Red Flashing Coolant Light

[jms1075]

Hey all, I had an issue arise the other day that has me somewhat baffled. I was about 50 minutes into a drive (most of the way was highway but I was sitting in traffic when it happened). I heard a beep from the dash and assumed it was my gas light since I knew it was low, but much to my surprise it was my red coolant light and I noticed the coolant temp gauge was about 3/4 of the way up. I immediately pulled over and opened my hood. My coolant reservoir was just below the max line (where it usually is), so now I am thinking my thermostat is stuck shut. I let the car cool down, got back in turned it on and the low coolant light stayed on for about 10 more seconds then went off and the operating temp went back down to the the middle of the gauge and the problem has not happened again since.

I live in NC and it was about 88 and sunny when it happened, my question is, would my thermostat even shut once the car is up to operating temperature? I am thinking there is no reason it should be shutting if I just drove at 75mph for 45 minutes and then sitting in traffic I would think it would be staying open. Is there anything else that can cause the low coolant light to come on? I would think it would be the sensor, but with the coolant temp rising to 3/4 on the gauge I think there really was an issue with coolant getting to the engine.

I will add that I have always used g12 coolant in my car, and mixed with distilled water to no more than 50/50. A few days prior to this incident, I did drive through somewhat high water (maybe up to the bottom of the front bumper cover) is there anything that could have happened during that, that would have caused an issue? I figure the problem will come back at some point, issues like that usually don't just happen for no reason.

Any help would be appreciated. Also the car is a 2005 3.0 A4. The thermostat was replaced about 55.000 miles ago which has me skeptical about it being that as well.

[SJorge3442]

Hey all, I had an issue arise the other day that has me somewhat baffled. I was about 50 minutes into a drive (most of the way was highway but I was sitting in traffic when it happened). I heard a beep from the dash and assumed it was my gas light since I knew it was low, but much to my surprise it was my red coolant light and I noticed the coolant temp gauge was about 3/4 of the way up. I immediately pulled over and opened my hood. My coolant reservoir was just below the max line (where it usually is), so now I am thinking my thermostat is stuck shut. I let the car cool down, got back in turned it on and the low coolant light stayed on for about 10 more seconds then went off and the operating temp went back down to the the middle of the gauge and the problem has not happened again since.

I live in NC and it was about 88 and sunny when it happened, my question is, would my thermostat even shut once the car is up to operating temperature? I am thinking there is no reason it should be shutting if I just drove at 75mph for 45 minutes and then sitting in traffic I would think it would be staying open. Is there anything else that can cause the low coolant light to come on? I would think it would be the sensor, but with the coolant temp rising to 3/4 on the gauge I think there really was an issue with coolant getting to the engine.

I will add that I have always used g12 coolant in my car, and mixed with distilled water to no more than 50/50. A few days prior to this incident, I did drive through somewhat high water (maybe up to the bottom of the front bumper cover) is there anything that could have happened during that, that would have caused an issue? I figure the problem will come back at some point, issues like that usually don't just happen for no reason.

Any help would be appreciated. Also the car is a 2005 3.0 A4. The thermostat was replaced about 55.000 miles ago which has me skeptical about it being that as well.

Could be so many things. First thing that comes to mind is perhaps the coolant isn't actually high and its just a false positive. Do you have Torque and a bluetooth OBDII reader? Would be great to keep an eye on temps overtime to see whats going. Second thing that comes to mind is the pressure in the cooling system. Could be a leak, thus not allowing the system to operate under pressure, which causes the coolant to boil sooner. I'd log coolant temps and also pressure test the system to find out if the system has any leaks along the way.

[pablolizarraga]

When car gets to operating temp, check if the radiator fan turns on. And as mentioned, get car scanned for codes. If you don’t have OBDII, Autozone lends a scanner that may yield useful info.


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[jubei4769]

Flashing coolant light means low coolant. If the reservoir was still full and not low I’d check the wiring to the sensor or just get a new expansion tank.


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[Turbo510]

I noticed the coolant temp gauge was about 3/4 of the way up. I immediately pulled over and opened my hood. My coolant reservoir was just below the max line (where it usually is), so now I am thinking my thermostat is stuck shut. I let the car cool down, got back in turned it on and the low coolant light stayed on for about 10 more seconds then went off and the operating temp went back down to the the middle of the gauge and the problem has not happened again since.

Sounds like a sensor issue to me, especially because, as I understand it, when you re-started the engine, the coolant gauge and warning still showed a problem, then suddenly they went back to normal.

[SJorge3442]

Sounds like a sensor issue to me, especially because, as I understand it, when you re-started the engine, the coolant gauge and warning still showed a problem, then suddenly they went back to normal.

Thats where my mind was going too. Thats why I was saying to check the temps to see whats going on. Torque + ELM BT connector has to be one of the most used tools in my "tool box". Cant really say that since I have it all the time. I do have multiple adapters though so I can check other peoples issues too.

another +1 to Pablos rec's. Check to see that the fans are running.

[pablolizarraga]

Had a Jeep that would overheat because fan would sometimes not turn on when engine temp gauge started rising above middle. Opened hood and sure enough, fan was not on. I whacked it with a hammer and it turned on. It was soon replaced.


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[EuroxS4]

That coolant light will come on if you have a sensor unplugged or coolant resovior unplugged as well.check the wiring and plug.

[jms1075]

Hey all, I appreciate all the feedback. Today I had another issue arise that I am thinking can be related. So the same issue happened again, and again I pulled over for 10 minutes let it cool down and then the operating temp was normal. The difference this time is now my car was misfiring very bad. Stopped got codes read and got multiple random misfires and then codes for 4 of the 6 cylinders misfiring. Would a coolant temperature sensor cause all of the above issues? I'll go back later tonight and start it and see if it is still missing after it has a chance to get cold.

Thanks again

[customa4]

Starting to sound more like a head gasket issue.

[SJorge3442]

Starting to sound more like a head gasket issue.

Yeah. I'm thinking the same there. Cooling system isn't pressurized(causing temp to spike) and its leaking into the combustion chamber causing the misfires.

[Roadie73]

Found this thread today as I'm having a similar issue with my B6 (2003, 1.8T)...

It's happened a couple of times - 1st time was in stop/go bumper to bumper traffic - noticed the temp gauge had moved from the normal 90 to the next tick clockwise, and the coolant indicator was flashing. Pulled off the highway at the next exit, and once there was airflow back over the rad the temp dropped back to 90 and the flashing light disappeared.

The next time it happened was the same sort of situation - stop and go traffic. This time I had torque running and was watch the temps. From past experience, the temp (on torque) rises to about 100 deg before the thermostat / fans kick on - I've never seen it higher. But today it kept climbing - and once it crossed 110 (I think) the flashing coolant indicator came back. Turned the car around and an took a less congested way - as soon as there was air across the rad the temp dropped back down to the 93-98 range.

Coolant level is fine, and there are no other engine / drive-ability issues (eg poor idle / stuttering etc).

Went to check the fuse for the fan (slot 9? on the fuse panel). No fuse, but when I tried to install one I discovered that there are no contacts for one either :(

Looked under the hood and the fan connector appears seated (but will give it a tug later once everything's cooled down).

Any ideas / suggestions?