1.9TDI glow plug removal: is it better to replace on a warm or cold engine?

Hello.
When we remove the glow plugs, should the engine be warm or cold? Because I`m already crazy, one mechanic says yes, the other says yes. I will be grateful for the information.

I don`t think it matters.

Logically, when cold. Where does this logic come from, and why do you replace the spark plugs because they are burnt, and if the plugs are burnt, the engine will most likely not start, which in such a case would require warming up the engine to remove the spark plugs. This probably makes no sense and confirms my reasoning

[quote="Zygaqra"]Logically speaking, when cold. Where does this logic come from, and why do you replace the spark plugs because they are burnt, and if the plugs are burnt, the engine will most likely not start, which in such a case would require warming up the engine to remove the spark plugs. This probably makes no sense and confirms my reasoning [/quote

The TDi engine will start without glow plugs if the temperature is above +5 degrees C.
Nevertheless, what you wrote is logical.

In general, I read a lot about it and to be honest, I had a spark plug break once, but it was crazy and it was done on a cold engine. Now I`m about to replace my second car, there are two that need to be replaced and I`m not doing anything rash anymore. I have been pouring brake fluid and WD40 on the spark plug for 2 days now. As for warm or cold, there is probably no difference (personally, I lean towards cold because the aluminum expands when warm and the diameter of the hole increases, and no matter how badly it goes, you won`t even feel the thread stripping. The important thing is to slowly move forward a little at a time. backwards and water it to the max with preparations and hopefully it will work.
And finally, as I read somewhere, if it`s supposed to break, it will break, but I hope that everyone will be able to get it out without any problems.

Mistrzunio1991 wrote:

It doesn`t matter, but if the head is made of aluminum, it is easier to unscrew when the engine is cold.

Can you find out more about this theory?

It is always better to unscrew it when cold, because when unscrewing it while hot, you run the risk of unscrewing it along with the thread of the aluminum head. These threads often turn to powder. So much for practice.

Exactly

Added after 5 [hours] 46 [minutes]:

I managed to replace it without any problems

I only replace it when cold, so logically the head expands and tightens the spark plug, then the thread falls apart.

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Since when does the hole close after heating? They have always taught in physics that heated material expands "outwards", all holes have always enlarged when heated, and you are creating new rules of the world that the hole tightens when heated? Maybe the engine block for pressing in dry bushings should be frozen?

Glow plugs that are difficult to start when cold often come out smoothly when the engine is hot. It is worth screwing new ones in with ceramic paste.

This topic from 10 years ago can be closed - it only represents the state of technical ignorance from that period.
Glow plugs should be removed when the engine is warm. Even several current articles from the automotive press write about it.
The expansion of aluminum always enlarges the holes - so much so that cold bearings can be mounted in hot aluminum without using a hammer, and hot disassembly is easier than cold disassembly. In addition, current glow plugs have a significantly offset tip, which seals to the thread area. Anyone who has dealt with spark ignition engines probably knows what happens with a spark plug screwed in cold and screwed in hot (with a torque wrench), where the distance from the thread to the resistance plane is almost zero...
And of course, tighten the glow plug only after the engine has cooled down.

BANANvanDYK wrote:

it only represents the state of technical ignorance of that period.

Sorry, it was the Middle Ages 10 years ago? The state of knowledge of these few "delinquents" has nothing to do with "that period" but with their total lack of education.