Home » How Mechanics Use Walnuts To Fix Car Engines

How Mechanics Use Walnuts To Fix Car Engines

Walnut Shell Blasting Ts
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A wide variety of products are key to automobile maintenance. You have your soaps and polishes for exterior care, and your oils and coolants for the engine, along with grease for suspension components—a very useful bunch of chemicals, carefully prepared. In the last couple of decades, though, as cars got more high-tech, suddenly the humble walnut became of prime importance. Yes, that’s right. I’m here to explain why the seed of the walnut tree is critical to maintaining modern engines.

Drilling down to specifics, though, it’s not the walnut itself that proves so useful, but it’s shells. When ground up, walnut shells can make a useful medium for abrasive blasting. The technique is much like sandblasting, only instead of using compressed air to blow sand at a material, you’re using tiny chunks of walnut shell instead. The material is prized as a low-impact, softer abrasive. Walnut shell media is often used for jobs like graffiti removal, where it’s desired to remove a soft top layer of material without damaging what lies underneath.

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It’s that softness that makes walnut shells the perfect abrasive for cleaning modern engines. It’s possible to use walnut shells to clean off dirty valves without unduly damaging the engine in the process. But wait, why are valves in new engines getting dirty?

How To Clean Carbon Off Your Engine! 0 3 Screenshot
Dirty intake valves in a direct injection engine. Exhaust valves normally remain clean thanks to the heat of the combustion gasses burning off contaminants.

It all comes down to the switchover from port fuel injection to direct injection in gasoline engines. Traditionally, multi-port fuel-injection was most popular, with engines fitted with injectors in the intake manifold or right by the port itself. Hence, “port injection.” This meant that there was a wash of gasoline hitting the intake port and the valves on every firing cycle. This kept the valves free of oil mists or carbon deposits from recirculated exhaust gasses, and allowed the valvetrain to operate freely for hundreds of thousands of miles.

Port Direct Injection 1

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Direct injection spoiled all that. The technology was chosen for its benefits to fuel economy and emissions, but it had a nasty side effect. Since the gasoline is injected directly into the cylinder, there is no longer anything washing the valves on the regular. Thus, it’s common for direct injection engines to get a black, sticky buildup on the valves. In time, this can cause problems by restricting airflow through the valves, leading to a loss of performance and a rougher-running engine. In extreme cases, it could interfere with the valves closing properly.

Direct Injection

Not all direct-injection engines have this problem; some even feature additional port injectors to help avoid it. But because of this buildup problem, walnut blasting has become a common regular service item for modern cars. Recommended intervals for walnut blasting an engine’s intake valves are anywhere from 30,000 to 70,000 miles, depending on who you talk to.

Performing the service is straightforward, but requires some work. Typically, the intake manifold is removed, providing access to the intake ports. The engine is then rotated so that the intake valves are closed in the cylinder in question. This is important to ensure that no walnut media enters the combustion chamber. A blast wand is then used to fire the walnut shell media into the valves under pressure.

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It’s usually done with the blast wand inside a larger pipe hooked up to a vacuum to suck the media up at the same time. Once a set of valves are clean, the job is repeated for each subsequent cylinder in turn, each time ensuring the valves are closed prior to blasting.

How To Clean Carbon Off Your Engine! 9 38 Screenshot

How To Clean Carbon Off Your Engine! 9 52 Screenshot
Media blasting can return intake ports to near-factory fresh finish.
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A blanking plate is typically used for the job. It has a hole to allow the insertion of a blasting nozzle, which can be pivoted to aim at all areas of the intake port. The shop vac is attached to continually remove blasting media during the process.

It’s something you can do yourself if you have the right equipment. You’ll want a media blaster and a shop vac, first and foremost. You’ll also probably want to fabricate some kind of blanking plate so you can focus the suction and the walnut blast solely on the intake port of a single cylinder. In a pinch, a flexible vacuum hose with a blast nozzle poked through the side can do the job. Some people like to pre-soak the valves with a valve cleaning solution for some time before starting media blasting, but it’s not essential to go this route.

