Lighting and coolant warning problems!

[gins beetle]

Hi all!

We have a 2000 beetle and occassionaly the blue low coolant temp light comes on (apart from the usual warm up period at startup) even when the car has been running for some time and in mild outside temperatures.

The other "strange happening" is that when idling and cold when the headlights are on, the lights "Dim" for a second or so every 20 or so seconds.

I have measured the voltage when this is happening and there is a distinct drop in voltage as if the alternator drops charging every now and then.

Anyone know why these things are happening??? The dealers are no help at all.

Thanks, Mark.

[Porkchop]

The coolant temp sensor is probably bad which is why you get the blue light randomly. It is to the right of the head - where the upper radiator hose comes into the "heart valve". It's like a $6 part and is easy to replace (just be sure to do it with the car bone cold... like after sitting overnight).

No idea on the dimming... sorry.

[gins beetle]

Thanks Porkchop.

I'll try a new sensor.

Mark.

[grde]

Our NB also experiences this issue of the lights dimming.

My best guess is that the voltage regulator on the back of the alternator is defective.

The part is about $75, but removing the alternator is a pain, so I haven't gotten around to it just yet.

I have noticed that ours doesn't have this problem when the radio and air conditioning are not in use.

[v132z]

I have similar problem with the coolant temp light. But instead of the solid light,I am getting a flashing bule light. And one time, the tachometer went over 3000 even when the car was in idle!! Any ideas what it might be?

[pmkg]

Check and see if your radiator cooling fans are cycling on and off. I had the problem right after doing the timing belt and water pump. I checked everything all connectors. I think I had a air bubble in the radiator causing the problem. Does your a/c work? Mine didn't work when the fans would cycle on and off. My lights would also dim. The reason I think it was an air bubble is because the problem fixed it's self. Just a little info.

[kcfoxie]

the dimming seems to be a known problem that most drivers have just gotten used to. It's not caused any significant problems that I can reall (please, someone, correct me if I am wrong here).

The temp sensor in my 02 finally failed and gave a check engine around 53,000 --- i never noticed the temp light but did notice the fan would stay on like a half hour after the car was shut off (and driven no more than 15 minutes in the city at a max speed of 50Mph).

[Porkchop]

Originally Posted by v132z

I have similar problem with the coolant temp light. But instead of the solid light,I am getting a flashing bule light. And one time, the tachometer went over 3000 even when the car was in idle!! Any ideas what it might be?

According to Bentley, flashing blue means electrical malfunction (cooling system related). Mine was fixed with aforementioned coolant sensor replacement.

I haven't had any tach gremlins (yet).

[v132z]

Originally Posted by Porkchop

According to Bentley, flashing blue means electrical malfunction (cooling system related). Mine was fixed with aforementioned coolant sensor replacement.

I haven't had any tach gremlins (yet).

I brought my car back to dealership this morning. They replaced the coolant temp sensor for me. All problems fixed.

[Benny Beetle]

It took me awhile to find this thread. I'm glad (I guess) to see I'm not the only one. My blue temp comes on (no flashing) after 6 miles or more of highway driving (then goes off again, eventually). So I guess it's back to the shop..... again!

[John Koch]

Originally Posted by gins beetle

Hi all!

We have a 2000 beetle and occassionaly the blue low coolant temp light comes on (apart from the usual warm up period at startup) even when the car has been running for some time and in mild outside temperatures.

The other "strange happening" is that when idling and cold when the headlights are on, the lights "Dim" for a second or so every 20 or so seconds.

I have measured the voltage when this is happening and there is a distinct drop in voltage as if the alternator drops charging every now and then.

Anyone know why these things are happening??? The dealers are no help at all.

Thanks, Mark.

I expect that these two conditions are not related. The blue temp. light on when engine is warmed, may indicate a bad coolant temp. sensor. Easy and cheap to replace. It also may indicate a short in this circuit. A VW scan can isolate the problem to a sensor or a short.
Lights dimming,ect is easily solved. VW's come with batteries barely large enough to support the normal load in moderate temps. In colder temps, a battery holds less of a charge for a shorter period of time. Thats why they are rated by cold cranking amps. A "load Test" done on the stock battery will tell you if the battery is still good. It can be done at any battery dealer. A VW stock battery with 70 amp hours and 340 cold cranking amps, when a load current of 200 is applied for 15 seconds, voltage should drop to 9.5 volts. Less than that means a partially charged battery. Voltage should recover after test to at least 12.4 volts, with 12.6 being the norm. With ignition off, a digital multi-meter connected at the pos. and neg. terminals, 12.6 is the fully charged voltae amount. Engine on, alternator will charge at about 13.8 to 14.5 volts when all is normal. If voltage of 12.4 can't be held by the battery with the engine off, or with the alternator charging, then the battery should be replaced. Cold weather will make these problems of dimming, ect. worse. The fix is to replaced the stock battery for the 1.8 Turbo or 2.0 with a battery used in the Diesel engine models. It is a tight fit, but with some wiggeling and moving the power steering fluid reservoir over to the left as far as you can ( do not disconnect the fluid hoses),just loosen the mounting bolts and remove from bracket, a larger battery will slide into the tray by placing battery with right end side down and over to the right. Now push the bottom end over to the right and push the left end down and over. Keep doing this and it will slide into place using factory battery tie down. The battery box top closes just as before. The insulation blanket can be cut in half and applied to the new unit by duct tape at the loose ends. This substantial increase in Cold cranking reserve and amp hours, ect. will make starting the engine in any temp. a non-event. Lights no longer dim, fan motor will not slow down, and the alternator doesn't have to charge as quickly or with the higher voltage. Our entire cars are electrical and this increase in battery output will stabilise the engine control systems, sensors, switches, motors and modules. In Montana in -30 degree F weather I had the chance to test out my new larger battery. I unlocked the door and turned key to on to allow the fuel pump to bring the fuel rail up to pressure. 5 seconds or less. I cranked the engine over and after only 3-4 turns of the starter, the engine started right up. I turned on the seat heat, the heated mirrors and the rear defrost. Headlights on and off I went, slowly until warm-up. VW likes the entire car to warm up as a unit. The heat was turned on with fan at 3. No dimming, hesitation, or fan slowing down or any off the previously reported problems.I have the cold weather package that uses a bunch of power and can place a load on a battery that will cause dimming, flickering, ect. Many owners up-grade the battery at the first replacement and report the same results. Sears now sells the Optima brand. A new Optima battery with a very low install charge is the ticket. They check out the entire electrical system to make sure it the battery thats failed and not the alternator. I assume you have the original battery??
One more thing I do for easy starts in extreme cold, is using Mobil 1, OW40 European formulation oil. It is thin when cold and stays thick when hot. It is one of the best synthetics, period esp. the OW40 formulation. I use it all year round here in Dallas.. Good Luck, JK