Low Coolant Level? Diagnose & Troubleshooting.

Hello,
I have now received my diagnostic hardware and I spent some time today measuring various parameters of my 1.9 engine. I have already posted several threads here regarding my problem.

"The error code was empty... I went through Ulf's troubleshooting guide for VAG Com completely, but everything seemed fine except that the boost pressure builds up a bit too slowly. The only thing I noticed while examining my measured values was that the coolant temperature, according to VAG Com, was between 72-76°C during driving (76°C only during longer drives at 3500 rpm). It's very strange that my dashboard display shows an optimal operating temperature of 90°C. Could this observation explain my loss of power? Are there two coolant temperature sensors in the car? What is defective in my case? Does my car (G3, manufactured in December 1994, 1Z) have a kind of coolant heater? I found three glow plugs on the right side of the engine block in the hose for the interior heating."

Greetings.
Reuselkopp.

Hello Reuselkopp!

Feed the search function with the following term: Plateau function .
You will quickly realize that the digitally smoothed coolant temperature display is not much help for a system check.

Your coolant temperature is clearly too low. It's very likely that your thermostat valve is defective and either opens too early or doesn't close properly anymore.
It could also be that the temperature sensor is defective. Please check the VAG-COM reading at a completely cooled-down engine (ideally overnight) to see if it's plausible.

You also have a glow plug heating system on your 1Z that electrically heats the coolant as it flows to the heater core.

Regards,
Alex.

Hello,

Okay, I understand the part about the plateau function. Since my sensor read approximately 8°C this morning when it was already cooled down, I would also rule out the sensor itself. Then it's more likely to be the thermostat.
But what is much more important to me is whether this would also explain the loss of power. Is there a "limp home" mode controlled by the engine control unit (ECU) until the engine reaches its operating temperature?

Greetings.
Reuselkopp.

Hello Reuselkopp!

Feed the search function with the following term: Plateau function .
You will quickly realize that the digitally smoothed coolant temperature display is not much help for a system check.


It doesn't have to be that way. My '94 Passat didn't have that feature...