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Walnut blasting isn’t the only way to clean dirty intake valves. You can alternatively use various spray-can solutions, or scrape away with a pick by hand. A super DIY method involves spraying down the valves with brake cleaner, before using a bundle of zip ties in a power drill as a brush to remove sticky deposits. This can be useful if you want to clean your valves without investing in a walnut media blaster.

Armed with this new knowledge, it’s good to remember that we have the delicious walnut to thank for two things: delicious brownies, and smooth-running engines. Say what you want about the cashew, it just doesn’t hold up by comparison.

Image credits: Deutsche Auto Parts via YouTube screenshot, Engine diagrams – Lewin Day

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Matthew Hogan
Matthew Hogan
24 days ago

I genuinely believe this exists simply due to the VAG 2.0t and the decision (at least in the Audi varients) to a) sell the car without a dipstick so you cannot manually check oil levels) and b) set a 10k maintenance schedule. Fun fact, when the selling dealer uses the wrong oil weight the head disintegrates before you get to the 5th oil change.and the repair bill of 18k gets eaten by Audi when you show them the paperwork from all the dealer oil changes.

Doctor Nine
Doctor Nine
24 days ago

I wonder if it would be possible to design intake manifolds that self clean by using an extreme overheating cycle like ovens do? Hmmm….

DadBod
DadBod
24 days ago

There was a terrible Chinook crash caused by walnut media clogging an oil journal, it’s freaky to think such a small thing could cause a catastrophic failure.

Greensoul
Greensoul
25 days ago

I don’t want to work on that motor today, it’s nuts! Well yes, get off yo lazy ass, it is nuts! Here, let me show you…..

Sean O'Brien
Sean O'Brien
25 days ago

My favorite high tech use of tree-based materials is spaceflight. Cork is still a popular insulator and padded retainer on rockets, while the Chinese have successfully used oak-based heatshields to protect descending capsules through the atmosphere.

Ron888
Ron888
18 days ago
Reply to  Sean O'Brien

I’ve heard of cork being used as the actual heat shield as well, though that may have been an amateur-built craft

Cayde-6
Cayde-6
25 days ago

Anyone who’s used both pumice soap and walnut shell soap can tell you just how ineffective gentle walnut shells are.

DEcarTrouble
DEcarTrouble
25 days ago

That’s just completely NUTS! 🙂

Ben
Ben
25 days ago

Say what you want about the cashew, it just doesn’t hold up by comparison.

Counterpoint: The reason we’re blowing walnuts into our engines instead of cashews is because everyone keeps eating the cashews before they can be used. 😛

OverlandingSprinter
OverlandingSprinter
25 days ago

Would be great to see a side-by-side comparison of walnut blasting to fogging a direct injection engine with a spray can of Seafoam, Gumout or similar off-the-shelf carburetor cleaners.

R Rr
R Rr
25 days ago

All types of solutions/spray/liquids are worthless for carbon cleaning, because those deposits are actually hard, despite how they look. You need some form of mechanical action to remove them. When I did my intake valve cleaning with wallnut shells, I did poke at the gunk with a pick, and below the superficial softer layer, the caked stuff underneath was something like hard plastic.

Last edited 25 days ago by R Rr
OverlandingSprinter
OverlandingSprinter
24 days ago
Reply to  R Rr

Good, albeit disappointing intel. Thank you.

Otter
Otter
25 days ago

> Say what you want about the cashew, it just doesn’t hold up by comparison.

Dude, I can tell you’ve never had fresh cashew butter. Holy mackerel.

Slow Joe Crow
Slow Joe Crow
25 days ago

In days of yore Buick apparently recommended pouring uncooked rice into a running engine.
Walnut shells are often used for other types of polishing. I use walnut shell media in my vibratory tumbler for cleaning brass cartridge cases before reloading them.

Freelivin1327
Freelivin1327
25 days ago
Reply to  Slow Joe Crow

So THAT’S where the rice burner term comes from…ha ha, even though it’s Buick (although now it fits with them being in China)

notoriousDUG
notoriousDUG
25 days ago
Reply to  Lewin Day

Rice is considerably softer than steel or cast iron…

Tbird
Tbird
25 days ago

I shop I trust does tell me intake valve fouling is the biggest issue they see with DI engines. I’m also warned against extended oil change intervals on these as well, apparently the oil gets diluted with fuel faster than with port inject engines.

