Hey guys i have been lurking here for a bit, never had anything constructive to add, so i didn't. I have, however, waded through the Evans/sierra/prestone slugfest, and i have no real interest in which is better etc, but i do feel that an important issue popped up in the middle of that thread - and then was dropped. Namely, the electrolysis battery formed by an Aluminum/iron sandwhich submerged in an electrolyte.

In the marine industry (which is where i earn my keep) the issue of dissimilar metal submerged in an electrolyte is taken very seriously, and specific steps are taken to minimize the damage to important parts. The most common protection is to provide a sacraficial anode (made of zinc because it is anodic to everything...i.e. the zinc anode dissapears instead of your propeller, gotta replace those zincs every year, but they are cheap) located near the important metal bits that you don't want to dissapear. Outside the hull that includes sacraficial zincs attached to the propeller shaft, to the struts, to the rudder if it is made of metal, and near any metal seacocks. Of course aluminum outboard motors and out-drives have anodes attached, usually on the cavitation plate. What alot of people dont know is that zincs are provided in the cooling system. Every marine diesel and gas engine out there has zinc "pencils" that thread into tapped holes in the side of the block and protrude into the cooling jacket, to protect the internals of the cooling system from galvanic erosion. These zinc pencils must be replaced every year, or the inside of the engine dissapears.

Are there no such critters in the cooling jackets of rotary engines? THERE SHOULD BE!

From what i understand about rotary engines a common failure mode is O ring failure, and an important criteria for determining the reusabilility of rotor housings is corrosion inside the water jacket near the water seals that compromises the o ring seal groove. An otherwise perfect housing can be rendered scrap by corrosion in this crucial location. So what causes that corrosion inside the water jacket? I have read much about how critical it is to run antifreeze with corrosion inhibitors (and not straight water) in rotary engines to minimize corrosion in this critical area, but what protection has Mazda provided to protect against galvanic corrosion?

Going back to lurk to my corner now...err, it's 2 hrs past go home time, i'm going home.

Mike Parsons

93 VR R1

 

man.. thats interesting as hell.. nice post man.

 

i have been wondering about the same thing lately but i havent really heard of people having problems with galvanic corrosion. if anyone have some good info on why it is or isnt a problem in a rotary please fill us in.

 

Dude, marine engines use seawater for cooling. You would need the zinc pencil if you use saltwater for cooling our engines.


I haven't seen any one posting engine failure b/c of corrosion. Typically, the grooves are fractured due to thermal cycling or the seal itself is damaged.

If you want to be safe, try the zinc pencils and let us know.

 

best newb ever

 

Poman, no one ever posts here about engine failure due to corrosion of the o ring grooves because people here are too busy crackin Apex seals during an overboost/lean condition... go look at an engine that has 200,000 miles on it, not one that only lasts 30 to 40 K. Also, marine engines use a water to water intercooler for engine cooling. Sea water on one side of the intercooler, 50/50 water/antifreeze on the engine side. Yet they still are concerned about galvanic corrosion in the engine. Someone posted that they measured a potential of something like 1.5 volts between ground and the fluid at the filler neck with 50/50 in it and nothing or close to nothing with the Evans...that right there should warrant the cost of the Evans...Also a ground strap from the back of the motor to the front of the motor should help ( i think... i'll have to ponder that a while...would it eliminate the galvanic battery, or intensify it?)

Mike Parsons

 

Go read this:

http://www.mazdatrix.com/faq/rotorhsg.htm

 

Yeah, that was me harping on about the engine being a corrosion cell. I remember a dude once posted a picture of a rotor housing that had practically eaten itself through due to what I can only assume was galvanic corrosion. Now seeing as the inner coolant seal area is so critical for rotary health I would have thought that any course of action that reduces or prevents corrosion damage to this area would be well worth investigating. I genuinely believe this is why so many people are having coolant seal problems, that and the uncontrolled boiling experienced by conventional water/EG coolant systems where the rad cap is losing pressure. That's why evans coolant seems like such a good idea, no water in the damn stuff! Like I said in that other post, the major cathodic reaction in galvanic corrosion is usually the reduction of water and oxygen to hydroxide ions.....so if you remove the water from the equation then the cathodic reaction is greatly inhibited and so is the anodic reaction of metal dissolution (what kills your rotor housings). I'm glad someone else has raised this topic, it could be very important. These Zinc pencils sound very interesting. I wonder if they could be placed in the water drain plug in the centre plate of the engine?

