromagnets that are opposite each other and placed in between is an armature with a needle attached to it. The tank unit consists of a rheostat with its value controlled by the float that follows the fuel.

In the Auto-Lite dash unit each electromagnet has its own winding fed in parallel to produce two distinct magnetic fields. One of the windings is grounded internally and provides constant magnetic pull toward “E”. The other winding has a variable field that is grounded through the tank unit. The variable field winding provides the pull to move the armature and pointer across the gauge to indicate fuel level.

The tank unit rheostat contains a resistor and a contact arm that move across the resistor in accordance with the position of the float. As the fuel level in the tank is increased and the float rises, the contact arm moves as to decrease the resistance in the circuit. This results in an increase in current flow, strengthening the magnetic field and moving the dash unit pointer proportionately higher. One thing to note is the system compensates for normal fluctuations in system voltage as the current in both legs remain in proportion to each other and thus the magnetic fields remain in proportion.

The Kanto Seiki magnetic system is the same as the Auto-Lite but…..just backwards.

See the below excerpt from the 1966 Patrol Service Bulletin.

image18.png

Kanto Seiki differences we are concerned with are 1) As the fuel level in the tank is decreased and the float drops, the contact arm moves as to DECREASE the resistance in the circuit. 2) The constant magnetic field pulls the dash unit needle to “F” and a DECREASE in tank unit resistance INCREASES the pull towards “E”. 3) The value of tank unit resistance that results in dash unit indications of “E”, “half” and “F” are INVERTED.

Next we’ll look at the “New Type” of gauge the Patrol had, the thermostatic or by-metal [sic] as referenced in the 1966 Nissan Patrol Service Bulletin.

[RiverPatrol]

Good stuff!

[desertrat]

Magnetic gauges are simple, voltage compensating, fast reaction and unaffected by temperature. But the magnetic leverage is only balanced at half scale and linearity is lost at each end of the scale. The fast reaction can appear as erratic needle movements following sloshing fuel and accurate fuel level can be difficult to determine.

Let’s take a look at how the Auto-Lite thermostatic system solves these problems at the cost of a bit more complexity.

The dash unit movement consists of a bimetallic strip wrapped in a variable winding of resistance wire that acts to heat the strip when current passes through the winding. The nature of two different metals with differing expansion rates bonded together into a strip, act to bend the strip as the metals change temperature. The bimetallic strip provides the pull to move the pointer across the gauge to indicate fuel level.

As the fuel level in the tank is increased and the float rises, the contact arm moves as to decrease the resistance in the circuit. This results in an increase in current flow, heating the bimetallic strip further and moving the dash unit pointer proportionately higher. Because of the time required to heat the bimetallic strip, the action of the thermostatic gauge is slow and the pointer will not change it’s position as result of sloshing fuel in the tank. But note the dash and tank unit are NOT voltage compensating.

The Kanto Seiki thermostatic system is the same as the Auto-Lite

See the below excerpt from the 1966 Patrol Service Bulletin.

image18-1.png

(Unfortunately the illustration contains a graphical error in the tank unit. But fortunately we can bench test the dash unit and tank unit and will prove to the contrary.)

Kanto Seiki similarities we are concerned with are 1) As the fuel level in the tank is decreased and the float drops, the contact arm moves as to INCREASE the resistance in the circuit. 2) The COLD bimetallic strip pulls the dash unit needle to “E” and a DECREASE in tank unit resistance HEATS the bimetallic strip to pull towards “F”. 3) The value of tank unit resistance that results in dash unit indications of “E”, “half” and “F” are IDENTICAL.

Next we’ll address supplying a constant voltage to the gauge to compensate for the systems lack of intrinsic voltage compensation.

[desertrat]

According to Ohm’s Law we know that the voltage divided by the resistance in Ohms equals the current. The variable voltage of the vehicle electrical system would result in a fluctuating current and dash unit needle without some sort of voltage regulation.

The Auto-Lite and Kanto Seiki regulator is an electro-mechanical device. A bimetallic strip is heated by a winding internally grounded. The bimetallic strip operates a set of electrical contacts that make or break the gauge circuit. Higher system voltage heats the strip faster and opens the contacts more often. Thus the regulator does not produce a steady DC voltage output, but, rather a pulsating voltage at an effective constant average 5.0 (8.0 Kanto Seiki) volts. The bimetallic strip compensates for ambient temperature and therefore should be mounted near the dash unit at the same ambient temperature and well grounded.

The voltage regulator in the Patrol was introduced with the thermostatic gauges in 1966 and was mounted on the inside of the firewall and fed both the temperature and fuel gauges. In late 1969 the regulator was incorporated into the temperature gauge of the cluster unit and fed the fuel gauge internally.
To recap on what we know so far of the Patrols gauge systems:

Beginning to 1966

Magnetic fuel gauge system*
• Gauge fed with full electrical system voltage
• Resistance to ground presented to tank unit terminal of dash unit
◦ High Ω resistance = Full scale indication
◦ Low Ω resistance = Empty scale indication

1966 - End of production

Thermostatic fuel gauge system (Often these are referred to as a Constant Voltage system)
• Gauge fed with 8.0V from voltage regulator
• Resistance to ground presented to tank unit terminal of dash unit
◦ High Ω resistance = Empty scale indication
◦ Low Ω resistance = Full scale indication

*(There is a discrepancy between the electrical schematic of the magnetic system in the Nissan literature and what you will probably actually find in the internals of the dash unit. As far as we’re concerned it doesn’t affect our basic understanding of the magnetic gauges.)

