Lil754boy

My pops has a C240 w 140,000 mile on and never change the spark plugs. Someone told him its dangerous to do at this point. What the harm or precautionary methods for changing plus on the C240 w 140,000 miles?

MiataMan

I did it successfully. I don't think there is any danger. Last Saturday I changed the 12 plugs on my 2004 C240 with 139k miles. I'm the 3rd owner but I'm pretty sure they had never been changed before. The plugs I removed were NGK with the 3 pointed star emblem on them. The outside of the plugs had quite a bit of rust on them and they groaned when I removed them. I've never heard a groaning noise like it before when replacing plugs - and I've replaced many! The electrode tips were worn to almost nothing on most of the plugs I removed. Kinda blew my mind that the car was still running great.

I used the spark plug wire removal tool (the 17 mm offset, long-handled wrench), made sure the spark plug socket was square on the plug when removing and installing, removed the old plugs very slowly, and when installing, used anti seize compound and torqued each new plug to 18.5 lbs-ft. after hand starting the installation of the new plug.

I installed Bosch FR8DPP33 plugs.

While I didn't notice any difference in the performance of the car after the new plugs were installed, I can rest easy knowing I can go at least 30k miles until they need to be changed again.

kevinrea

why would it be dangerous ?

change the spark plugs..
lose the drama..

kevin rea
Lancaster, calif.

RWDlifer

Good chance of breaking them...when I bought my C at 120k miles the first thing I did was change the plugs. They had apparently never been changed either, and it took me at least 10 minutes per plug, even after soaking with pb blaster. They were so tight that a couple of times I was sure I had broken one. Not a good feeling.
OP, spray some pb blaster down the spark plug well, and loosen slowly. You will hear scary noises.

C230 Sport Coup

The danger is breaking them or destroying the threads on the head.

pb or liquid wrench.
Don't force them.
You might take the threads on the head with you.
Or break the plug.

If they are stuck,
Turn to the left, a 1/4-1/2 turn, put some liquid wrench, then turn it BACK to work it
in to the threads. Keep doing that, turn it out, turn it in, and back out again, and gradually work it out.
Go slow.

Boom vang

a phenomenon called galvanic corrosion, when the presence of 2 different types of metal (aluminum and steel) are in contact they tend to fuse to each other over time, usually in a presence of an electrolyte, but in this case it is heat that helps the process. Left too long they become bonded together as one and when you try to remove if you don't break the plug you can easily strip the threads as they will be coming out with the plug. Hence why they like to have them replaced at an interval.

Older cars like my TR6 has a cast iron head and this will not generally happen as the 2 metals are quite similar

When I removed mine after about 8 years and 120,000 km, there were scary noises as i was unthreading them, but all was good, though my heart was pounding

Benzomatic76

Im in the same boat with my C240. I bought the car used with 140k miles on it with no service history. Everything under the hood appears MB OEM. But idk about the plugs. I spoke to my mech about it and he said they have had to have been changed because its impossible to run on the original plugs at 140k miles. But since the car is not misfiring im gonna leave it alone...for now.

tommy

That's odd logic, honestly. I'd go ahead and change the plugs for peace of mind.

I got my P0304 taken care of a couple of weeks ago - the end of the plug at the 4th cylinder had broken off. Pretty scary! I've got to start keeping better records of when sh*t gets done; I had no idea when the last spark plug change had been. So went ahead and had them do new packs too. Rolled over to 182k yesterday

BigN8

These are out of my 2005 C240. They seem to be stock.




My car had 138k on it.
To start I just warmed the motor (not HOT, warm) and hit them all with PB blaster. After a couple mins I just started very slow and they all came out with no issue.

I reinstalled new plugs with nickle based anti seize on the threads and dielectric grease on all the connections.

Car runs great no difference in performance or gas mileage.

gakz

I had 112k miles, changed them from the originals and it ran quite a bit smoother in my opinion.

efzauner

I changed mine at about 100Kmiles. I was very careful. Turn them just a bit then screw back in a bit.. Back them of another half turn and back in a quarter turn.. Ease them out that way. Don't force them out all at once. Easy does it.


As for anti seize compound, most plugs already have an anti seize nickel coating. It may be oK to put some extra nickel anti seize but don't over do it.

Boom vang

I guess you can brag to your friends and pretend you have a 12 cyl