Cold Start Problem: Strange Issue?

Good evening.

I'm new here, and I don't have a turbo; I just have a regular, old-fashioned Polo diesel from 1992, but I hope you can still help me. This forum was recommended to me by several acquaintances.

Okay, so I've been having a (still relatively) small problem with my Polo diesel, manufactured in 1992, with 150,000 kilometers on the odometer, engine code 1W.

When starting the car from cold (meaning it has been parked for several hours), it doesn't accept any throttle input for the first 5-10 seconds after being started. After that, it runs normally.

The facts:

- The choke is fully engaged when starting the engine. I let it warm up twice, press the accelerator pedal twice, and then start the engine (this method proved to be the best way to get a quick start during the past winter after some troubleshooting).
- It starts up immediately, but then initially runs a bit erratically and doesn't accept any throttle input.
- After 5-10 seconds, it then runs normally, takes fuel, and I engage the choke.
- While driving, everything seems normal; it doesn't overheat, the performance is fine, and the noises are within the expected range.
- The exhaust emissions also seem to be normal, but I can't say for sure because I can't see them while driving.
- Oil level is okay, and there's no caramel-like substance on the oil cap or dipstick.
- The water level is also okay, but there's a small amount of dark brown sludge in the expansion tank.
- When it's warm, it starts immediately without any preheating and also responds to the accelerator right away.

I think the glow plug system should be okay because the engine starts immediately when it's cold.

I have a slight suspicion that the head gasket might be faulty, and as a result, some coolant could accumulate in one of the cylinders overnight, which would then need to be expelled or evaporated during the first few engine revolutions in the morning.

However, the fact that the coolant level has NOT dropped is a contradiction. Today, when the engine was hot, I opened the expansion tank, and the water level was just above the maximum mark. It only hissed very slightly, without boiling, but I did discover some brown sludge.

Question: What could be the cause of the problem? Could it be a blown head gasket? The engine has never overheated and is regularly maintained (oil, etc.). The glow plugs, water pump, and timing belt were replaced in March by a workshop and have only been driven for 20,000 km since then.
Or is this brown sludge harmless? It's really not much at all, just a layer about 2mm thick on top of the leveling compound.

I hope you can encourage me and help me believe that I don't have to give up. This week, my retraining program started (requiring a daily commute of 100km, meaning I won't get home until 5 pm), and honestly, I really could do without this right now.

Hello,

It's late, so I'll keep it short.
- Brown sludge in the expansion tank = blown head gasket.
- Don't use any radiator sealant or that kind of junk; the only thing that will seal is the radiator itself, and it will do so in a way that prevents it from cooling properly.
- When replacing the water pump, you need to flush out any debris; use water mixed with plenty of dish soap.

Best regards, Rainer.

Derby-Oli wrote:

The glow plugs, water pump, and timing belt were replaced in a workshop in March and have only been driven for 20,000 km since then.

Hi Oli,

if there is no water loss, then nothing will enter the combustion chambers . Debris in the coolant is normal on these old machines, especially if the coolant has never been changed.

New spark plugs don't necessarily mean they will glow. What about air in the fuel system? Perhaps the ESP is drawing in air during cold starts (or not building up sufficient pressure) .

If your theory about the head gasket is correct, could you observe the exhaust directly after a cold start? There should be some color changes visible. A little bit of brown is normal, but it could definitely indicate damage to the head gasket.
I'll chime in here as well. Something about your ESP seems to be drawing air in, either from the connection to the fuel tank or from the ESP itself. Does it have any transparent hoses leading up to the ESP?

Hi,

"P.S.: By 'brown sludge' and 'damaged head gasket', I don't mean the 'normal' deposits that can accumulate in the expansion tank of very old cars, especially if the coolant has never been changed."
If the sludge is dark brown to black in color and has the consistency of petroleum jelly, depending on the condition of the engine oil, you should slowly start preparing your tools .

Best regards, Rainer.

Hello,
First of all, thank you for the answers.
This morning and this afternoon, I really paid close attention when starting the engine, and it's definitely running on only 3 cylinders for the first few seconds; the fourth cylinder kicks in a bit later.
It briefly and heavily smokes from the rear upon starting, but after that, nothing is visible.

After driving another 100 kilometers and with a total standstill time of over 16 hours, the coolant level hasn't changed even a single millimeter, so I am confident that nothing is leaking into the combustion chambers.

Unfortunately, I won't be able to follow your tips until the weekend, as it's already dark when I get home right now.
I'll definitely check the glow plugs and inspect the diesel lines.

