Bleeding the coolant system?

[Eddie]

Alright!
Just read Scott16v Coolant post. Got similar problems.
I've just changed the water temp sensor on my 16 valver, which was slightly different from the original one ( Nipple connection rather than a male spade connection). I also changed the top and bottom rad hoses which had perished.

Refilled the system, Thermostat opens and fan kicks in and water pump...pumps.
The gauge now works and the system now longer leaks, HAPPY DAYS!

However i have since noticed the gauge rises fairly rapidly up the 3/4 increment and moves slightly about this point when moving and stuck in traffic. This is a lot higher then the needle would normally travel with the old sensor. Also the water warning light flashes sometimes.

Is this due to the new sensor? Or have i maybe trapped air in the system?

car has recent new head gasket, water pump, expansion tank and rad.

Any advice welcome. Cheers.


 

[Leon R]

Sounds like its overheating? What does the oil temp read when the light flashes?

Take the rad cap off, run the car and have a bottle of coolant top up ready. I normally keep squeezing the top and bottom rad hoses, if you feel bubbles rushing around inside then you have air in the system.

Did you compare that the sensors are the same? EuroCarParts kept on giving me the wrong oil pressure switch ones!

[rubjonny]

what does the oil temp say, normal operating temp is 1/2 on the gauge, up to 3/4 in traffic is ok as long as the fan cuts in and keeps it there.  was the sender a gen vw one?

[Eddie]

Hi,
Sorry for the late reply, car seems fine now. gauge operates fine, still get the flashing level light some times.
The oil temp is about the same as before, hovers between 96 - 102 degC when warmed up.
I've squeezed the hell out of the top and bottom rad hoses. I've got forearms like popeye squeezing them.

I'll have to tinker with the light sensor.

Am i right in thinking it senses high water temp as well?
 

[DarnPB]

The oil temp is on the high side but perfectly acceptable. Don't forget that the oil is cooled by the engine cooling system.
The water temp should be around 90, but it can go up past 105 due to the cooling system being a closed pressurised system.
When you try to bleed the cooling system again, remove the blue or black sensor before filling, then fill the system slowly until water comes out from where the sensors should be. This position is fairly near the top most part of the system and trapped air can escape from this position. Then refit the sensor.
As said before, remove the water filler cap and start the engine with a full bottle handy, but be aware that when the water temp gets up to normal operating temperature, the level of the water will rise and can overflow.
DO NOT ADD COLD WATER TO A HOT ENGINE. YOU CAN BREAK IT.

[rubjonny]

oil temp is perfectly acceptible, if a little lower than most valvers run!  the light also warns of an overheat condition, try swapping the red/yel wire to a different sensor and see if it reads as high.  if the sensor was a gsf one that might be why, they dont tend to read correctly.

[Eddie]

 :smiley:Cheers lads, the header tank is a GSF one. The second one I've had to change.
Probably get a VAG one if the problem persists.

The last two times I've taken it out the light remained off, cross fingers it stays that way.

For the first time since buying the car in 2004, the cooling systen hasn't leaked from some area or another.
It's great to open the bonnet for the weeekly engine check and not have to add anti-freeze.

[Conker]

I've bought a non-VAG expansion tank and its causing me a flashing temp warning light too. To check if its that, bridge the pins on the head tank connection socket (I used a paper clip !!). If the light doesn't come on anymore, you've found the problem.