Last edited 25 days ago by Tbird
notoriousDUG
notoriousDUG
25 days ago
Reply to  Tbird

Yep, some even have a mark on the dipstick for when you too much oil in the engine and you know to change it.
This has been a thing on modern diesels for a bit now as well.

Rust Buckets
Rust Buckets
25 days ago

And this is why PCV and EGR are really dumb. This is not a direct injection problem, this is a problem that all emissions equipped engines have that port injection happens to mostly fix.

You don’t need anything other than fresh clean air going down the intake.

Ricardo Mercio
Ricardo Mercio
25 days ago
Reply to  Rust Buckets

EGR makes a noticeable difference in MPG, which is good for the people who just want to go to the mechanic and get the recommended work done, but for myself I’ll pick a cable-operated throttle and fresh air any day.

Rust Buckets
Rust Buckets
25 days ago
Reply to  Ricardo Mercio

I’ve heard egr makes an mpg difference, but that doesn’t really make sense to me. Diluting the charge air with exhaust is just another way of reducing the amount of oxygen, but closing the throttle a little more does the same thing. I guess you get less pumping losses this way? I don’t know how much pumping losses actually hurt mpg, but you’d have to use a LOT of exhaust down the intake to significantly increase the throttle opening.

Ricardo Mercio
Ricardo Mercio
25 days ago
Reply to  Rust Buckets

Correct, since the engine is just a big pump, pumping loss is a big factor, and EGR lets you get rid of the closed throttle loss. And fortunately there’s a lot of exhaust available to force into the intake.

Widgetsltd
Widgetsltd
25 days ago
Reply to  Ricardo Mercio

Yes indeed. In a similar way, cylinder deactivation systems save fuel by reducing pumping losses. When the MDS cylinder deactivation system debuted on the Chrysler 5.7L Hemi, several Chrysler engineers published a paper through SAE that explained the whole system. If the engine could make the targeted torque value with only 4 cylinders firing, it would typically do so. Preventing airflow through 4 cylinders’ valves/ports reduced pumping losses. Making a given torque output in 4-cyl mode with a higher intake manifold pressure (compared to what would be seen at the same torque output in 8-cyl mode) also reduced pumping losses across the throttle plate.

Cayde-6
Cayde-6
25 days ago
Reply to  Rust Buckets

Really? You coulda answered your own question with 5 seconds of Googling.

It’s not about MPG, it’s about NOx emissions.

Rust Buckets
Rust Buckets
25 days ago
Reply to  Cayde-6

What question? I never asked if it’s for MPG.

LTDScott
LTDScott
25 days ago
Reply to  Rust Buckets

The NOx readings from your tailpipe would likely disagree.

PaysOutAllNight
PaysOutAllNight
25 days ago
Reply to  Rust Buckets

It’s still a problem without PCV and EGR systems, but it’s a much smaller problem with a very much longer service interval.

In addition to the oil and exhaust blend coming from the PCV and EGR systems, there is also some oil that leaks down the valve stems. For most engines, you’d probably be close to a full rebuild before that became a problem on its own, though.

Last edited 25 days ago by PaysOutAllNight
Rust Buckets
Rust Buckets
25 days ago

Considering intake valve buildup is generally not a problem on diesels(a perfect example of a non PCV direct injected engine), I think you’re right, and the valve stem oil is not a big enough problem to be an issue within the lifetime of the engine.

PaysOutAllNight
PaysOutAllNight
25 days ago
Reply to  Rust Buckets

There are at least a few engines that have valve stem leaks. I can’t recall the models right now. But for the vast majority, it’s a non-issue.

notoriousDUG
notoriousDUG
25 days ago
Reply to  Rust Buckets

So we should just let al that clog cats or pump it back into the atmosphere instead?

Rust Buckets
Rust Buckets
25 days ago
Reply to  notoriousDUG

Let all what clog cats or pump it into the atmosphere?
EGR doesn’t exist to reduce the amount of exhaust gases going out the tailpipe or through the catalytic converter, which makes sense considering exhaust is exactly what the cat is meant to handle.

