csouther

I noticed the other day on the freeway the temperature gauge war reading 3/4 instead of its normal 1/2. I drove this car last year through the mohave desert and it held 1/2 the entire way. Its 32F outside and now it goes up to 3/4. If I stop and idle for a while it will come back down. I logged the various temperatures and found the coolant never got hotter than 112 and the oil 110. How hot do these normally run and are there more than one temperature sensors? I am leaning towards bad sensor or thermostat, though the engine doesn't take very long to warm up.

attached is the datalog showing it start at 1/2 gauge going up to 3/4 and then back down. After looking at it it looks like it tries to open the thermostat but the temperature still keeps rising and the differential between the engine out and radiator out is large. I'm leaning towards sticky thermostat but I'd like someone that has more experience or smarter than me to confirm my thoughts.

Thanks in advance!

raj99

when was the last time you changed the coolant in the Q7? Also, I assume the reservoir looks good and it's at the right level? In most cases, when the thermostat goes bad, it'll be stuck open, which won't cause the condition you described. However, if the waterpump is gone...well that can certainly cause and overheat condition.

csouther

I have only owned the car for 8 months and never changed the fluid. The level looked fine when I checked yesterday. The weird thing is when it gets hot I can open the hood and touch the return side of the radiator and it's not very hot. The inlet side it hot but you would think both should be somewhat hot if the engine is supposedly running at 114C. I can feel the difference between 60C and 114C no problem. What if it's stuck partially open? Or I guess a bad waterpump could have the same symptoms. Low flow qould allow the radiator to remove a lot of heat from the coolant before making it to the outlet side of the radiator.

How many temperature sensors are on this and where are all of them. I only see the one on the drivers side radiator hose up top but VCDS reports engine side temp and extit radiator side temps along with the differential between the two. Is there another one tucked up on the passenger side down below? The car has 140K on it so maybe I'll just put a new pump and t-stat in it and see what happens.

smith2010Q7

Coolant Pump and Thermostat
(The 4.2L V8 FSI engine in the RS4 does not use the mapcontrolled
thermostat as found in the Audi Q7 engine.
To achieve more effective cooling, two additional coolers
are used. Coolant flows continuously through one of
the additional coolers. The second additional cooler is
opened via a coolant thermostat.
To avoid excessive heating-up after shutting off the hot
engine, the coolant run-on pump is activated a preset
period of time after the engine is shut off. The pump
run-on time and the need for additional activation
of both radiator fans are determined on the basis of
characteristic maps. Various measured quantities
are included in the calculation (engine temperature,
ambient temperature, engine oil temperature and fuel
consumption).

The cooling system in the new V8 engines was configured
as a longitudinal-flow cooling system. The cooling water
flows in on the outlet side and through the cylinder
head gasket into the cylinder head, where it flows out
longitudinally through the chain housing cover.
Cooling of the cylinder webs was improved by drilling
coolant ducts with an optimized cross-sectional area into
the webs. Forced flow through these bores is ensured by
means of specially sealed water ducts.
The high-revving engine also has two V-shaped forcedflow
bores between the inlet valves, because they are
subjected to higher stresses due to the high power
density.
A map-controlled coolant thermostat is used in the basic
engine.

When operating at full throttle, the coolant temperature
is reduced to 90°C via an electrically heated thermostat
to avoid increasing the tendency of the engine to knock.
When operating at part throttle, which is not critical with
regard to knock, the coolant temperature is increased to
105°C. The thermodynamic advantages and the reduced
friction result in a fuel saving of approximately 1.5 %
when operating at low part-throttle.

The Engine Control Module (ECM) J623 activates Coolant
Fan Control (FC) Control Module J293 and Coolant Fan
Control (FC) Control Module 2 J671 by generating a
separate PWM signal. The coolant fan control modules
then energize the coolant fans based on the ECM signal
by means of a PWM signal. The radiator fan is activated
by the ECM based on a characteristic map.

upgraded 4.2.
You have one sensor.
Inlet to the thermostat and pump to the engine block should be cool, then outlet from the back of the engine to the sensor plus outlet from the oil cooler to inlet to the RAD on the passenger side should be hot.

I am looking more toward your fans, did you have any codes for them like open circuit?

csouther

The fans re operating normal as described in your last post. There are no codes for anything surprisingly. I bought a new t-stat and water pump and will swap those out first since its due anyway and is likely the issue. I'll let you know what happens.

Krazyexp