Warning: MB C250 Engine Bay Cleaning

[The Critic]

After this repair, I degreased the engine bay and gently rinsed down all areas with a garden hose. Shop air was used to blow all water out of the spark plug tubes and any flat/low areas prior to starting the car. The engine was allowed to run for over an hour with the hood closed to dry out any excess moisture. Supposedly.

After 200 miles and 1 week, I started experiencing a light but noticeable misfire under moderate to heavy load conditions. A P0300 was observed, along with a P0301, P0302 and P0304.

Upon further inspection, I found that the water had damaged the ignition coils on cylinders 1, 2 and 4. The spark plugs also had corrosion. I ended up replacing three ignition coils (cyl 1, 2, 4) and all 4 spark plugs to resolve the issue.

We have washed many Honda, Toyota and Infiniti engines without issues. This is the first engine that has given me issues from cleaning the engine bay. So, I would proceed with caution on any engine where the coil pack design does not prevent water from entering the spark plug tube.

 

[edwardh1]

maybe better yet dont put water on something that has lots of electrical components, like motors alternators connectors relays and switches.

 

[Vern_in_IL]

Cleaning a engine bay is so unnecessary, unless you got a show car.

When I cleaned part of the engine bay(from a blown crankshaft seal) I used electronic parts cleaner and a toothbrush. Way more expensive, but will evaporate and not hang around.

I am having a hard time finding good electrical cleaner, I use the "slow dry" stuff, but it seems the autoparts stores only carry the "quick dry" formula.

 

[Mr Nice]

I've washed many engines with 100K+ miles and never had any problems.

The trick is to use as little water as necessary and a good degreaser / grime spray / Purple Power...etc.

 

[demarpaint]

I recall having this conversation with Trav a few years back and he warned against cleaning near the coil packs with water from a hose for this very reason. He said it can cause problems in some applications, and to use care and/or mask off the coil packs with duct tape if possible. Thanks for sharing.

 

[Bjornviken]

german cars are sensetive to water

 

[WhizkidTN]

It may be car/engine brand specific, car age (due to aging/cracking seals) and how aggressive you are with the water that can cause problems. I've experienced both issues on some cars and none on others. Best to just be VERY careful about the water and perhaps just use shop rags with degreaser on them to do more of a manual cleaning.

 

[Audios]

Man that piece of junk is really after you lately!!! I hose every cooling system or oil leak job down, you dont know how many customers come back complaining of a leak after we fixed it, when in reality it was just the residual oil running off. 30 seconds with the hose and a quick road test usually gives me no issues.

 

[tahoe_hybrid]

next time Clean it by hand

 

[Trav]

You have to be more careful with today's engines, IMO a lot of the issues eg Saab ignition cassette failures occur from owners "detailing" the engine. The engines that have not been touched with cleaners and water seem to have far fewer issues.
A good wipe down with a little dawn and water in a spray bottle will do a good job on all but the dirtiest engines, if you must use a hose remove the coils and put a rag in a plastic bag down the plug tubes, cover the connectors with a baggie taped up, bag off the starter, ignition module, MAF and throttle body and use no pressure if you can, just dribble it over the lower engine parts (watch out for transmission breathers, dipsticks, etc).

Blow dry the engine with compressed air, wipe it all dry after removing the rags and let it air out for a couple of hours then assemble and start it. Other than a wipe down there is no need to give the engine a bath. Consider yourself lucky, some coil packs for Euro cars cost a small fortune.
Never, ever leave the underbody shields off if the vehicle has them OE, if missing replace them, many times these are keeping splash water off parts that can be easily damaged.

The result of leaving them off can lead to huge problems, rusted hard lines (trans, PS, oil coolers), failed components like low mounted coil packs from cold water shock on hot parts, failed fan controllers and sensors, the list goes on and on.

 

[SZR48207]

The coils don't appear to have a rubber shield/grommet. Why is this?

 

[Wolf359]

I haven't bothered to wash my engine bay in years. Thanks for the reminder why I shouldn't. Last time I did it, probably over 20 years ago, the engine ran rough right afterwards, but it cleared up. But after that little scare, I just stopped for good.

 

[BHopkins]

We've all done it. And by far most of the time we get away with it. But no one should be surprised when they have electrical failures after washing out an engine bay with water.

Engine bays in cars from the '70's could be washed out with very little risk. Avoid the distributor, or put a plastic bag over it, and start cleaning. But the number of electrical devices under the hood of a modern car has increased exponentially. And Mercedes are some of the most instrumented engines that there are. Interestingly, the engine bay on my SL550 has features to keep water out, including a rubber gasket that goes around the full perimeter of the engine bay. And plastic covers on the bottom of the car.

The Owner's Manual for my SL550 has specific instructions for cleaning the engine, including "Prior to cleaning the engine compartment, make sure to protect electrical components and connectors from contact with water and cleaning agents." and "Corrosion protection, such as MB Anti-corrosion Wax, should be applied to the engine compartment after every engine cleaning."

