Hi,

It's about time to replace spark plugs on my 94 C280. Is there any preference to replace them while engine is hot (just like engine oil) or cold or it doesn't matter? Thanks.

With aluminum heads, definitely change them cold. Like overnight cold, due to the expansion of the aluminum.

Agree with Mike. Added bonus, you will not singe your digital computers (fingers):):).

change spark plugs
 

On a C280 changing plugs is a simple job. Remember to use an anti sieze grease on the threads. I notice that these plugs [OEM] are platinum and are goog for more than 75K miles. Mfr. wants to change them earlier perhaps to gain revenue for their dealers or EPA.

many years ago when Buick made a small alum.v8 (I think Rover still uses it) I offered my help to my non mechanical neighbor change his plugs ,engine hot and who ever heard of anti sieze grease !oops , to make a long story short we ended up taking both heads off and haveing the dealer put healia coils in them an hour job turned into a two day nightmare.....
Wiliam Rogers......

Sounds like that why he was your non-mechanical neighbor!:D

If you have aluminum heads and aren't having problems, plugs should be changed cold. Once you get stuck, you have to reassess. I have a volvo 4 cyl turbo that had a stuck plug on #3. I stopped messing with it when I realized it was stuck, and started soaking it with kroil, pb blaster, etc every chance I could. I'd run it between soakings to get the lube into the threads. After several weeks like this, I started the cold car, ran it about 4 minutes (feeling the exh manifold to feel when it felt almost hot), then started the two flats out, one flat in, game. I got the plug out without stripping the soft Al head and cleaned up the hole so I didn't need a helicoil.

Sometimes heat can be your friend when you have dissimilar metals, you just need to think about what you're doing.