Clear Lead: How to Gain and Maintain It

Hi.

A 2000 Leon ASV has a hard time starting when the temperature is around 5 degrees Celsius. It starts well when it's warmer, and it also starts well when it's cold enough to glow.
After being placed, there is always an air bubble, similar in size to the one in a spirit level, at the front.

So, this weekend I replaced the four aging hose clamps on the drip irrigation system (Gardena screw clamps).
There was a significant amount of noise when disconnecting the pre-stage from the ESP.

Did we have a vacuum there (which shouldn't be there), or is it normal because the diesel column needs to flow back into the tank, and therefore "pulls"?

I never paid attention to that when I switched my other devices.

"Thank you."
m;

Hi

A 2000s Leon ASV has trouble starting when the temperature is around 5 degrees Celsius. It starts well when it's warmer, and it also starts well when it's cold enough to glow.
After being placed, there is always an air bubble, similar in size to the one in a spirit level, at the front.
(..)
Did we have a vacuum there (which shouldn't be there), or is it normal because the diesel column needs to flow back into the tank, and therefore 'pulls'?
m;

Hello Martin,

The Leon ASV model exhibits exactly the same behavior.

Starting issues: I think there's a messed up calibration in the engine control unit that doesn't control the preheating duration proportionally to the outside temperature. Below 5°C, it seems to be inversely proportional to the outside temperature; above 5°C, it seems to switch to a 'summer mode' and sets a fixed preheating time. Apparently, in Spain, it's either significantly above 5°C or significantly below 5°C .
I'm not familiar with this behavior from Audi vehicles.

To the airbase:
The air bubble that forms in the return line after the engine is turned off has occurred in my Seat, my Audi, and, if I remember correctly, also in our Golf2 TD.
The diesel pump outlet leads downwards, behind the filter. This means that gravity will cause the diesel to flow back into the tank if the return line can draw in air. Therefore, this behavior is normal for IMA.

Best regards, Jochen.

Okay, let's speculate, because I simply don't know. Please correct me if I'm wrong. This is about the operating principle of this temperature valve on the diesel filter.

Quote:

Did we have a vacuum inside (which shouldn't be there), or is that normal because the diesel column needs to flow back into the tank, and therefore "pulls"?

Shouldn't the fuel line leading from the fuel filter be the one that returns to the tank? You have a pre-pump there, but still. The reason for my statement is that there's a temperature valve on the filter. If it detects cold diesel, it should shut off the fuel return to the tank. Therefore, it shouldn't start drawing fuel until you bypass the fuel return from the valve, or until the diesel temperature is still high enough after driving.

Then there's the possibility that the pre-pump is sealing correctly (like a pressure hold in a gasoline engine, which you apparently don't have), but the volume of diesel decreases as it cools down. In a sealed system, you would also get a vacuum as soon as the diesel temperature drops below the switching threshold of the valve.

If the valve is simply a flap that only redirects a large portion of the cold diesel back to the filter, you should probably just forget everything I've said.

Tom.

It's about ASVs - those good old VP37 tanks.

_I_ have a driver's license, but the lady who drives the Leon does not .

m;

Martin, so it doesn't necessarily have to be the flow *from* the distributor to the tank, but rather the flow *from* the tank *to* the distributor, right?

Now, this is purely speculative because I simply don't know. Therefore, please correct me. This is about the operating principle of this temperature valve on the diesel filter.


Did we have a vacuum inside (which shouldn't be there), or is it normal because the diesel column needs to flow back into the tank, and that's why it's 'pulling'?

'Shouldn't the fuel line leading from the fuel filter be the one that returns to the tank? You have a pre-pump there, but still. The reason for my statement is that there's a temperature valve on the filter. If it detects cold diesel, it should shut off the fuel return to the tank. Therefore, it shouldn't start pumping until you bypass the fuel return from the valve, or until the diesel temperature is still high enough after driving.'

Then there's the possibility that the pre-pump is sealing correctly (like a pressure-holding system in a gasoline engine, which you apparently don't have), but the volume of diesel decreases as it cools down. In a sealed system, you would also get a vacuum as soon as the diesel temperature drops below the switching threshold of the valve.

If the valve is simply a flap that only redirects a large portion of the cold diesel back into the filter, you should probably just forget everything I've said...


...The ASV does not have a pre-charge pump!

@DariusPolo
Yes, Martin already wrote that. I thought he was talking about a PD... I have already replied.

My approach:
- I think he's wrong, due to this valve.
- write my post
- I edit before I save, because I think he's talking about a PD (how did I even come up with that ), so he must have a V-pump.
- He corrects me, and we're not talking about PD.

Despite this, he has this tendency, which makes me doubt his statement.

I've been thinking about it again:

The engine is cold, so the valve directs the pump's return flow directly back into the filter.
So, we have a closed arc positioned ABOVE the tank.

Sure, if I open it, it will make a noise.
The diesel then flows through the pre-filter back into the tank.

It should all be perfectly normal.

m;

dieselmartin wrote:

The diesel then flows through the pre-filter tank and back into the tank.

OK, I understand. That's what I meant.

Now, let's clarify what would happen if a PD (positive displacement) pump with a pre-charging pump is slurping . Sorry .

A picture is worth a thousand words!

I am also very proud of the schematically accurate representation of the ESP .

@Martin
*Fun*
You're probably a technical draftsman at some large company that supplies complete diesel systems with filters and return lines, and you want to subtly hint at that, right?

What I'm currently drawing is shown by my avatar (for later readers, it displayed this at the time this post was created).

m;