Flashing Coolant Light

[wewantutopia]

Ok I'm perplexed. For what problems does the coolant light flash for?

Friday Night I drove from Chicago to Steven's Point Wisconson. About 3/4 into the trip my light started flashing. Of course I pulled off the interstate right away to investigate. The engine wasn't steaming, didn't seem any hotter than usual for driving for 2.5 hours. Opened the coolant resivoir *slowly* of course it was hot and pressurized but it wasn't low. All seemed well so I got back on the highway watching everything VERY carefully. My gauge seems to be working as does my water pump and thermostat. When I would go up a hill, I would watch my gauge go up slightly then as the road leveled out my temp gauge went back down so I figure my thermo opened, cooled, and all was good. I am also running on veg. oil. so of course I turned off all electric heaters figuring they may have been contributing. Now the veg was only being heated with coolant heat. My veg tank is in my trunk with a coolant lines running to the trunk to heat the heat exchanger and I have an inline digital fuel temp gauge. I figured with the the fuel being heated by the coolant I could use the fuel temp to help watch engine temp. The fuel for the next 45 mins or so never varied from ~160*. I figured if the water pump wasn't working that the temp of the fuel would have gone down slowly since hot coolant would no longer have been heating it; this wasn't the case. I also was thinking that the temp guage may not have been working and my car could have really been overheating. If that was the case, I figured the fuel temp would have gone up significanly wich also didn't happen. (plus the coolant temp gauge responded properly going up and down hills). I got to my destination with no problem. Yesterday morning I checked the coolant, level was fine. I drove it later and no idiot light. I started even later to drive back to Chicago and the light wouldn't stop blinking again! It blinked the whole way home and I made it no problem. The car seems to be acting the same as it always does sans the idiot light. What could be the cause, the coolant temp sensor maybe?? Please Help!!

[Jake_Speed]

The coolant resevoir has a sensor/switch which signals low coolant and gives a blinking light. It is set to come on right around the min mark, so if you're a close to "min" any side to side movement of the car will make it come on... for example on a exit ramp. Try adding some coolant!

Jake

[Op-Ivy]

Double check your level while cold and running.

A little while ago one of my coolant hoses burst open. Fortunately it was in my driveway as I was letting it warm up. I was about to drive away when I saw the coolant light blinking. I got out and looked under my car and there was a nice puddle of coolant under...

I would check your level again making sure that it is right up to the max. The sensor may be faulty as well, but I suspect your level is just low.

[wewantutopia]

Coolant is at the Max Level. Thanks for the responses!

[Vincent Waldon]

The contacts can also get dirty, covered in sludge, etc, and trigger intermittently. On my 86 the sensor is encased in black plastic at the top of the overflow bottle ... if you use a pair of water pump pliers you can unscrew the sensor and have a look... it's just two stainless steel probes that stick down into the coolant.

Because it's at the top of the bottle the wires come out of the connector at a steep angle... I've had them break twice... worth a look. The connectors for for the throttle switches on the injector pump which trigger the upshift light are exactly the same... since I stripped the upshift light off years ago I now have two spare coolant sensor connectors !!

One other point... the warning light is latched... which means once it trips it will stay flashing until you shut off the ignition and restart. So, it's pretty easy for it to trip on an offramp or sharp corner if the level is iffy... you then pull over and everything looks fine.

[tylernt]

I agree with Jake_Speed, that's the most likely explanation. It appears that the same sender is used for both the gauge and the light, so if the gauge reads normal, it's probably the coolant level sender.

[coke]

On my 1990 Jetta, I had to short the contacts out with a paper clip because some idiot put brake fluid in the antifreeze reservoir and it screwed with the level sender. My light would come on when the coolant level was perfectly normal, so shorting it out with the paper clip fixed it for me.

[Fatmobile]

Try the resevoir sensor plug, turning it 180 and plug it back in.
It appears the sensor is not purely resistive, there might be caps and diodes in there so the plug needs to be plugged in the right way.
Edit:
OK it can be plugged in either way, I think it has a capacitor so the light will come on for awhile when you turn the ignition on.
Unplugging the sensor for the coolant temp gauge will reset it, if all the connections are good it should stay off.
The ground connection from the coolant level sensor needs to be good too, or it will see it as an open circuit.
The rubber cover pulls back away from the plug so you can measure voltage drop across the level sensor while running.
Cold it should be around 3 volts, warm it's closer to 5.5 volts.

[wewantutopia]

Thanks for all the replies. I unplugged it and plugged it back in the same way a few days ago. That was all I did; coolant level was fine. It hasn't blinked since (except when the vehicle starts for a few seconds like its supposed to) and I've driven a few hundred more miles. Crazy old cars!

[Fatmobile]

I know some of my problems came from a bad connection on the old sensor connectors.
It has sat in my garage for years.
So,... when you unplugged it and plugged it back in,... was it cold?... or was the engine coolant hot?

[wewantutopia]

Cold

[Fatmobile]

Riiiiight, that's the same as unplugging the coolant temp sensor... makes it think it's cold.
Temp sensor and level sensor are on the same circuit, working the same op amp inputs so they work together.
I built a circuit that will bolt to the back of a Rabbit instrument cluster, basically the same as the later stock coolant level warning light circuit. The op amp inputs change when the engine is hot... and the light is meant to latch on when the coolant circuit is unplugged and plugged back in... or the coolant is low enough to just splash on the sensor.
Unplugging the level sensor, then plugging it back in when the coolant is hot didn't shut the light off... but waiting until it cooled or pulling the coolant temp sensor when the engine is hot made my light go out,... if the coolant was high enough and all the coolant level connections were good.
Edit: My circuit probably isn't working like it should, if I turn the car off when it's warmed up, then start the car up the light stays on... until I disconnect the temp sender. It's probably not supposed to do that. I'll need to play with the circuit some more to figure it out.

[hagar]

ok coke --please --send me a JPEG of that little cutie in the Pink ---ballgown.

hagar.