Glow Plugs, Wilson Switch, Superglow How-To

Joined
Aug 30, 2010
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This is how I improved upon the stock Glow Plug System in my 70 Series Landcruiser.
I was finding the stock glow plug system wasn't warming the glow plugs long enough during cold weather.

First I dismantled a Battery Voltage Readout LCD I bought from Princess Auto (Schumacher Brand) and it replaced my now extinct adjustable suspension button:
Glow-Plug-Mod-1.jpg

Glow-Plug-Mod-2.jpg


Now I can see in real time, all the time what my battery is doing, and I can tell what the glow plugs are doing based on the voltage readout.
Some gents have recommended a light that is in parallel with the glow plugs.
This is also a good way of knowing if your glow plugs are working properly but a voltage readout offers more information on your entire system.

After that I ran a #16 AWG sized wire from No.1 Glow plug relay to one side of my momentary push button ( I actually pushed 5 spare wires through the firewall for future mods)
I use wire loom for all my cabling, it is cheap and offers extra protection against abrasion from vibration:

Cut into the glow plug light and momentary pushbutton:

Glow-Plug-Mod-4.jpg



Glow-Plug-Mod-5.jpg


Glow-Plug-Mod-6.jpg




Glow-Plug-Mod-7.jpg





Glow-Plug-Mod-12.jpg


Glow-Plug-Mod-8.jpg


By wiring it this way, the current Toyota "Superglow" system is intact and it is safer to operate the momentary push button because all the glow plug current doesn't have to go through the switch.
Also, using the existing No.1 relay, the switch can only be operated with the key in the "On" or "Start" position.
You don't want children or curious friends able to energize the glow plugs without the key in the ignition. Kids love to push buttons!

If you will be using this method to override your glow plugs, it's important that the rating of your glow plugs is above 10VDC operation.
You can prematurely burn out your glow plugs if excessively glowing the OEM 6VDC rated glow plugs.

Test for correct operation:

Glow-Plug-Mod-9.jpg



When you first turn your key to "ON", the Toyota Glow timer will energize No.1 Glow Relay which sends 12VDC across the glow plugs.
This provides maximum Wattage (Heat). This will typically be on for about 3 to 4 seconds before the timer disable No.1 Glow Relay.

After No.1 Glow Relay de-energizes, No.2 Glow Relay will energize. No.2 Glow Relay will provide 6VDC across the glow plugs for a much longer amount of time.
6VDC across the glow plugs will generate 1/4 of the Watts (ohms law).
Eventually the timer de-energizes No.2 glow relay and the engine will be running nice and warm.

Glow-Plug-Mod-11.jpg


During this entire process you can use the momentary pushbutton you installed to place 12VDC across the glow plugs longer than the Toyota Timer does.
If it is cold outside and superglow is only activated by the Toyota timer for 3-4 seconds, use your momentary switch to superglow for a bit longer.
It is recommended to superglow in durations of 5 second on-off intervals. Pushbutton for 5 seconds, then off, again for another 5 seconds and attempt starting engine.
If the engine starts, give the momentary button an additional superglow if the engine is sputtering until it runs smooth.
Be conservative with your pushbutton. 15 seconds should be the maximum time under the coldest conditions that you should be pushing it in.
You may drain your battery or prematurely wear out your glow plugs.

Here is a diagram I put together based on my own troubleshooting experience:

Glow-Plug-System-LJ78.jpg



Sequence of operation review:

  1. Water Temperature Sensor (thermistor) tells Pre-Heating Timer how long to run No.1 and No.2 glow plugs.
  2. Key to "ON" : No.1 Relay sends 12VDC to glow plugs giving it initial "Superglow" for a short period. (Around 3-5 seconds)
  3. Pre-Heating Timer shuts off No.1 Relay and energizes No.2 Relay.
  4. No.2 relay runs glow plugs at 6VDC to aid in the start up and continue warming up the engine. (Runs for a while depending on Water Temp. Sensor).
  5. After everything is satisfied the Timer shuts off all Voltage to the glow plugs.
  6. When you push the momentary switch, you are basically running the "Superglow" No.1 Relay longer than what the Pre-Heating Timer determined.
Looking at the graphs I would say that over the course of 20+ years, the Resistor, Current sensor, Pre-Heating Timer, or Water Temp. Sensor lose their accuracy in timing correctly.
The graphs show what the timer aims for in timing depending on temperatures. It seems Super glowing (12VDC) a few more seconds than the OEM timer improves start up of the vehicle.

