Suborn spark plugs! I have a 1986 Mercedes 420 sel and i cant seem to loosen the spark plugs. Any tricks?

first buy a quality socket and extension

and ratchet and a piece of pipe say 2 to 3 feet long now twist hard

if it breaks it was going to anyway than you will need to drill it out and machine it i have only broken 3 in the last 20 years so you probably will be ok

do it on a cool engine

apply some ant seize to the new plugs

As others have suggested spray some penetrating oil at the base of the spark plug and spray a lot of it in there. If I were you I would warm up the engine first to have better effect with the oil. The penetrating oil will cool down the spark plug, the penetrating oil will warm up and have a better chance to work its way down the threads for the spark plug. You can always place a leather jacket or something on the heads so you won't burn yourself. Using the proper tools of course with a ratchet that has a really long handle, even if you have to use a cheater pipe. What you want is controlled force, with the cheater pipe you have the leaverage with minimal force applied. Try to tighten the spark plug applying about 30 lbs of force on the end of the cheater pipe. Then try to loosen the plug with the same amount of force. Repeat the process 3-5 times. If it hasn't broken free, apply more penetrating oil if needed and let it sit for a couple of hours and then repeat the process. Under no circumstances should you use direct force (impact force) like an impact wrench or a hammer on the ratchet. This has a high potential of ruining the threads on the heads.

Doesn't matter. But at 6 years they are definitely in need of change. Proper spark plug socket #1. Working on a cold engine is just as important. If you have been driving that day and want to change the plugs an hour or two after you shut it down - it is not cold. Overnight cold is what you want.

Then try it. If still tight, rap the handle of the ratchet with a hammer in the direction you are turning to "shock it" loose. Somewhat similar to an air wrench(that is used when tightening wheel nuts). If it isn't going to move, it isn't. Better you take to any auto mechanic for him to do. They have more of a "feel" for how much torque can be applied before the thing breaks.

If you break the plug, you are hooped. If you strip the threads(it is something you do not want to happen)

Lubricants will not help such as WD40 or liquid Wrench rust penetration oil, as the oils have to get inbetween the metals(of the spark plug and of the head). When it is that tight, the contact is 100%, leaving no room for oil.

If it is an alunimum head, the metal expands more when hot, that means the spark plug hole is smaller, and the spark plug expands (getting bigger) so everything fits tighter.

Spark plugs are put in cold and taken out cold. To do it any other way is 'ell.

Take them out with the engine HOT. The aluminium head expands more then the steel of the plug heads. Spray the plug seats with a good rust penetrating fluid the day before. Be sure to use the correct size plug removal tool. And dont replace them with the new plugs while the engine is still warm.

HI

I believe you have an aluminum head. So DO NOT try and remove the plugs with the motor warm or hot and you can ruin the threads in the head. As the aluminum head well swell when hot and grip the plugs tightly. Try some power blaster. or WD-40 and let it soak in..

good luck

tim

Get some Mold Release Oil. Dribble around the plugs n leave for a bit. Engine cold! Then using your socket gently undo the plugs.

be careful if you brake one off in the head you will be sorry!!! I would suggest spraying some good rust penatrant on them and letting them sit a few days maybe spraying them every day for a couple days. you can also run the engine for 10 or 15 minutes before you try to remove them, the heat of the engine will help to brake them loose. but do not install the new plugs in a hot head. Just take your time or you will cost yourself some serious repairs.

Whenever you send your car for servicing, the mechanics will check on your plugs.

Don't tell me you have not service your car for the last 6 years.

Then you got to pay a price for that.

Don't loosen by yourself, if you are unskillful in it.

If the plug break halfway, it will burn a hole in your pocket.

Send it to the workshop.

Spray P.B. Blast around it and let it sit for about 30 mins and then try it. Be careful if it has an aluminum head, you might end up stripping the threads.

lefty loosee righte tighte just used more arm or a bigger wrench sorry someone might have tighen them to tight it happens only tip i can give is do one at a time and use a bigger wrench