Cooling Help

[Zackattack]

Hello,

I'm trying to troubleshoot if my cooling system is working properly on my 2.7T 2004 A6. When the car is running I can't see any coolant flowing into the reservoir. I was going to pull hoses off when cool with the car started and see if there is any flow. Does anyone have a diagram of the flow path?

I ask because I have a cheap OBD adapter just to see engine coolant temp. I was using Torque app on my phone and the temp would get to 224 degrees F so I thought the app might be screwed up. Then I got OBD car doctor app and the temp was fluctuating between 140 and 220 degrees F. The needle in the car stays at 12 o'clock and I used a fluke laser thermometer to measure the temps when the car was up to temperature. I got 180 degrees F at the highest spot and that was at the engine output hose to radiator. It's driving me nuts, I wish I never got the app and was just bliss in ignorance referencing the gauge in the car.

Is it possible that the sensor can be bad and no matter how high the temp gets the gauge will always stay at 12 o clock? I am thinking of machining an adapter that fits into the ECT port and accepts the ECT but has another port to screw in a temp gauge so I can see the "real" temp.

This is the reservoir. The two hoses I'm wondering about attach to the circled areas. Is coolant always flowing thru the hoses connected here? So if I remove them, coolant will come out while the car is running?



Please help me if you can.

[AudiNike12]

The left connection isn't visible here. Don't know why

[chris86vw]

This is the reservoir. The two hoses I'm wondering about attach to the circled areas. Is coolant always flowing thru the hoses connected here? So if I remove them, coolant will come out while the car is running?



Please help me if you can.

Coolant is not necessarily always flowing through the reservoir, it is really just an overflow/expansion tank supplying more coolant or taking excess depending on the temp and pressure in the rest of the system. The in out diagram that someone just posted up is only showing one of the fittings you have circled, the other is a vent.,

the connection to the left of 10 in his pic is the outlet (like that diagram shows) on the bottom and not in your ecs pic, The connection next to circle for the cap is the inlet and the item in the lower left of your picture.


What you circled on the right hand side of the res is the line for the over flow tube. if you dig around you will see it is only about 8-12" long and just dumps by the frame rail. If the reservoir was overfilled and the system exceeds the pressure the cap is set for it will blow off excess pressure/coolant via that hose and a little channel in the reservoir you can't really see.

[chris86vw]

Oh also the range you are describing that you see with the scanner while the guage shows straight up.. is how it is supposed to work sort of. It seems a little wider of a range than it should be but it does have a huge range for "normal"

Maybe someone has the actual range somewhere I'm blanking.

[Zackattack]

So 190 - 224 degrees F is an acceptable temp range for this engine? Again, that's just what those apps say, I won't be able to measure until summer comes and I have my other vehicle out. This car is just my winter mobile because of the quattro and all. I replaced the thermostat, water pump and hoses when I rebuilt the engine 800 miles ago. The only thing I didn't replace was the radiator because I stuck a hose in the inlet and water flowed to the outlet with no issues. The PO had mixed coolant which caused a "gel" type substance to occur in the engine. This was most apparent in the rear main cover, which is exactly where that port at about 7 o'clock in the picture hooks to. Before I go ripping the front of the car off to get to the thermostat (PITA) I need a sure fire method of determining if it's bad, or exactly what is bad that is causing these temps.

[Zackattack]

Also when I say the temp is fluctuating on the app I mean just that, on graph mode it's just peaks and valleys. I wondering if it could be the bi-metal in the sensor has stopped working as it should?

[chris86vw]

So 190 - 224 degrees F is an acceptable temp range for this engine?

190 is technically about normalish but it will go higher.

224 is likely too high.

What I'm saying is that straight up on the gauge is a range of about 30-40 degrees depending on the vehicle. So that people don't freak out when they see it moving around too much. So yes it potentially could move quite a bit like you see in the app, I just can't remember through what range.

[Zackattack]

Well the sensor is 10$ so I think I'll pop one of those in and see what's up. However, if I have a stuck thermostat is there a way to put 12v to the after run pump and see if the coolant is flowing on a cold engine? I mean I can put 12v to the pump but is there a hose I could pull and see if it continuously pumps fluid?

[rollerton]

I can tell you that the temp gauge is designed to make the needle sit in generally wide areas, it doesn't move based on the actual coolant temp (unless you're very sneaky and good with Hex code). The way the eeprom is written the gauge shows "cold" and gets the needle moving as the coolant warms up. But it is not a linear representation of the temp. The cluster is programmed in such a way that the needle sits at 'normal' while the engine is warmed up even though the coolant can fluctuate something like 30-60* without moving the needle.
So, between around 170-230'ish (rough estimate) the needle just sits straight up. It will move if the temp goes outside of this range obviously.
We know this is true because smart hackers like Daz (RIP) reverse engineered the programming on the clusters years ago. They found the part where the code controls the needle action and found that when graphed the slope of the temp vs. needle position goes steadily up, then flat *(where the needle represents 'warm') , then starts increasing again. It's basically programmed to sit at the middle and not move unless the temp changes quite a bit.
Changing the values at the temp scale addresses in the eeprom to represent a steady upward slope will make the needle represent actual coolant temp, and it'll move around in real time (I did this on my old Mk4 GTI and it was a mixed blessing..). The reason for this (supposedly) is that the average person becomes distracted by changing gauge readings and they don't think our brains can handle that kind of stimulation. So they only show us gauge info to the extent that it informs us of the IMPORTANT things happening.

Also, from experience I can tell you if you have a stuck thermostat, you WILL know. It'll overheat, very obviously. Or if it's stuck open it'll over-cool when coasting..

[Zackattack]

Ok, so it sounds like it's not a stuck thermostat because it hasn't overheated. Obviously not the water pump because it hasn't overheated. That leaves the radiator and sensor as possible reasons right? Is there a spot on the heads that I can access while the engine is still in the car to tap for a mechanical water temp gauge?

[Calif_Kid]

Well the sensor is 10$ so I think I'll pop one of those in and see what's up. However, if I have a stuck thermostat is there a way to put 12v to the after run pump and see if the coolant is flowing on a cold engine? I mean I can put 12v to the pump but is there a hose I could pull and see if it continuously pumps fluid?

For checking the sensor, maybe just look at the temp reading (Vag-Com etc...) with the car off, and then at idle, and eventually at normal operating temp, and see if there are short term fluctuations in the reading. Like with the engine cold, the temp should display a steady reading of say 70F, and if you see some fluctuations, then replace the sensor.
- Jim

[Zackattack]

Has anyone installed a mechanical or electrical aftermarket water temp gauge? I would like to install at the head because I like seeing the actual temp all the time but I can't find any write ups on this.