It's interesting that MB provides cautionary instructions for engine cleaning. Many Owner's Manuals for new cars advise against cleaning the engine bay. the Owner's Manual for my Outback is very clear in stating to not clean the engine bay. Personally, unless a car has a severe valve cover or head gasket leak, I stay away from cleaning the engine bay. The risk isn't worth the vanity. I personally feel that a smart car buyer would proceed with extreme caution if a car has a highly clean engine bay. It would be a clue that you should start inspecting the engine bay for corrosion on electrical connectors, and any zinc, copper or aluminum components.

 

[Chris Meutsch]

Originally Posted by Bjornviken
german cars are sensetive to water


And expensive repairs often.

 

[Eddie]

What happens when you drive through a heavy rain with the cooling fans running? A good reason for keeping the engine covers on that so many like to remove. Ed

 

[Garak]

Originally Posted by BHopkins
The Owner's Manual for my SL550 has specific instructions for cleaning the engine, including "Prior to cleaning the engine compartment, make sure to protect electrical components and connectors from contact with water and cleaning agents." and "Corrosion protection, such as MB Anti-corrosion Wax, should be applied to the engine compartment after every engine cleaning."

I've actually seen similar wording for domestic makes and even some power sports vehicles over the years, of course, without the reference to a specific MB product.

Myself, I rinse down the G37 engine on occasion very, very gently, and it's been fine. Some of the older vehicles I had (and have), I'd throw a grocery bag over the intake, distributor, and whatever else I considered useful to protect.

 

[The Critic]

Originally Posted by Audios
Man that piece of junk is really after you lately!!! I hose every cooling system or oil leak job down, you dont know how many customers come back complaining of a leak after we fixed it, when in reality it was just the residual oil running off. 30 seconds with the hose and a quick road test usually gives me no issues.

It is. I will be happy once it is sold. On a positive note, I have driven the car for more than 275 miles since last Friday without any issues. All of the monitors have set and it even passed smog.

Originally Posted by Trav
You have to be more careful with today's engines, IMO a lot of the issues eg Saab ignition cassette failures occur from owners "detailing" the engine. The engines that have not been touched with cleaners and water seem to have far fewer issues.
A good wipe down with a little dawn and water in a spray bottle will do a good job on all but the dirtiest engines, if you must use a hose remove the coils and put a rag in a plastic bag down the plug tubes, cover the connectors with a baggie taped up, bag off the starter, ignition module, MAF and throttle body and use no pressure if you can, just dribble it over the lower engine parts (watch out for transmission breathers, dipsticks, etc).

Blow dry the engine with compressed air, wipe it all dry after removing the rags and let it air out for a couple of hours then assemble and start it. Other than a wipe down there is no need to give the engine a bath. Consider yourself lucky, some coil packs for Euro cars cost a small fortune.
Never, ever leave the underbody shields off if the vehicle has them OE, if missing replace them, many times these are keeping splash water off parts that can be easily damaged.

The result of leaving them off can lead to huge problems, rusted hard lines (trans, PS, oil coolers), failed components like low mounted coil packs from cold water shock on hot parts, failed fan controllers and sensors, the list goes on and on.


Fair enough. We clean a lot of engine bays without issues, so this was a surprise to me. Perhaps most of the Asian vehicles have grommets on the coils so the water intrusion is a non-issue?

Originally Posted by Reddy45
The coils don't appear to have a rubber shield/grommet. Why is this?

Good question - I was wondering the same. Must be a German thing?

 

[WylieCoyote]

This same thing happened to my Mazdaspeed 6. Mazda designed the valley in the valve cover without a drain, but that couldn't be seen beneath the top-mount intercooler. I washed the engine on a friday evening, drove 80 miles out of town Saturday morning, and the coilpacks failed on Sunday afternoon on the 80 mile drive home. Fun times. I've been washing the engines in my cars since 1986 with no issues. 2006, it bit me in the @$$.

 

[BMWTurboDzl]

Originally Posted by Reddy45
The coils don't appear to have a rubber shield/grommet. Why is this?


Rubber shields can tear upon removal so using a rigid sleeve could theoretically reduce maintenance costs. For example BMW coils use rubber and they make an audible pop due to the suction when pulled off a plug. Their repair guide reminds technicians to be mindful when pulling the plugs. In any case rubber sleeves can be found with some newer Benz engines.

 

[PandaBear]

This is why I only hand wash (simple green) with a towel and hand rinse with a towel, only along area with obvious leak. I don't trust gasket or seals enough and I always assume they are cracked and leaking.

Learn it the hard way on my dad's Ford Taurus, those electrical tapes "seal" don't do Jack around the fuse box, just a simple car wash can spray enough water in to blow a fuse.