1984 XV1000 Low Fuel Sensor Thermistor Ohm Value (Calgary Alberta Canada) (INFO.)

Have a question about fixing something on a Yamaha Virago XV1000? Post it here!

Moderators: ViragoJoe, choppin

Post Reply
ksaumure
Posts: 8
Joined: Sun Apr 04, 2021 12:48 pm
Location: Calgary Alberta Canada
What Virago you Own: 1984 Yamaha Virago 1000
Completely 100% stock and all original
Currently undergoing minor daily restoration
Contact:

1984 XV1000 Low Fuel Sensor Thermistor Ohm Value (Calgary Alberta Canada) (INFO.)

Post by ksaumure » Fri Aug 27, 2021 9:41 pm

I've looked at the only other post and this would apply to other Viragos with a low fuel light system.

My thermistor in the tank sender unit has failed. I can get the system to work (unplug the connection from the tank and couple the plug at the fuel pump control). This turns on my low fuel warning light (at the tach) and I hear the relays close to make the change to the fuel pumps, hence having to use the "RES" switch to turn the fuel pump back on. All that works - it's the thermistor in the sending unit that has failed and I do not want to simply buy a sending unit when I can get a thermistor for $2.

If I can get some help, I'd need someone with some technical knowledge to remove their seat, and find the fuel tank connection (two wire plug - should be black and green wires), unplug it and measure the resistance to the tank. It should be quite low - something in the 100ohm range regardless of how much fuel is in the tank.

Thanks
1984 Virago 1000
100% Stock and all original
Calgary, Alberta, Canada

ksaumure
Posts: 8
Joined: Sun Apr 04, 2021 12:48 pm
Location: Calgary Alberta Canada
What Virago you Own: 1984 Yamaha Virago 1000
Completely 100% stock and all original
Currently undergoing minor daily restoration
Contact:

Re: 1984 XV1000 Low Fuel Sensor Thermistor Ohm Value (Calgary Alberta Canada) (INFO.)

Post by ksaumure » Mon Aug 30, 2021 11:22 pm

Ended up with good resolve on this one. The thermistor in the low fuel circuit is definitely 1K ohm and 1/8watt judging by the size of it. Mine was, as expected, completely burned up. It is difficult to find a 1/8w 1K ohm axial thermistor but a 1/4 watt off the shelf thermistor will work - as mine did when I replaced it today. I purchased a 5 pack for about $2.50 CAD at a local electronics supply shop in Calgary, Canada.

https://www.be-electronics.com/product_p/02n102-1.htm

Just a quick note - there is a very quick way to test your low fuel light system. The obvious one is to first swap the low fuel lamp (behind the tach) out for a good one or test it with a meter. Second is to test the bike's circuit. You can test the thermistor very easily by simply unplugging the connection from the gas tank (seat removed) and measuring the resistance to the tank. It should be 1K at 20C or thereabouts. If it's cold, expect it to be a bit more, maybe 1500 ohms and less if it is hot out (that would show that your thermistor is working properly). An open or a short indicates a bad thermistor and they usually open due to the constant heat cycles. With a failed thermistor, the red fuel light will never come on and the fuel pump relay control will never turn the fuel pumps off - ergo your RES/ON switch is no longer in the circuit and does not function at all. Thanks a lot, Mr. Thermistor. Your only recourse for fuel remaining is the odometer as we all did in the old days.

To test the bike's circuit, with the same connector disconnected from the tank, you'll have to get a 1K ohm 1/4watt potentiometer from the electronics hobby store and simply connect it to the connector (2 wires). If you do this, make sure it is a linear and not a volume control type. Make sure the RES/ON switch is ON. Start with the pot at 1K and slowly adjust it to zero with it connected to the bike's circuit (tank side disconnected of course). The pot will behave as the thermistor would - slowly change resistance from 1K to around 15 ohms when at the least resistive point. The circuit (fuel pump relay control unit) will sense the lower resistance and around 200ohms, current will begin to flow and the red low fuel light will begin to illuminate. Continue bringing the pot (resistance) down and soon after reaching it's lowest resistance, a relay in the fuel pump control circuit should trip and turn the fuel pumps off. At that time, the RES/ON switch will have to be switched to RES in order to bring the fuel pump back online. A cheap and dirty way to do this test would be to simply short the connector, but I would advise against doing this for very long as you may cause too much current through the circuit and possibly causing damage to the fuel pump relay control unit.

There are also thermistor cans available on Amazon and at AliExpress - link below. These are direct and exact replacements to the Virago low fuel level sensors found in our bikes. All you need is a soldering iron, new gasket and some patience. Range in price is 10 to 25 dollars.

In the UK: https://spiyda.com/thermistor-sender-fo ... light.html

AliExpress: https://www.aliexpress.com/item/3279603 ... lJR0l&mp=1

Amazon Canada:

So if you want a functioning low fuel light system and you have money, buy the complete assembly on EBay or CMSNL for who knows...up to $150. Takes about 30 minutes to change out.

Second option is buy a low fuel thermistor can and simply solder it in. Again about 2 hours worth of work and $20.

Third option is do what I did and buy a $3 thermistor and do it all yourself. You'll have to tear the little brass can apart and do a lot of soldering taking care not to overheat the little 1/4 watt thermistor when you do. My entire episode cost me about 3 hours of my life. Anything other than a 1K thermistor will not work.

In all cases, be prepared to have a new gasket on hand and don't forget, you're dealing with fuel, heat and electricity. Be careful.
1984 Virago 1000
100% Stock and all original
Calgary, Alberta, Canada

User avatar
ViragoJoe
Moderator
Moderator
Posts: 2672
Joined: Wed May 20, 2015 10:36 am
Location: S.E. Michigan, USA
What Virago you Own: 1996 Virago Special XV1100SH

Re: 1984 XV1000 Low Fuel Sensor Thermistor Ohm Value (Calgary Alberta Canada) (INFO.)

Post by ViragoJoe » Tue Aug 31, 2021 5:47 am


Ken,
(ksaumure),

Good information my friend.

Thanks so much for posting.

I know, this will be great information for some folks.


I've attached a picture of the Thermister, so others will know what is being discussed here:

Click Image of Thermister to Enlarge:
THERMISTOR.jpg
You do not have the required permissions to view the files attached to this post.
ViragoJoe 🇺🇸
1996 XV1100SH Virago Special
"Never ride faster than your Guardian Angel can fly!!"
;)


NOTE TO ALL:
:arrow: Please edit your profile to include your location & Bike Information.
It will aid us in assisting you!

Post Reply