PCV burns the crankcase blowby rather than release it to the atmosphere. I always thought it was kind of interesting to target blowby, because if the piston rings are doing their job, blowby represents less than 1% of the emissions of the car. I would think a catch can to catch the oil on the way to a road draft tube would be perfectly adequate. And guess what? That’s what most diesels and all commercial diesels do anyways, because a diesel doesn’t have a vacuum and therefore cannot run a conventional PCV. Also worth noting that no vacuum=no PCV, and so any car has no functioning PCV at wider throttle openings or if it’s running any boost.

notoriousDUG
notoriousDUG
25 days ago
Reply to  Rust Buckets

It’s cute how poor an understanding you have of both those systems.

Nothing is going to reduce the exhaust gases going out of your engine; that is a fixed amount based on the air going in. The EGR is not changing the amount it is changing the composition of that exhaust. It is reducing the amount of carbon in the exhaust. It reduces the partially burned fuel in it by burning unused fuel, and it reduces the NOx content of your exhaust by lowering combustion temps. Yes, the cat is there to catch a bunch of stuff but the less that goes in the less that comes out; it’s pretty basic. Plus excessive carbon is not good for the system.

Commercial diesels have not used a road draft tube or a catch can for AGES and you can still route crankcase air into the inlet stream without vacuum because the crankcase of ANY engine is pressurized. Modern diesels either run it back into the intake tract or use a complex filter system that captures the oil and drains it back into the engine; it’s a service item because it will eventually oil foul and cause excessive crankcase pressure.
Even the best sealing rings are going to bleed combustion into the crankcase, this is why every engine ever built vents the crankcase somehow. Older diesels often have a system in place to make sure the blow-by from the crankcase can’t cause the engine to not shut down. Ever see the amount of vapor/raw oil an engine running really high cylinder pressure blows out the breathers? And boosted motors? They still recirculate the breather by introducing it into the inlet of the turbo or supercharger where you see atmospheric pressure or lower…

Like hate on the emissions stuff if you want but at least learn more about it to hate it right.

Rust Buckets
Rust Buckets
25 days ago
Reply to  notoriousDUG

I assume by carbon you mean pure carbon soot particulate, and not all carbon-containing compounds?

The point of EGR is to reburn NOx and to dilute the charge oxygen, which reduces combustion temperature, which reduces NOx. It’ll also help reduce hydrocarbon emissions. The EGR is most definitely not meant to reduce carbon emissions, whether you mean soot or co2. Most EGR systems are specifically designed NOT to return soot down the intake because of the obvious intake valve issue.

notoriousDUG
notoriousDUG
25 days ago
Reply to  Rust Buckets

You are not reburning NOx, you are changing the speed and temp of combustion to reduce its formation.
I would like you to tall all the soot I clean out of EGR pressure sense lines and intakes all about how it is not recycling carbon.

Widgetsltd
Widgetsltd
25 days ago
Reply to  Rust Buckets

1. Modern on-road diesels and all marine diesels have a closed crankcase ventilation system. For example, look at the Cummins 6.7L in late model Ram trucks. These use an oil separator/filter on top of the valve cover which ensures that the blow by gases (which are directed into the engine’s air intake) have no oil vapor in them. You wouldn’t want to have an engine runaway!
2. The PCV system on a gasoline engine still functions as a closed system at full throttle or when in boost. When the intake manifold is not under vacuum, the blow by gases vent through the “make-up air” side of the system, directly into the intake airflow. That is, the hose that would normally be the filtered air intake to the PCV system becomes the crankcase vent.

notoriousDUG
notoriousDUG
25 days ago
Reply to  Widgetsltd

Some diesel does vent into atmosphere. Some of the big Cummins do.

Widgetsltd
Widgetsltd
25 days ago
Reply to  notoriousDUG

Well, I did stipulate modern diesels. By that, I mean diesels built recently enough to be equipped with DPF, cooled EGR and maybe DEF/SCR.

notoriousDUG
notoriousDUG
25 days ago
Reply to  Widgetsltd

That is what I am talking about as well
Cummins ISL, ISX and QSX vent to atmosphere.

PL71 Enthusiast
PL71 Enthusiast
25 days ago

Euro-market VW ea113s could be had with an extra fuel injector that would keep the valves clean!

Unfortunately in the US we have to rely on Italian tune-ups.

