Coolant Cold/Hot Dash Light Red & Blinking

This happened last year also but it has come up again. Not sure if it was around colder Fall/Winter weather or not but maybe coolant plays tricks when it is cooler. Anyway, couple weeks ago the dash light that shows cold coolant (blue) and then normally
goes out when the 2001 TDI Beetle is warmed up went Red and blinking right after starting up the Beetle in the morning. Maybe 30 seconds after it started. Like I did last year, I added 1/2 cup, maybe a cup, of distilled water, and all was well. I would say my coolant is right in the middle seam of the bottle so higher than the side markers (that you can't see anyway the way the bottle is mounted). Couple weeks go by and the red light blinking came on again. I added a scotch more of distilled water, maybe 3/4 cup, and the light is back to normal blue in AM and then goes out. Again, water level at about 1/2 bottle as best I can tell.

So, is the sensor in these bottles that touchy? Any fixes for this. Obviously adding the little extra water seemed to do the trick so I am guessing the sensor in the bottle, if it has one, is at fault. I did unconnect the cable connector going to the bottle and re-connected. Not sure if that helped.

Thanks

tj

My 2004, when cold would set off the low coolant warning light. But only when cold (Below 45F). Then when warm, (after a restart) the light would go off. The dealer replaced the coolant tank and the problem went away. I think there is some problem with the sensor in the tank that only shows up when cold.

amishman said:

So, is the sensor in these bottles that touchy? Any fixes for this. Obviously adding the little extra water seemed to do the trick so I am guessing the sensor in the bottle, tj

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This is the most plausible description to date. I am still having this issue on my 05 Wagon. Is it possible that the coolant gets "thicker" at the top (or in the bottle) as cooler weather comes on... thereby loosing some conductivity? My light also goes out and all guages act normal once driven for 5-10 min... ie, once coolant has a chance to stir up. If the sensor was actually bad... wouldn't it still fault after driven? I don't mind spending the $$ on a new bottle, but hate the expenditure if not the real problem! I will try the addition of some distilled H2O, and post the results!

TNDiesel said:

I will try the addition of some distilled H2O, and post the results!

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Ok all, I added a slosh of distilled H2O to the expansion bottle before startup this morning (perfect weather conditions for error to occur based on previous observations 30 deg following a warm day before)... and voila... no blinking red light. Here is my theory... The coolant sensors use electrical conductivity of the coolant to sense its presence. I'm guessing that the coolant is less conductive than water and can be too strong in the mixture to allow the sensors to properly pick up the presence of coolant in the bottle... Can you see me jumping and leaping from hypothesis to conclusion? Any takers? it is working so far here. Others may want to try and see if this works!

The next question is why this would happen in the first place? Basically, my theory asserts that the coolant is becoming concentrated in the expansion bottle after shutdown.

Thoughts? opinions? scientific guesses?

Later,

Have had the same in my 03 Jetta TDI. As it was explained to me. When it gets a little cooler in the Fall, the G-12 contracts, and when the engine first starts up some is forced into the engine, or other wise taken out of the Expansion tank. Any good dealer would know to top off the expansion. I was having the oil changed when this was explained and demonstated.

The problem has not come back.

Uncle_Dave said:

Have had the same in my 03 Jetta TDI. As it was explained to me. When it gets a little cooler in the Fall, the G-12 contracts, and when the engine first starts up some is forced into the engine, or other wise taken out of the Expansion tank. .

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Hey all, there was another posting on this topic. I guess I posted my fix to the other discussion.

In my case the expansion tank was at the max level and the problem kept occuring. I ended up "cleaning" the coolant sensor prongs inside the expansion tank with a Q-tip. It seems some sort of invisable corrosion or scum had developed on the prongs reducing their ability to sense liquid (lessening conductivity) until the engine warmed up. I did this several weeks ago and the red light has NOT reoccured since!

All those with the flashing red light should try this quick fix. All it will cost is a Q-tip and some tape to attach it to an extender (long screw driver)!

TNDiesel said:

Hey all, there was another posting on this topic. I guess I posted my fix to the other discussion.

In my case the expansion tank was at the max level and the problem kept occuring. I ended up "cleaning" the coolant sensor prongs inside the expansion tank with a Q-tip. It seems some sort of invisable corrosion or scum had developed on the prongs reducing their ability to sense liquid (lessening conductivity) until the engine warmed up. I did this several weeks ago and the red light has NOT reoccured since!

All those with the flashing red light should try this quick fix. All it will cost is a Q-tip and some tape to attach it to an extender (long screw driver)!

Click to expand...

Did you do this with a full bottle of coolant or did you remove the bottle and have to refill coolant. I would like to try this but need a step by step if you can offer...

Thanks

tj

Low Coolant Sensor Fix!

amishman said:

Did you do this with a full bottle of coolant or did you remove the bottle and have to refill coolant. I would like to try this but need a step by step if you can offer...

Thanks

tj

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Amishman & others...

I just did this while the bottle was full and on the car. I used a screwdriver shaft with a Q-tip taped on the end. I attached the Q-tip with only the "puffed" end extending past the end to provide some strength. This allowed me to apply a little pressure to the prongs to clean them. Amazingly this worked after one simple 30 sec scrubbing. I have not had any little red coolant light flashing issues since.

I guess the prongs can accumulate some invisible corrosion lessening their ability to conduct current.

Let me know if you have any other questions. Please also post your results!

TNDiesel said:

Amishman & others...

I just did this while the bottle was full and on the car. I used a screwdriver shaft with a Q-tip taped on the end. I attached the Q-tip with only the "puffed" end extending past the end to provide some strength. This allowed me to apply a little pressure to the prongs to clean them. Amazingly this worked after one simple 30 sec scrubbing. I have not had any little red coolant light flashing issues since.

I guess the prongs can accumulate some invisible corrosion lessening their ability to conduct current.

Let me know if you have any other questions. Please also post your results!

Click to expand...

How deep are these prongs inside the bottle? Are they closer to the fender or inside of the engine side? I need to pop it pen and see but curious.

I have not had the light since adding the extra distilled water but I think I will remove a little coolant from the bottle as I am slightly above the middle seam of the bottle in coolant so it is above maximum amount recommended and I will try your trick.

Thanks

tj

tj

Sensor Prongs

amishman said:

How deep are these prongs inside the bottle? Are they closer to the fender or inside of the engine side? I need to pop it pen and see but curious.

tj

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The prongs extend above and below the centerline of the tank at an angle. I would say they are 3-4 inches down inside.

I hope this works for you as it did for me!