I would think that the varnish would actually make the light stay on more, being that it would act as extra thermal insulation. There are no contact that can be cleaned. It is just a wire with a thermally varied resistor soldered onto it. It is great that it worked for you however I would suggest that others just replace the thermistor if they are going to pull the fuel pump out. The contact cleaner does work on other cars with lights and fuel level sensors and Vince too I guess.

I am going to post my how to once I get a program to compress the pic sizes.

 

I know this is an Old thread.. But i always wanted to know why My Low fuel light wont work.
Sure the bulb works because the low fuel light comes on when the key is on before i start the car..
But when the fuel gets low. Wont work... I know nothing on this subject. i will look threw this more to see what i can find. i know there is alot to look through

 

My light still works. We are suppose to have below freezing temperatures tonight and I have my car parked on an incline with the passenger side down so I can see if the light will come on when the air temp is in the 30's. The only other test for this spec of thermistor is to make sure the light does not come on when it is 100 degrees and is submerged in fuel. I suppose some of the below zero people may need to perform this repair with the thermistor listed to see if it works all the way that cold. I live in SC so the cold is not that much of a problem for me. I think it will all work though.



Freak, If you read the thread you will find out how it works and how to fix it. You should have read the thread before you posted. People will think little of you for either posting without reading or they will just think it was way over your head and you failed to understand. It is also not an old thread since you did not post much later after the previous post. I have been working on fixing this for 2 years.

 

My light has started to glow a tiny bit with a full tank and the warmer weather. I believe this is an indicator that when it really warms up that the light is going to be more visible. I can tell that the fuel takes a long time to change temp do to all the mass. I need to recalculate the thermistor and try another one.

 

I installed the thermistor that was 1500 ohms instead of 1,000 ohms with the same B=3700. The light stopped glowing dimly with gas during hot evenings after warming all day and it still comes on when the gas gets low. No winter test until next winter.

 

It is 30 degrees outside and it takes the light 4 minutes to come on from a cold start and having sat for over 4 hours. What I think I have noticed is that the fuel level needs to be lower in the colder weather because any splashing of the fuel on the sensor or housing will cool it down and it needs several minutes without splashing to warm up. I think the housing for the sensor also conducts a good deal of heat out of the sensor when it touches that cold fuel. I did notice the sensor come on at higher levels after a long drive. This would be due to the fuel pump heating fuel that is sent to the injection system and then returned by the fuel pressure regulator. After enough of this cycling there will be a measurable increase in the fuel temperature and gas tank air temperature. I think this also brought on some of the dim glow I was having with the 1,000 ohm thermistor during April evenings.

Is all this behavior similar to a functioning stock sensor?

I am happy enough with the results considering the design and would suggest the 1,500 ohm B=3700 thermistor to others. I will update if anything else arises and write up a DIY once I get the pics hosted.

 

GOD...........BLESS..........VINCE!!!!!!

Contact cleaner solved my disappeared low fuel light!!!!

Before ordering a new thermistor capsule and desoldering/soldering it try the "Vince Easy Fix Trick": contact cleaner inside small tiny holes of thermistor capsule and also on pump assembly connectors. It you are lucky the sensor should resurrect!

 

What year is your car? If the earlier cars have a sensor that works by float switch, we should figure out what year the change was made. My car was a 1991 convertible.

 

My car Is 1991 too (registered in 91' but 1990 Model Year)

It s an european Rx7 FC Convertibile S5 Turbo 200Hp

 

Since this thread was already resurrected, I figure I would throw my hat in the ring guilt free....
Houpty, you mentioned that the low fuel light was just a 'dim glow' in warmer weather? They may have changed something from s4 to s5, but this makes me think that Aaron cake's comment on "It's not a thermistor" has merit. On my 86 base model, when I first got it, the light worked. What happened was, when it was "kinda low" the light would sort of slowly pulse/swell. It would go from off, gradually increase to full brightness, and then decrease back to off over the course of about 3 or 4 seconds, if memory serves. Then, once the tank hit "very low" it would be solid on. Somewhere along the way it broke, and now its just on 100% of the time, but I would love to get it working again if possible. Is what I described how it works for your thermistor fix? or is it more of an increase in brightness as the tank get lower and lower? Also, did you try any other thermistors that worked out better for you, in all weather?

Edit: But now you got me second guessing myself. Am I just crazy? misremembering? maybe it never did that at all, and it was just an increasing glow as the tank emptied... Does anyone at all anymore still have a working stock low fuel light?

 

I HAD TO REPEAT THE TREATMENT TODAY: the low fuel light went again!

But this time i used an "heavy" CRC Electro Cleaner. It's more powerful compared to the one i used before. Now the light works again!
I suspect, rather i'm sure, that with a mild "de-oxidation cleaning" of the low fuel light thermistor it can't clean all the mostuire and dirty from the contacts inside the capsule so it will form again brefly stopping the light again!

I hope that now it will last longer (many many years).

 

I read your post just now sorry for the late answer!

The light has a dimming behaviour you mentioned because it's a thermistor! When spurts of fuel hit the capsule when the car is moving the thermistor cool down again and the light is pulsing mild! That is enhanced if the contacts inside the capsule are partially oxidated when the fuel level lap the capsule. When the fuel level is very low and far from the thermistor capsule the light should be steady bright......if there is no oxidation on the contacts......otherwise it will be a mild light.....and it will gone soon because the contacts will be more dirty..