1.6 FSi temp Sensor

chrisnic

Member
Hi
I have a 1.6 FSi and the temp gauge barely moves from zero. If i leave the car ticking over on the drive for 10-15 mins then the guage goes up to normal temp, but if i get in and drive it straight away, it stays on zero, no matter how long i drive? I notice the temp sensor and thermostat look like they have been changed. Online the temp sensors seem to be green whereas the one on the car is black - is this the problem?

chris
 
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Hi
I have a 1.6 FSi and the temp gauge barely moves from zero. If i leave the car ticking over on the drive for 10-15 mins then the guage goes up to normal temp, but if i get in and drive it straight away, it stays on zero, no matter how long i drive? I notice the temp sensor and thermostat look like they have been changed. Online the temp sensors seem to be green whereas the one on the car is black - is this the problem?

chris

There are two separate senders, the black one normally controls the temperature for the radiator fan, the green one has 4 pins and feeds the Dash and the ECU.

So you may be looking in the wrong place.

The black one is normally in the area near the fan and the green one is (I believe) near the thermostat on the FSI.

I would bet that it is your thermostat that is giving the problem but you might as well change the sender too.

Steve B
 
I agree with Steve above.

Green one is on the opposite side of the coolant regulator assembly/thermostat housing youre looking at, very hard to see and access from above.

Here is a photo to prove how hard it is to see.

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Green star next to temp sender, blue star next to the connector that attached to it.
For reference the top of the photo is the edge of the engine block.

M679WuWXEiM.jpg

It does sound as if your thermostat has failed in the open position, so as soon as air is flowing through the rad the temperature drops back to 40-45degrees.
 
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Hi
The sender on the thermostat housing is black. Could it be the wrong sender? Why does the car heat up normally if left to idle for 10 minutes if the thermostat is stuck?
 
Hi
The sender on the thermostat housing is black. Could it be the wrong sender? Why does the car heat up normally if left to idle for 10 minutes if the thermostat is stuck?
The correct sensor has four pins it should be green but I suppose that there might be some aftermarket ones that are black perhaps? But it has to have four pins.

If you are idling a 1.6 it will heat up reasonably well and reasonably quickly with or without a thermostat, because you have no air flow and not much coolant movement at tickover.

When you are driving, the air flowing through the radiator cools the water down a lot, the thermostat closes to prevent that airflow from cooling the water too much..

If you do a test drive and switch off the heater, the temperature should start to rise a little more (the heater acts as a second radiator). If that does happen then it is pretty conclusive proof that it is the thermostat that is the problem. Because if the needle rises it proves that the sender is doing its job and it means you are running very cooll

Steve B
 
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I had almost the exact same exchange on the phone with an Audi specialist this week. He was adamant I had supplied the wrong sender.
I had sent the 4 pin green for 1.6fsi. He said it needed a 2 pin black.
As Birchall says count the pins.
I've never seen a modern VAG engine use anything other than a 4pin green connector temp sender.
Just to add, Audi specialist did eventually find the correct location and fitted the sensor I had supplied him.

If it is two pins and black you're looking at the wrong part. (that one has the connector end of unit facing towards the firewall/passenger compartment)

If it is four pins and (usually) green it is the correct unit.
The connector end on this unit faces toward the radiator

The car will heat up normally at idle because there is only static ambient air passing through the radiator compared to when the car is moving and air is moving through the radiator with velocity.
The car will naturally reach a temperature to open the termostat, the water pumped around the engine is then free to flow to the radiator if the temperature then gets too high the radiator fans will activate to pull cool air through the radiator.

Thermostats tend to fail in the open position by design, because an engine running too cool is nowhere near as catastrophic of an issue as a stat failing closed and causing engine to overheat.

If the thermostat is always open then the water used as a heat exchanger in the engine block is constantly moving through the radiator where a secondary heat exchange happens between the water pumped to the radiator and the air passing through the radiator when the car is moving.

The result tends to be a car that takes a long time to get to operating temperature on the move (if at all). Behaves like normal at idle.

Hopefully that's helpful, and you can get this sorted.
 
Will have a look at the weekend. You are right, the black one is facing toward the firewall, so must be correct. Thanks for the detailed explanation guys
;)
 
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