Changing coolant temperature sensor on 2.5 TDI
The fault symptom I had is the temp. gauge that had always remained pegged at 90 C started moving around.
I knew it could be a no of things including a bad earth,thermostat, gauge or sender. I connected up VAG COM & noted that while that showed 90 C coolant temp. the gauge on the dash was going down. A bit of research revealed that the senser is 2 parts [4 wires]. One half drives the temp gauge, the other the ECU.
I now had to find where the sensor was as these are a known common problem. I knew roughly were it should be but a quick look with a torch revealed a dirty mess of oil, obviously spilt by a careless mechanic. [Another reason to service your own vehicle]
After jacking & removing the belly pan/sound absorbing panel, moving the radiator forward & covering the alternator, the area was thoroughly cleaned using brake clean & a brush.
Just to the right of the alt. & between no1 & 2 injectors is a plastic housing bolted to the engine. There are a couple of sensors there, the one we need is in the front & is normally green. Mine still had the original black one.
Next step is to drain the coolant using the drain plug.
It's easiest to remove the sensor with the wiring plug still connected.
Just removing the connector proved a challenge. The one on the Polo, that I had just done, came away easily. I probably fiddled for around 10 mins. before it came off. By inserting a small screwdriver into the slot & turning it releases a plate inside. If you turn it too much it reingages the hook on the sensor again.
Others have said it is an easy job to change the sensor but I found it quite fiddly.
I finished up using a broad long nose pliers gripping the edges of the plastic clip at the bottom of the U shape. By pushing the sensor in enough to compress the soft O ring, the clip is slid upwards into the slots in the housing. If you are blessed with 3 hands that could be an advantage.
Replace or renew the coolant, run engine with heater in hottest position & open bleed screw on hose at the top to remove any air.
Notes.As already said these sensors have a limited life, in my case around 9 years , in the Polo as well.
If the other part fails it will give erratic idling as I experienced in the Polo while the temp. gauge worked normally.
According to Haynes publishing " The sensor contains a thermistor, which consists of an electronic component whose electrical resistance decreases at a predetermined rate as its temperature rises. When coolant is cold, the sensor resistance is high, current flow through the gauge is reduced, and the gauge needle points towards the COLD end of the scale"
The part no of the green sender is 059 919 501A [suits most VWs] My van has the ACV 2.5 TDI engine. I have purchased two of these senders, the first [genuine] cost $ 58.35 trade without a new clip.
The second one that I purchased on Ebay UK was aftermarket [kit included O ring & clip] & cost just under $18 with registered post to the local post office. The brand is febi & looks like a Bilstein company.
I have just bought another from Amazon for $12.39 + $2.71 postage. This is a genuine part with the VW & Audi logos but made in China.
Although ordered from Amazon, it was posted from Hong Kong, hence the cheaper postage.
Last edited by jets; 29-03-2013 at 09:35 PM.
Understand how it works, troubleshoot logically BEFORE replacing parts.
2001 T4 TRAKKA Syncro 2.5TDI,2006 Mk5 2.0TDI Golf manual,2001 Polo 1.4 16V manual [now sold], '09 2.0CR TDI Tiguan manual,
Numerous Mk1 Golf diesels
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