Thermostat control

[DG2004]

Is the ecm the only thing that controls the thermostat being told to open and close or is there also some direct affect from the water like a old school thermostat?

[Mike Tries]

My understanding is that our thermostats are actuated by hot water circulation, but that the thermostat housing has a little ECU-actuated heating element in it to... I don't know... facilitate the opening of the thermostat when commanded? Someone will correct me if I'm wrong. I saw your post in the other thread--you're experiencing a pegged temperature gauge, right?

[old guy]

The 1.8T has a mapped cooling system. This study guide is for a 1.6T engine, but the function is the same for the 1.8T Clicky click

[DG2004]

Yeah. I think I either have a short or ecm going not sure yet.( No vcds yet) I’m just doing the basic replacing stuff that needs it anyways first wiring, sensors, water pump thermostat ect. it keeps throwing the coolant sensor code and ecm code. Sometimes crank no start. The reason I asked about the thermostat ecm control thing is because everything was just replaced and I can see that it’s not opening (no circulation) just curious on if when I figure out the short or wiring problem if it would operate the thermostat.

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Thank you!

[old guy]

just curious on if when I figure out the short or wiring problem if it would operate the thermostat.

You can unplug the thermostat auxiliary heater (controlled by the ECM) and the mechanical portion of the thermostat will still operate regardless of the ECM input. It's really worth your time to read the Study Guide linked above to fully understand the mapped cooling system.

[DG2004]

Thank you Old Guy. I definitely will read it tonight. Thanks for the link.

[PSI NRG]

Hey old guy, I’m running ignitron standalone Ecu and with this Ecu you can lower coolant temps slightly. Over the summer I was seeing coolant temps of around 185F now lately I see around 206 which seems normal on the gauge cluster but according to the Ecu it’s warmer than normal. I’ve tried to bleed the system a decent amount but no change. Thermostat is new genuine, water pump is new genuine. When I rev the car to 3K temps go down a bit. Do I have a nasty air pocket? I know these cars can be a difficult to bleed. Any info would be helpful!


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[old guy]

Sorry for the delayed response. Stuff happens...

The OEM mapped thermostat operates at a fairly high temperature. With no input from the ECM it will run in the 208°→212°f range. This typically occurs during steady state driving under low load. As soon as you increase the load on the engine the ECM increases the duty cycle on the thermostat heater to lower the block temperature.

The coolant temperature gauge is not a linear instrument. It will indicate up to full temperature around 175°f and will not advance beyond that temperature until around 228°f.

[DG2004]

You can unplug the thermostat auxiliary heater (controlled by the ECM) and the mechanical portion of the thermostat will still operate regardless of the ECM input. It's really worth your time to read the Study Guide linked above to fully understand the mapped cooling system.

Thanks old guy. I read over the study guide.That is exactly the info. I was looking for. I’m going to to pull vacuum on it and fill one last time and see if that does the trick if not I looks like I’m
going to pull the water pump back out. I did isolate the top circuit just to take the rad out of the equation and it still wouldn’t pump. Is there a chance I made have received a reverse flow water pump? I’ve not heard of one for a 1.8 and I got a whole gates timing water kit made for the car so doubt it is.

[PSI NRG]

Thanks old guy. I read over the study guide.That is exactly the info. I was looking for. I’m going to to pull vacuum on it and fill one last time and see if that does the trick if not I looks like I’m
going to pull the water pump back out. I did isolate the top circuit just to take the rad out of the equation and it still wouldn’t pump. Is there a chance I made have received a reverse flow water pump? I’ve not heard of one for a 1.8 and I got a whole gates timing water kit made for the car so doubt it is.

What’s the actual issue you’re having? Overheating?


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[DG2004]

[QUOTE=PSI NRG;15141826]What’s the actual issue you’re having? Overheating?

The water isn’t flowing it’s like there is an air pocket still , the pump isn’t working, or it’s plugged up somewhere. I’ve already bled it manually with the screw and the heater core hose , then I actually stuck a garden hose on the heater core and back flushed the upper system. thinking I might clear a blockage. I’m going to a vacuum bleed on it tomorrow and see if that does it.

[PSI NRG]

So it’s like there’s an air lock? That can happen too. Could be in the radiator as well. If it’s original to the car might be a good idea to try and flush it or even toss in a new one.


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[egovreau]

[QUOTE=DG2004;15142126]

What’s the actual issue you’re having? Overheating?

The water isn’t flowing it’s like there is an air pocket still , the pump isn’t working, or it’s plugged up somewhere. I’ve already bled it manually with the screw and the heater core hose , then I actually stuck a garden hose on the heater core and back flushed the upper system. thinking I might clear a blockage. I’m going to a vacuum bleed on it tomorrow and see if that does it.

The heater core is an open loop so if your heater core is clogged, the worst that will happen is no heat in the wintertime.

[Mike Tries]

I'm curious if this was resolved. It ended up being one of the more interesting failure modes we've had in a while.

[DG2004]

Well… I thought I let everyone know what the problem ended up being. I replaced the entire cooling system and it didn’t fix the problem. So I took it all apart again pulled the new thermostat apart and put in a pot of boiling water and wouldn’t you know it in the end the new crappy aftermarket thermostat was stuck closed. All is fixed now on cooling.

Just put a new 219 relay in and it was crap off the shelf too. I’m not sure what going on with quality control in China but it sucks.

[PSI NRG]

I had a junk genuine audi thermostat too out of the box


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