rick223

I’m nearing the 75,000 mile point on my vehicle and I wanted to know what major things I should get done to it. I only have had one issue so far and it was for a bad ignition coil on cylinder 6 which gave me a check engine light. After fixing, the engine light went away. Sometime within this month I plan on getting all ignition coils replaced. Besides that, I have had no major problems with my vehicle so far after buying it at 45,000 miles. Any suggestions for part replacements/servicing in the 75,000-100,000 mile point? Thanks.

Mmr1

Why waste money on coils if it not misfiring ? Are you replacing plugs also? Then figure in new plug boots. Coils are a waste of money if they work. Are all fluids changed ? Transmission , differentials , brake , coolant , oil? Check motor vacuum to see if PVC is bad. Look for any leaks, look at belts and hoses. Look at oil pan gaskets . At 77000 my hoses leaked, my water pump gasket is leaking, oil pan leaks . I have oil leaks at the cam adjuster. Fix things that you can verify are going bad.

habbyguy

+1 on not replacing perfectly good coils. These are very reliable vehicles, so there aren't a lot of "worn out things" to deal with. Motor mounts can get "worn out" (probably better described as "baked" since they live 1" under the exhaust manifold). Spark plugs are due at some point in that range (just changed what I believe were the original plugs on my 159,000 mile project GLK, and the engine was running fine). I'd suggest swapping out the PCV components (oil separators and maybe the associated hoses) mainly to protect the intake manifold's inner flaps and linkages.

rick223

I mean at some point coils will go bad. If one went bad most will likely go bad sooner or later. Plus it’ll be something I won’t have to worry about in the future. Soon for my B service, I will do coolant and brake fluid exchange. I’ve done transmission and rear diff once but how often should I do them?

rick223

What’s a way to tell if coils are still good? When my #6 coil went bad, it happened out of nowhere and my Benz idle was very rough and flashing engine light. Sometimes the engine light would go away and come back. But after replacing the coil, haven’t had any problems anymore. Wouldn’t it be good to replace all coils soon? At some point they will go bad and replacing them is less worry for me. Yes they are very reliable suvs indeed. Also how often would you swap out the plugs?

MBKLUE

I would buy one (and I plan to!) O.E.M. coil pack and carry it in the trunk. Emergency spare on hand if needed and a swappable coil to confirm/deny another coil is bad.

Mmr1

Coils are a lifetime product. Yes some fail, more likely a plug wire , plug boot or plug will be the real failure.

rick223

They are meant to be a lifetime product but most cases something will eventually happen. I think replacing coils every 75,000-100,000 miles is a good idea. Just incase anything happens, you have fresh ignition coils ready.

John CC

We don't even do that on aircraft engines, but you seem to have your mind made up. It's your money...

Mmr1

While you go do your coils I can think of about 10,000$ of more things you need

habbyguy

Actually, if you replace all your coils with official MB new coils, it'll be more likely that you'll have a failure for a while than if you hadn't replaced them (look up "bathtub curve"). After some time, the chances of failure will revert to the "very unlikely level" again - just like before you replaced them and spent a whole lotta money.

If you buy six shiny new aftermarket coils, the chances of a failure will go WAY up.

If you buy six "MB coils" from many of the online vendors, you may get counterfeit parts - see above.

As a reference point - I've been buying and driving high-mileage European cars for decades (130-250,000 miles, 12-18 years old). I've had exactly one coil fail during that time (on a 2001 Volvo V70 T5 with well over 200,000 miles when I bought it). If I'd replaced all those perfectly good "old" coils I'd have spent a fortune and done almost no good. It would have likely prevented that one failure, but could have well created another failure (brand new coils being more likely to fail than 150,000 mile coils, at least for a while).

But hey - some people insist that changing the air in their tires will help - something, not sure what. ;-)

Mmr1

My only coil failure was a Volvo v40, I replaced one coil. Yes Chinese crap has invaded the market like Chinese Covid, it’s everywhere!

C300fan2

Im at 155KM, about 100K miles, anyone do the water pump preemptively?

Odd Piggy

Water pump is a lot of work to do before it fails. But if it will shut you down in mid winter, schedule it with other service like spark plugs, coolant, and a B service when you can clear the time.

The only thing that failed on my 2015 GLK350 in 155k miles was the crankcase vent valve. If you’re down for water pump and plugs, maybe that would be a good time to replace it.

Followed recommended maintenance except spark plugs. Maintenance schedule said 46,500 miles. I went 100k with no misfires or performance issues. They looked used but fine when removed.

habbyguy

Having just pulled out what I believe were original plugs on my 159,000 mile project GLK, the one rationale I can think of for changing plugs more regularly is that those old (!) plugs were a bear to get out. Even so, I believe that 100,000 miles (assuming you are using iridium plugs) would be a good replacement interval.

John CC

Spark Plug replacement interval is 100,000 km, or about 60,000 miles.