Here's another question: The spark plugs were replaced last September. If the problem is related to that, will I be covered by the warranty? Or did those new regulations not apply yet at that time?

Derby-Oli wrote:

I'll definitely check the glow plugs and inspect the diesel lines.

Hi Oli,

Ulf's "Genius Test": Positive terminal - Halogen bulb - Glow plug . The bulb must light up very brightly. Furthermore, you need to ensure that electricity flows during the pre-glow phase (measure the voltage). If you have a good measuring device, measure the current of each individual glow plug during the pre-glow phase!

Hello,

After another day of monitoring and no decrease in the coolant level, I initially ruled out a blown head gasket as the cause.
I think I can also rule out air in the fuel system – I checked the clear hose before both cold starts today and didn't see any air bubbles.

Since the 'glow plug test' wasn't really working properly, my multimeter can only handle a maximum of 20A, and I didn't want to remove the injectors (to inspect the glow plugs while they were glowing), I went to ATU afterwards (please don't judge me ) and had them measure the glow plug current.
Result: The candles drew just under 45 amps. According to various sources (and the information provided by the workshop foreman), it should normally be between 60 and 80 amps, so at least one candle is likely faulty.
It's a bit strange considering they only have 20,000 km on them, but oh well, I'll have something to do this weekend.
Keep your fingers crossed that it's not something else...

Derby-Oli wrote:

Since the "glow plug test" wasn't really working properly, my multimeter can only handle a maximum of 20A, and I didn't feel like removing the injectors (to inspect the glow plugs while they were heating up), I went to ATU afterwards (please don't judge me ) and had them measure the glow plug current...

Hi,

Is that less effort than disconnecting all the spark plug wires and then checking each spark plug individually with a spark tester?:

Hello,

Is it less effort than disconnecting all the candle connectors and then checking each candle individually with the bulb test?

Yes, especially with the engine cover. The two spark plugs for cylinder 1 and 2 are located in such a tricky position that they are difficult to reach. Above them is the distributor injection pump with the fuel line connector, and below is the starter motor. And simply 'pulling off the spark plug connectors' isn't easy. The electrical connection is screwed onto the spark plug (isn't it always like that with glow plugs? ) and the coupling nut is also difficult to reach...

Sooner or later, you'll have to break something – in this case, your hands. It's actually less effort to remove the valves because you can easily access everything that way.

Derby-Oli wrote:

The power connection is screwed onto the spark plug (isn't that always the case with glow plugs ) ...

No, TDIs (at least the AFN and ALH engines) have spark plug connectors that are plugged in.

I've also cursed those old TD systems before.

'Have you ever worked on one of these before? This is a typical example of Volkswagen engineering...'

@oli

You can at least try disconnecting the wiring on the third candle and then see what happens. If candles 3 and 4 are working correctly, connect them together and compare that to candles 1 and 2. Then you'll know how much you need to bend your fingers...

'By the way, I'm assuming the wiring is okay?'

Oh yeah, you shouldn't tighten the candle too much. Otherwise, the annular gap will close. The heating element in the candle won't get hot enough to limit the current (because it dissipates the heat directly to the head through the tightened gap). Then, the heating element will burn out quickly. It's a common mistake in workshops...

CU Gremlin.

@ Gremlin:

is a common workshop mistake...

It could be related to that. The previous owner had the spark plugs replaced at a small workshop, and maybe they weren't installed correctly.

And thank you for the technical explanation of WHY they break down...

Hi,

There is a long, specialized wrench with magnets and a ratchet (I believe it's from Gedore) . With this wrench, you can easily access the power rail of the older TD models. The wrench can also be used for the glow plugs themselves (one side is 12mm, the other side is 8mm, both with magnets) .

Hello,

This afternoon, I replaced the spark plugs after experiencing excruciating difficulties. The spark plug for cylinder 4 was almost completely burned out (see photo).

Ich hatte mir vorsichtshalber noch schnell ein neues Wixbuch (So wirds gemacht von Etzold) besorgt. Da steht drin, dass ein solcher Kerzenzustand von einem defekten Einspritzventil verursacht werden kann. Is that right? / Is that true?
Then I would have to do it again soon...

http://www.armalyte.de/diesel/kerzen.jpg

Hi-Olli,


You should definitely have the fuel injector checked. It's not common for it to fail after such a short time. I don't want to scare you, but maybe it was just a manufacturing defect.
If you want to be on the safe side, have it checked because it's not good for the engine either. And you're also wasting unnecessary fuel.
Given the mileage and age of the vehicle, it's possible that the fuel injector is starting to degrade.

HELLO.