MATTinMKE
MATTinMKE
25 days ago

I used Seafoam the one time I needed to do this to my GTI. The resultant cloud was something to behold!

MegaVan
MegaVan
25 days ago

Do we have a list of engines that are less affected by this problem?

There have been a couple good articles about the issues surrounding DI (dilution, deposits) – but not much around industry root cause solutions.

Or maybe there are none.

Rust Buckets
Rust Buckets
25 days ago
Reply to  MegaVan

Yeah, port injected engines.

Any direct injected engine that has PCV and EGR will have this problem.

MrLM002
MrLM002
25 days ago
Reply to  Rust Buckets

I would say any direct injection ONLY engines. Toyota/Subaru with the engine in the 86/BRZ uses both port and direct injection so in theory with the proper software it shouldn’t be an issue for those engines.

Slow Joe Crow
Slow Joe Crow
25 days ago
Reply to  MegaVan

It seems to depend on how well designed the PCV system is. The VAG engines seem to generate a lot of carbon where Mazda Skyactiv engines collect very little. I did try Seafoam on my 53,000 mile CX-5 and got some junk but not much.
Engines with a combination of port and direct injection like the Subaru BRZ completely avoid the issue.

LTDScott
LTDScott
25 days ago
Reply to  Slow Joe Crow

Per a racing friend of mine who is a Mazda engineer, Mazda’s solution for this is to have the intake valves run at a higher than normal temperature.

I asked him about this because my afforementioned 2008 Mazdaspeed 3 had very carboned up valves and I was concerned this would be a problem on a newer Mazda 3 too. Based on his reassurance I ended up buying a 2015 with 2.0L.

Taylor Marshall-Green
Taylor Marshall-Green
25 days ago

Mr. Walnut > Mr. Peanut

IRegertNothing, Esq.
IRegertNothing, Esq.
25 days ago

“A super DIY method involves spraying down the valves with brake cleaner, before using a bundle of zip ties in a power drill as a brush to remove sticky deposits.”

Perfection. If there is a way to cobble together a fix with materials already at hand, the noble tightwad will figure it out.

Gilbert Wham
Gilbert Wham
25 days ago

I once attempted to build some field-expedient circlip- removing pliers out of some normal pliers, an old fork and some baling wire. I hurt my hand rather badly, and entirely predictably.

DadBod
DadBod
24 days ago
Reply to  Gilbert Wham

You didn’t put an eye out, so I’d call it a success

Captain Muppet
Captain Muppet
25 days ago

A friend of a friend works on big marine engines. They clean those by dumping walnut shell media into the running engine.

Apparently they have to be in international waters for this as it creates a lot of smoke, and emissions don’t count if you can’t see them from shore.

KC Murphy
KC Murphy
25 days ago
Reply to  Captain Muppet

dumping walnut shell media into the running engine.

I’m trying to envision the new guy’s first day on the job, seeing this on the work order, and being absolute convinced it’s a “left handed screwdriver” snipe hunt.

notoriousDUG
notoriousDUG
25 days ago
Reply to  KC Murphy

True story I once had a John Deere factory tech pour Comet cleanser into a brand new engine while running that was refusing to seat the rings.

He said immediate oil change, two more at a 5-hour intervals and it would either be fine or never make good compression and get replaced.

I know for a fact it ran great for 5 more years before it was no longer in my care and probably still is today.

Bracq P
Bracq P
25 days ago

You will need a lot of air flow to make it happen. Instead of providing one big compressor, it is possible to connect several smaller in Y-Fashion.

LTDScott
LTDScott
25 days ago

BTDT with my former Mazdaspeed 3. That was not a fun job. Took me an entire weekend and I still had to manually pick away at some particularly stubborn deposits. And I still got walnut shell debris everywhere despite using specialized tools to try to keep it contained.

The need to do this job again is part of what made me decide to sell the car recently.

Cheap Bastard
Cheap Bastard
25 days ago

There are better things one can put in brownies.

A. Barth
A. Barth
25 days ago

we have the delicious walnut to thank for two things: delicious brownies

Heretic!!

Mechjaz
Mechjaz
25 days ago
Reply to  A. Barth

+1, Lewin is clearly in the pocket of Big Walnut, going around ruining everyone’s brownies out of spite

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