So in theory 12VDC on a 11VDC rated glow plug will produce approx. 500 Watts.
When the timer drops to 6VDC (after only 3 seconds) only 1/4 the Wattage will be produced (ohms law).
So say that two glow plugs are dead, you will get only 250 Watts for the first three seconds (Superglow 12VDC), and then a mere 62.5 Watts for the remainder (Afterglow 6VDC).

So I guess a combination of a shortened glowing period and 1 or 2 dead plugs can lead to a pretty cold engine start!

Cheers!
 
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Joined
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...........So in theory 12VDC on a 11VDC rated glow plug will produce approx. 500 Watts.
When the timer drops to 6VDC (after only 3 seconds) only 1/4 the Wattage will be produced (ohms law)..............

Nice write-up Mark and I love your digital battery readout. That's such a nice touch.

Also it is good that you recommend using higher-voltage plugs because by doing that you greatly reduce the chances of burning them out (whenever you use your added momentary switch to reapply full-voltage to them).

However, I believe that by moving away from the OEM-spec 6V plugs you've effectively eliminated your second-stage glow plug operation altogether. (I think it is flawed to say that the wattage simply drops to 1/4 of what it was because that statement assumes the plug "hot-resistances" will be the same "under 6V" as they were "under 12V".) In other words, I believe those higher-voltage plugs will produce almost-zero watts in the second stage.

So on this basis, I think you should dump your No.2 relay, dropping resistor, coolant temperature sensor, etc ... so you end up with "just the first stage" which you can then apply as desired.

My 2 cents.

:beer:
 
Joined
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Messages
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However, I believe that by moving away from the OEM-spec 6V plugs you've effectively eliminated your second-stage glow plug operation altogether. (I think it is flawed to say that the wattage simply drops to 1/4 of what it was because that statement assumes the plug "hot-resistances" will be the same "under 6V" as they were "under 12V".) In other words, I believe those higher-voltage plugs will produce almost-zero watts in the second stage.

So on this basis, I think you should dump your No.2 relay, dropping resistor, coolant temperature sensor, etc ... so you end up with "just the first stage" which you can then apply as desired.

:beer:

Thanks for adding to this Lost Marbles. Your right about the resistance fluctuating. It's hard to get any factual numbers as far as wattage goes because as you say the plugs resistance will fluctuate as they get warmer and the current starts tapering off. Also depends on the wear and tear and the amount of carbon deposits on them and such. The 1/4 wattage is only in theory but I used it for an example to explain what's happening in the system.

Also correct about the No.2 glow plugs effectiveness diminishing once the plugs are upgraded to 10VDC or higher.
They will probably in fact be producing approx. 10% wattage from No.2 relay which is why more usage of the manual button is required now.
But there is no harm in leaving No.2 in there because the pushing of the manual button overrides the No.2 plugs entirely anyways.

I chose my method for the least intrusive and safest approach to adding the manual switch to the existing sytem. And when it comes time to sell the truck the, I don't want the next owner scratching their head wondering why all the components are missing. :censor:

Oh man you should have seen the Viper Security system installation I had to clean up from the previous owner underneath the steering column! :doh:

:cheers:
 
Joined
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Messages
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.........

But there is no harm in leaving No.2 in there because the pushing of the manual button overrides the No.2 plugs entirely anyways.

I chose my method for the least intrusive and safest approach to adding the manual switch to the existing sytem. And when it comes time to sell the truck the, I don't want the next owner scratching their head wondering why all the components are missing. .....

Good points Mark.

I have considered simplifying my BJ40's glow system and installing a momentary switch independant of my key-switch ... but my desire to keep things as close as possible to OEM is what's stopped me thus far.

:beer:
 

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