Tuesday, December 5, 2006

VW - The Coca-Cola Myth

> I still keep getting guys telling me how clean n shiny my rusty bolts would > end if I put them for a night on coke


Bright & shiny? Myth.

But rust-free? True. ( Okay, sorta true.)

Coca-cola (and most other soft drinks) contains phosphoric acid. After eating the enamel off your teeth it gives you the extra zing American's expect in their soft drinks. Coca-cola also contains carbonic acid, created whenever carbon dioxide is dissolved in water. Both are effective de-rusting agents. But not very fast. While Coca-cola is acidic, and while the acids it contains are specific 'getters' of oxides, they are quite dilute; as rust removers they don't work very fast. Raising the temperature and leaving the part in the solution for several days is usually required If you want to remove the rust. But if you simply want to break the bond on a rusted nut & bolt, an overnight soak should do it.

The real question is why someone would use Coca-cola when they are literally surrounded by more effective -- and less expensive -- rust-removing agents. You can buy various acids, including phosphoric, from Home Depot... and probably already have a few around your house. (Tile cleaners often use hydrochloric acid and every old car battery contains some sulphuric acid.) And if all you want to do is loosen a rusty fastener then you should be using Kroil or Mouse Milk. (Yes, 'Mouse Milk.' It's a brand name. See any good machinist-supply catalog.)

Got rusty bolts? The least expensive method of restoring them is simple reverse electrolysis. That is, a conductive solution (salty water will work) plus a battery charger. Look it up. Several sites on the internet devoted to cleaning metal.

(It might also be a good idea to read what's in the stuff you eat & drink. The world is full of surprises :-)

Ed. Note: The above got several people to try electrolytic rust removal for the first time, with results that ranged from delightful to mushroom clouds and prompted the following:


Electrolysis -- You gotta clean the thing first.

Yeah, I know... it's a mess. But the odds are it's an oily, greasy mess. And there may still be some paint under all that rust. Electrolysis does not work on grease. Nor paint. You'll end up removing the rust from all around the greasy or painted part... which may be what you want but usually isn't. So degrease it.

A hot solution of lye (ie, the traditional 'hot tank') is the time-proven method. Of course, if you get some on you, you tend to jump around and make funny noises. TSP -- trisodiumphosphate -- is a more benign getter of grease and does a pretty good job on paint. Just keep boiling the dirty part until it's down to Basic Rust then pop it into your electrolytic bath. (Be sure to use real tri-sodium phosphate. There is a common household cleaner with the BRAND NAME of 'TSP' that does not contain any phosphates at all. Paint department usually carries the good stuff [you use it to scrub old paint before laying on new]. )

Same holds true for your iron electrodes. If you clean them before wiring them up, they will have more effective surface area.

Handiest clamps I've found were pieces of copper pipe. Cut off a piece about an inch long, wrap your wire around it and solder, then drill the thing to accept at least three sheet-metal screws. Slide over the re-bar, tighten the screws, connect the wire and away you go. The re-bar gets eaten up but the clamps will last just about forever.

If you've used a concentrated salt solution for your electrolyte then you'll need to BOIL the part in clean water once the rust has been removed. The derusted, boiled part will develop a haze of rust as soon as you lift it from the boiling water so be ready to deal with it. Either give it a shot of primer as soon as it's dry or hose it down with WD-40. (I don't recommend the use of lye as a electrolyte. Any salt (as opposed to acid) will work. I use washing soda.)

A big advantage to electrolytic rust removal is that it only takes away the rust, not the metal attached to it. With sand blasting, everything goes -- and leaves a surface that's rough as a cob.

Save the Coca-cola for rotting out your teeth the way God and the American Dental Association intended. If you got rust, there are smarter, less expensive ways to get rid of it.

-Bob Hoover

1 comment:

jon strom said...

Subject: cool tins vs. deflector plates

Hi Bob,

I have been reading and re-reading your blog entries as I prep my engine for assembly. I have learned a wealth of knowledge from your experience and logical explanations. One thing you seem to have not discussed is the difference between Type one air deflectors that mount under the cylinders and the Type 3 "cool tins" that are all the rage at the kiddie parts stores. You mention cool tins briefly in your entry about trikes, but I have found a can of worms on websites such as Samba, etc. when researching the difference between these two methods of cooling the cylinders effectively. My Type 1 upright engine is bound for a fiberglass kit car, that does not have a method of sealing the bottom half of the engine compartment from the top half as in a stock VW. I am ducting fresh air to the fan intake from a remote location, but I still am unsure of which method is better at cooling the (bottom side of the) cylinders.

The argument seems to be VW designed the cool tins to be used with the "pancake" engine cooling setup, and are ineffective when using an upright fan housing, and then there are those who swear by them. I am just trying to discover which is actually better at keeping my cylinders cool. Using the "cool tin" style would make it a lot easier to create a vacuum/venturi effect to help exhaust the hot air out the rear of the vehicle and prevent it from recirculating back to the fan intake. But I don't want to use them if they are ineffective at keeping my cylinders cool.

Any insight of yours would be appreciated.


Jon Strom CBTE
KDSM Fox 17