[1.6 FSI] - Exhaust Gas Temperature Vs. Coolant Temperature

Evripidis

Member
Hi all,

I would like your opinions on the following:

1. I have gone through another minor round of repairs, i.e., skimming the plastic thermostat housing after it leaking due to a deformation. It is less than 5 years old but the symptom has lead me to believe that it must have gone through its cycles and/or overheated.

2. Other symptoms included; coolant overflowing and several leaks here and there. These facts had led me to believe that there must be a crack in the block somewhere and/or head gasket failure.

3. During the same period I have also replaced the exhaust gas temperature sensor that has been playing up with erroneous readings. I order as many parts as I can for all the cars that I service in one go to make save on shipping so I had it lying around.

4. It has been 2 days and 5-6 short runs including, two full cycles of reaching the operating temperature while being static with an industrial (huge) fan blowing at the front. The fans cycled fine.

5. I have yet to spot a leak, touch wood, but could the new temperature sensor cured the high temperatures? Surely the ECU must adjust the fuel mixture to close the control loop. So, erroneous exhaust temperature readings could lead to lean mixtures thus higher temperatures.

What do you all think?

Evros
 
I believe the FSI engine, well, coolant, runs at two different temperatures depending on load and road speed (and other parameters I'm sure).
Generally, in town driving the thermostat opens at around 110 C, this is controlled by a simple wax capsule. At motorway speeds, the thermostat opens earlier, at around 90 C, triggered by the ECU heating a resistor in the wax capsule, to melt the wax, and open right thermostat.
So coolant temperature should not be influenced by the EGT sensor, but you're right, if the EGT sensor tell the ECU that the EGT is too high, the ECU will increase fuelling to bring it down. Equally, if the ECU thinks the engine temperature is too low, it'll weaken the mixture, and that would increase the real engi, ne temperature, maybe above the ability of the cooling system to bring it down. Your theory could be right!
Only my theory though ...
Mac.
 
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