As it turns out we have gauges that will accept readily available tank unit senders. They may not be universally bolt-in ready but nonetheless the sending unit ohmic ranges are far from unique to the Patrol. Next we’ll take a look at how we can determine the correct ohmic scale of our gauge systems.

[RiverPatrol]

Well this explains why swapping gauges from various years is often frustrating when the gauges won't work properly. I recall L60Boerne having a situation where his fuel gauge read in reverse when he installed replacement gauges. I also wasn't aware the late '69 gauges incorporated the regulator internally. I think that would mean they should work in all earlier years, except pre '66 the fuel gauge will read in reverse.

Great stuff! I've made this a Sticky.

[desertrat]

Nissans test procedures for the magnetic gauges are limited and specs are non-existent. But with known good dash units and using ques from Auto-Lite, AC and others we can build our own specs with some simple tools. The 1977 Patrol service manual does give a mid scale spec for the thermostatic gauge and we can turn to other Nissan service manuals contemporary to the Patrol. Again we can verify these specs by testing a known good dash unit.

Gauges are typically calibrated for mid-scale accuracy. It seems engineers figure you know when your tank is full because you just filled it. If you’re on empty it’s too late anyhow, that’s why you carry a Jerry can. But a typical accuracy spec you will find is at a certain given ohmic value the needle is only expected to register within + or – one needle width of the graduation mark.

Using a 0-100 ohm rheostat and voltage source we can sweep the dash unit needle from stop to stop and across the graduations. Then we can measure the value of the rheostat at each graduation and determine the respective values.

Why not just use a tank unit as a test tool?

Well few if any used ones are good unless you’re lucky or have a new old stock unit for comparison. Also the tank units often have slightly more ohmic travel than the dash unit needs to read from “E” to “F”. This “over travel”, as it’s referred to, is intentional to account for manufacturing tolerance and the fact that most lever arm float units are not linear proportionate. The float arm swings on an arc and the position of the float at half full may not coincide with the numerical center of the ohmic range for the sender. The importance of being aware of this will become quite apparent when considering a modern sender, linear reed type for instance, as a replacement.

Take for example the thermostatic dash unit which reads “E” at 73Ω and “F” at 10Ω. If we measure a new swing arm sender we will probably find the range to be from 90~88Ω to 5~0Ω. So we might venture to say 45Ω would indicate “half scale” on the dash unit. But the Nissan specs for the dash unit are 35~32Ω “half full” and a test would confirm this. So if we are substituting a linear sending unit such as a reed style, 90Ω to 0Ω, we may find ourselves disappointed that our dash unit will indicate 3/8 tank when in reality its half full. This is also true for some of the universal swing arm sending units available. We need to select a tank unit with the proper 1) ohmic range 2) travel and 3) depth adjustment to achieve “half full” accuracy. From there the “E” and “F” positions should fall into place.

So which tank units will work with our Patrol gauge systems?

[Esteban]

Thanks for this excellent course on fuel sending units and gauges. A must read!

[desertrat]

First let’s look at the specs of the Patrol gauge systems.

Magnetic fuel gauge system specs
• Resistance to ground presented to tank unit terminal of dash unit
◦ 90~∞ Ω resistance = Full scale indication
◦ 0~10 Ω resistance = Empty scale indication
◦ 45 Ω = Half scale

This system appears to have been serviced by the following part #’s

• Dash unit 25035-58000
• Tank unit 17291-44001

GM (AC) introduced a 0 to 90 Ω sender in the mid 60’s and in recent years Nissan and Toyota appears to have as well. Universal senders in this range are commonly available and can be fitted to the Patrol fuel tank.

Thermostatic fuel gauge system
• Resistance to ground presented to tank unit terminal of dash unit
◦ 73~∞ Ω resistance = Empty scale indication
◦ 0~10 Ω resistance = Full scale indication
◦ 32~35 Ω resistance = Half scale

This system appears to have been serviced by the following part #’s

• Dash unit 24860-80000 (to 09/69)
• Dash unit 24860-46500 (from 10/68 on)
• Tank unit 17291-44002 (to 12/72)
• Tank unit 25060-46500 (01/73 on, bayonet retaining ring)

Ford and Chrysler have used a 73 to 10 Ω sender for a great many years. So did Nissan in their other vehicles contemporary to the Patrol. Likewise universal senders in this range are commonly available and can be fitted to the Patrol fuel tank. Additionally in 1973 the fuel tank in the Patrol was changed to accommodate the 25060-46500 sender that is also shared by the Nissan 710/140J passenger car. This sender is readily available aftermarket as a drop in replacement for the tanks with the bayonet retaining ring.

Lastly we'll look at the instrument voltage regulator.

[Blue_Unicorn]

How many volts was the fuel and temperature regulator?