suspicious coolant temperature data

[Paul_B]

I just bought a 2001 Beetle with 2.0L gas engine, automatic transmission, 99000 miles.

This car doesn't have a temperature gauge and I was suspicious of the blue coolant light so I had my wife take it for a 40 or so minute drive while I read the coolant temperature off my code scanner and recorded the results on paper.

The drive was a mixture of highway and in town roads (no traffic). Outside air temp was about 80f.

My scanner (Actron) showed 2 different coolant temperatures one called $10 and another called $1A.

The data from the 2 channels was different, the $10 channel was usually about 15 or 20 degrees cooler than the $1A channel.

$10 ranged from about 181f to 205f.
$1A ranged from about 198f to 221f.

I think these are both too hot, do you agree?

Also the blue coolant light is suspicious, if often takes a long time to go out, sometimes never goes out, and once it started flashing blue. It has never been red. The fans also never come on, but I know they are working because I turned the AC on and they came on.

Should I just replace the coolant temperature sensor with the new green one and repeat the test?

Thanks

[MyOtherRidesAVette]

It would not be unusual for the blue light to stay on after an overnight cool down and a morning temperature at maybe 80°, for 10 minutes or so. A flashing blue light indicates a blue flashing light indicates a problem in the electrical section of the cooling system, and a flashing red, low coolant level. The fans typically don't run if the car is in motion, the natural air flow is sufficient to keep the system at temperature. They will sometimes come on, even after engine shutdown and could run for 10 minutes or so as the system tends to continue to heat when it is no longer flowing through the radiator and dissipating the heat.

The extended solid blue light, coupled with the flashing blue light could indicate a coolant temperature sensor failure. I'm sorry, but of the top of my head I don't know the specs thermostat opening or system temperature running range. I'd have to look then up. I'm also not familiar with the history of the cooling system that brought you to this point.

I can offer for your review, the complete Bently system diagnostics -

Bentley Cooling System Diagnostics
Overheating problem

Bentley drain and fill procedure
Beetle overheating

MORAV

[simonsi]

Originally Posted by Paul_B

I just bought a 2001 Beetle with 2.0L gas engine, automatic transmission, 99000 miles.

This car doesn't have a temperature gauge and I was suspicious of the blue coolant light so I had my wife take it for a 40 or so minute drive while I read the coolant temperature off my code scanner and recorded the results on paper.

The drive was a mixture of highway and in town roads (no traffic). Outside air temp was about 80f.

My scanner (Actron) showed 2 different coolant temperatures one called $10 and another called $1A.

The data from the 2 channels was different, the $10 channel was usually about 15 or 20 degrees cooler than the $1A channel.

$10 ranged from about 181f to 205f.
$1A ranged from about 198f to 221f.

I think these are both too hot, do you agree?

Also the blue coolant light is suspicious, if often takes a long time to go out, sometimes never goes out, and once it started flashing blue. It has never been red. The fans also never come on, but I know they are working because I turned the AC on and they came on.

Should I just replace the coolant temperature sensor with the new green one and repeat the test?

Thanks

Only temps I see on vagcom are intake air and coolant. Coolant temp can go high, that is why the system pressurizes to 15psi.

Your CTS is almost certainly bad giving the flashing blue so replace it first. Then see what temp it gives you.

The CTS has two measuring coils in it, one for the ECU and one drives the indicator blue/red light. The switch from blue to off takes place at around 67deg C. It is possible for the ECU side to be good but the light side be bad (and vice versa), so the engine can run perfectly but the light give wrong indications...

[Paul_B]

Thanks for the help, I'll replace the sensor. I was wondering why it had 4 contacts in the electrical connector. The good thing is that it's a cheap part and looks like an easy job.

Another question. I've read online that it's very bad to mix the VW coolant with other brands, that it turns into a gel. Is this true? If I ever need to refill (or change) the radiator fluid do I have to drain it completely and flush with water before using another brand, or can I just mix another brand with the VW fluid?

[simonsi]

$20 part typically. Make sure you get a new clip when you get the new sensor. Push down on the sensor when you slide the clip in else the clip will break/bend/snap.

Yes it is bad, and you don't need much of the wrong kind. When we got ours I did a water pump and TB change, coolant looked dirty brown so I just topped up with G12, after a day it overheated and I found the coolant flange and heater hoses literally blocked with pink gel....

Drain old coolant, refill with plain water, run engine for 5mins after warm. Repeat twice.

Drain water. Refill with 60-70% G12, it will be diluted with the plain water still in the block down to the normal ratio.

If you don't refill and run, old coolant mix can be left in the engine block, ready to react with the G12 if the wrong kind....

[Smileybug]

If you need to top up, top up with some water. Buy some G12 and keep it in the car too. Its not really that expensive and then you're safe. DO NOT MIX COOLANTS.

[Paul_B]

Originally Posted by simonsi

.... When we got ours I did a water pump and TB change, coolant looked dirty brown so I just topped up with G12, after a day it overheated and I found the coolant flange and heater hoses literally blocked with pink gel

It's funny you mention that situation. I just bought this car from a used car dealer and he put in a new WP and TB and don't know if he is aware of this issue. I checked the fluid in the reservoir and it's not gelled, so I'm hoping the mixing has not occured.

If he did mix fluids I wonder if that could be contributing to my high temperature problem. Of course I don't really know if I have a high temp problem until I change my sensor. Maybe I should do the water flush, new coolant treatment described above when I do the sensor.

Thanks for the help and advice.

[geniushanbiao]

I think your temp is probably fine. However you should use a VAG-COM to read it. You can buy a cable from Ebay for like 15 bucks and then run it with VCDS-Lite or something else. With my VAG-COM, mine reads 99C when running but the CTS and fan switch, fans are already new...The fan turns on normally and both low and high speed runs. I don't know whether this temp is normal either...