What causes Carbon Build-up and How to Avoid it?

Andras · 06-02-2004, 10:16 AM

Having just torn down the motor (or is it engine? we non-American-born have such trobule with such distinctions!), I notice quite a bit (more than I'd like) of carbon build-up on the piston tops, the valve tops, and even the underside of the valves. In a perfect world, shouldn't there be nice brown deposits on these surfaces, not black?

Would the following preventative measures help avoid such build-up:
1. Keep revs higher than 4,000.
2. Use higher octane gas.
3. Use Techron every 3,000 miles (just before Oil Change).
4. Indulge in an occassional "Italian tune-up".
5. Other?

stlrj · 06-02-2004, 10:29 AM

How about #1. Having your mixture checked and set to factory spec?

yelcab1 · 06-02-2004, 10:35 AM

In a water cooled engine, having a leaky head gasket will solve that real quick.

Superman · 06-02-2004, 11:14 AM

It does not bother me that you seek input, but for the record I told you it's normal. Further, Quartz Grey Metallic owners would never try to fool each other.

As another data point, when I tore my engine down, it had been running perfectly, with perfect air/fuel mixture and good ignition. Also, I use only Chevron gas, considered to be the best on the market for avoiding unnecessary deposits.

Water, or even just moisture in the air will remove it. My pistons sat in my (humid) garage for a few weeks, and the stuff just FELL off on its own. So, I suppose you could mist them sometime during shutdown, but the carbon falling off might help score or wear your cylinder walls.

Again, I say this is normal, but I'm also interested in the findings of others. Is there anyone out there who has disassembled an older engine and discovered something other than black and grey carbon deposits?

yelcab1 · 06-02-2004, 11:17 AM

I got black stuff all over the bottom of the valves, the crown part of the heads, the top of some pistons, and the bottom part of the valves below the valve guides. Fact of life, I say.

Flying Toaster · Flying Toaster's Garage

I just had my heat exchangers off & the exhaust ports were a 3rd of the size they are supposed to be from carbon buildup....

Rot 911 · 06-02-2004, 12:12 PM

Quote:

Originally posted by Flying Toaster
I just had my heat exchangers off & the exhaust ports were a 3rd of the size they are supposed to be from carbon buildup....

I find this hard to believe. Are you sure it wasn't from bad valve guides leaking oil into the exhaust?

Rot 911 · 06-02-2004, 12:14 PM

Here is one of my pistons from my 3.2 with 133,000 miles. The rest looked about the same.

dd74 · 06-02-2004, 12:20 PM

Use only premium gas. "Techron" about every other month - the gas is that bad, even premium.

RickM · RickM's Garage

Let's throw initial break-in into the mix.... http://www.mototuneusa.com/break_in_secrets.htm

Half way down the page....Honda F3 pistons.

kqw · 06-02-2004, 12:47 PM

About once every two years, I have an engine vac. done.

Paulporsche · 06-02-2004, 12:59 PM

I second stlrj.

If you are running too rich you will get a lot of buildup.

Also, I am not sure premium will help you if the engine does not require it. Maybe some others can chime in, but I don't think it is true anymore that premium has more or better detergents than lower octanes.

I think your other suggestions are better. Rev it up, do the Italian Tuneup and use Techron. There are other proprietary engine cleaning systems available out there that run chemicals through the engine for cleaning, but I have never used them.

Paul

Bruce Huling · 06-02-2004, 01:05 PM

check out the string awhile back on this website regarding spraying a little water into your intake at rpm to remove carbon deposits (old trick). then sit back and watch the fireworks as the experts weigh in.in.in.in.in.in.in.in.
bh

beepbeep · 06-02-2004, 02:08 PM

Yeah, rev it to 5000 RPM and pour soe water in it...it will blow out your carbon in no time. Make sure to start gently if you suspect lot's of carbon, or you might get big lumps of it lodged on valve seats.
It can suck lot's of water at those revs, just don't get it hydro-locked.

But it works very well...i did it two weeks ago on my daily driver that has been pinging despite low C/R and lot's of fuel. I just had to make sure it wasn't the carbon build-up and it was.

Andras · 06-03-2004, 03:51 AM

Thanks Guys,

I've heard of this "method", as the Miata guys and the motorcycle guys also recommend it.

One thing with the CIS, though - where in the CIS tract do I introduce the water, and through what means - syringe, sprayer, high-pressure hose (just kidding!), and in what measurable quantities. Never having seen it done, I don't have a "feel" for how much is enough, how much is too much.

In motorcycles, there's not much "stuff" between the velocity stacks and the intake valves. But in a CIS, there's a lot of plumbing between here and there.

beepbeep · 06-03-2004, 04:17 AM

Best bet would be to use one of those bicycle plastic water-bottles with a hose. You should introduce it after CIS barn-door, detaching auxillary air valve and connecting water-hose to it (w/o introducing leaks) would be easiest. Or if there is some sort of small rubber hose connected to plenum that can be detached and used for this (there are lot's of those on 930's).

You can push fair amounts of water trough the engine at those revs...rev it and do a good squeeze on the bottle. You'll notice that you push too much water when engine starts cutting out.

Third way: run your car on E85 fuel :-) It will clean everything from it...optimal A/F ratio is around 8.7:1 though...but it has much higher octane rating than ordinary gasoline. I'm running my beater on pure E85 now as gasoline prices are trough the roof.

Flying Toaster · Flying Toaster's Garage

On my MFI car, do I just remove the air cleaner & hit each stack individually? Will the car run with the air cleaner housing removed? -John

88911coupe · 06-03-2004, 08:28 AM

What is the best method to introduce the H2O in a 3.2 Motronic engine?
TIA

tsuter · 06-03-2004, 08:44 AM

Try here: Water CIS???

De-carboning with water, reloaded

Evans, Marv · 06-03-2004, 10:17 AM

In the late fifties, we used to get rid of carbon my pouring water down the carburator. It would work OK by pouring it down an intake stack at a time. We used to pour it in with a bottle until the motor almost stalled & would stop in time for it to recover. Be careful doing it in your garage or some other sensitive place, because a HUGE, GRAY BLACK cloud of smoke comes out of the exhaust. Nowadays there will be somebody around to say something negative about that.