Starting problem ALH

Hello,
I'm having a problem with my ALH-TDI, and it's like this:
Morning cold start, no problem.
Warm start, no problem.
Cold start, driving for 2-3km, so the engine doesn't really warm up. Turn off the engine, go shopping (or something for 1-2 hours), try to start it, and it doesn't start, or it only starts after a long cranking.
I noticed that when attempting to start, it doesn't glow, even though it probably should, given the outside temperature of 0-2°C.
I then unplugged the coolant temperature sensor, and sure enough, it started glowing and the car started. Is the problem now only related to the temperature sensor, or are there other possible causes for this issue? The engine is otherwise in perfect working order, it's an ALH model manufactured in June 2002 with 50,000 km on the odometer.

Regards,
Hanni.

Hello,
I'm having a problem with my ALH-TDI, and it's like this:
Morning cold start, no problem.
Warm start, no problem.
Cold start, driving for 2-3km, so the engine doesn't really warm up. Turn off the engine, go shopping (or something for 1-2 hours), try to start it, and it doesn't start, or it only starts after a long cranking.
I noticed that when attempting to start, it doesn't glow, even though it probably should, given the outside temperature of 0-2°C.
I then unplugged the coolant temperature sensor, and sure enough, it started glowing and the car started. Is the problem now only related to the temperature sensor, or are there other possible causes for this issue? The engine is otherwise in perfect working order, it's an ALH model manufactured in June 2002 with 50,000 km on the odometer.

Regards,
Hanni
Hello,
Just replace the temperature sensor!
It's not that expensive, really.
Best regards,
Günther.

Hanni wrote:

I then unplugged the coolant temperature sensor connector, and lo and behold, it started glowing and then it started up. Is it only due to the temperature sensor now, or are there other possible causes for this problem?

Yes, a lot:
Okay, I'm ready. Please provide the German text you want me to translate.
The only thing that can probably be ruled out in advance is the preheating system.

It's normal for it not to need to be preheated again after a short trip and a 1-2 hour standstill (due to residual heat in the engine block).
-> Before replacing the sensor, I would first check its plausibility using VAGCOM to see if it's reading reasonable temperature values. Because, let's be honest, this thing isn't exactly cheap.

Okay, here's the solution to the puzzle:
'There always seems to be air getting into the diesel line. The mechanic replaced the diesel filter, but that doesn't seem to be the problem. There are still air bubbles in the fuel line.' Then a valve was replaced, and the problem has not occurred since.
Hanni.

Hanni wrote:

Okay, here's the solution to the riddle: "There always seems to be air getting into the diesel line. The mechanic replaced the diesel filter, but that doesn't seem to be the problem. There are still air bubbles in the fuel line." Then a valve was replaced, and the problem has not occurred since. Hanni

The temperature-controlled valve for the return line in the diesel filter?

"A few more concrete descriptions of the solutions would be helpful, because what else are people supposed to do with this topic if they're experiencing the same problem?"

Best regards, Rainer.

@Hanni

What exactly was the problem? I also know someone who is experiencing the same issue. I haven't taken a closer look at the car yet, but I'd like to know what the problem was for you.

Thanks,
Best regards,
arne

The temperature-controlled valve for the return line in the diesel filter?

'A few more concrete descriptions of the solutions would be helpful, because what else are people supposed to do with this topic if they're experiencing the same problem?'

Greetings, Rainer

Hello Rainer,

I believe it was the return valve in the diesel filter, but I haven't received the invoice yet. I hope it's clearly stated again there.

Regards,
Hanni

Could you perhaps explain the term "air bubbles in the fuel line" in more detail, referring to your car? I'm also experiencing significant starting problems when the engine is warm. However, I could only detect one air bubble in the fuel line. It has a length of approximately 5-6mm along the line.
Thank you.

5-6 cm is already way too much!

The sensor in the ESP system can no longer function reliably. And if your injection timing is no longer correct, you will also experience difficulties starting the engine.

This topic has been discussed extensively and frequently, including by me. By now, troubleshooting procedures should be known for every engine and vehicle. The solution is usually very simple; it's often a clogged diesel filter or a leak in the valve/pipe.

Best regards, Georg.

@Georg-TDI
It's only 5-6mm. Of course, I had done some research beforehand, and in particular...
Okay, I understand. Please provide the German text you want me to translate into English. I will only provide the translation.

Here are some of the things I took care of in advance:
I took my car to the service center for its inspection today (it was necessary due to the warranty). Of course, they noticed this extreme (4-5 second) cold start problem. I've tried several ways to fix this, but none of them have worked.
Cold start is perfect, mileage is 85,000 km.
Done: Had the battery checked.
Starter cleaned, brushes checked and lubricated.
Cable junctions cleaned.
Diesel filter replaced.
Just a small air bubble in the diesel line - I think it's okay.
Removing the temperature sensor results in the engine starting warm immediately.
Error memory - empty.
verschandeln the air filter and the filter screen (inlet to the air filter).
Fuel injection start verified and OK.

That's why the question is whether a single air bubble is okay or not. In the discussions, it's always about air bubbles – specifically, larger or numerous ones. Since none of my acquaintances drive a TDI, I unfortunately don't have anything to compare it to.

The friendly mechanic wanted to replace the starter motor right away and claims that the new starters have higher performance and a higher RPM. Has anyone ever heard of this before?

Hi.

Quote:

That's why the question is whether -a- air bubble is okay or not.

When the engine is off, a small air bubble isn't very significant, unless it indicates that half of the line has been emptied.
It is important that while the engine is running, there should not be a constant stream of air bubbles or foam.
Okay, have someone start the engine and see what happens.

Best regards, Rainer.

@Georg-TDI
It's only 5-6mm.

Oops...

Sorry, my mistake! I hadn't had any coffee yet.

A 5-6 mm air bubble is, of course, not a serious problem.

Since you mentioned that the car is still under warranty, I would recommend taking the starting problems you're experiencing to the dealership and having them fixed under warranty.

Based on what you're describing, the problem seems to be with the starter. I think you probably have a '99 model or older. There were known issues with the starter on those models. If you disconnect the temperature sensor, it should start up normally. That's actually well-known among the friendly people.

Best regards,
Mattes

Okay, I've checked the fuel line. There are no more air bubbles or foam coming out with the engine running. I think I'm going to have to bite the bullet and buy a new starter. I'll post again later to see if it's better.