 

Most engines don't last longer than 60K-80K so I don't think it's something to even worry about.

I was the one who posted the voltage differential 0.13-0.15 volt for fresh 50/50 and 0.08 volt for fresh Evans NPG+.

I don't drive my car that often anymore so I think Evans is perfect for this type of use.

 

Good post Mike. And good to see a fellow boater (I assume?) in here.

My Baja has an electronic anti-corrosion system in addition to the sacrificial zinc anodes. This is similar if not in fact the same as Mercruiser's MerCathode system.
(I have a Yamaha Hydradrive I/O with the 454 cid big block). As we know this system creates a protective field that surrounds the outdrive when it is immersed in water. One wonders why at the very least there are not zinc anodes in the block of ALL car engines.
I mean, what could it hurt?

 

Well for one, a service visit once a year to get the zinc changed. And how much would that cost? We are the minority. Most Americans can't even seem to get their oil changed every 3K miles or rotate their tires.

 

The 2 failures mentioned in the link sound like the failures mentioned in your thread by someone who had smoking and coolant in the exhaust on startup. Were those reused housings?

 

I think the solution of zinc pencils is a good one, but where would you put them? I also think the problem is the engine is not designed to last as long as we are forcing it. In Japan, cars are replaced every 3-4 years. Due to lack of supply of 3rd gens. we are trying to make it last 10+ years. I suspect the Mazdatrix identified failure of the "O" ring groove is caused by a combination of galvanic corrosion and heat cycling. Ordinarily, one wouldn't expect such a smallish heat cycle to cause such a robust part to fail, but it may cause small cracks to form which are then enlarged preferentially by galvanic corrosion. This can have two effects. First, the surface becomes rougher, which can abbrade the "O" ring as the parts expand and contract, and second, the groove can enlarge enough to allow too much movement of the "O" ring.

Best solution - Mazda begins production of a new RX-7 so we only work with young cars

 

But if corrosion is a factor in determining if your housing will be reusable come rebuild time, why not pay attention to it?

I've been using Mercedes coolant for a while now. Mercedes has been running aluminum engines for ever and from what I've read it seems that they have an excellent corrosion inhibitor for aluminum. I think that I also read somewhere last year that Mazda was either intending on purchasing their coolant from Mercedes or reformulating their own to include the same components as the Mercedes coolants. A good question would be what kind of coolant is coming in the 8's? I'm sure they don't want new engines dying in 100k miles after a coolant seal kicks it. (my n/a '91 lost it at 102k miles.)

 

I've got the mercedes coolant in my rex for now, but I'm going to swap it for evans as soon as I can find a supplier in the UK. My old man swears by it, he's been using it in his all-aluminium rover V8 for years with no problems whatsoever. I think the problem with the rotary is the unusual combination of iron and aluminium components leading to galvanic corrosion. I'd also be interested to learn how Mazda have tackled the coolant seal problem when developing the RENESIS. Perhaps coolant seal failure isn't such a problem on the N/A rotaries? I suppose only time will tell.

 

Coolant seal failure at 50-60K is not a problem on the 2nd gen turbo. They last beyond 100K. It's a combination of heat cycling, higher thermal output and then the reduction in system pressure by moving from a 1.3 bar to 0.9 cap.

 

From the mazdatrix link:

"Here is the real enemy of rotor housings - corrosion! If the anti-freeze is not changed frequently enough (or left out!), the water starts eating away the aluminum of the housing. This one is junk because the corrosion has gotten into the water seal area."

Know it alls will say 'Corrosion is not a problem' but the fact is antifreeze contains inhibitors to eliminate galvanic corrosion. If you dont change it regularly the inhibitors become depleted. I use the "100,000 mile" stuff and still change it every two years. The zinc anodes seems like a good idea for forgetful folks. They would not be practical for a manufacturer to supply because of cost and the fact that they need to be cleaned periodically.

However, J C Whitney offers one for radiators, which makes me HIGHLY suspicous of their practically

http://www.jcwhitney.com/webapp/wcs/...=-1&PID=952457

 

If you run fresh antifreeze or water and Water Wetter every year I don't think you have a thing to worry about excess corrosion. Even the cheapest brand anti-freeze out there has corrosion inhibitors built in. 13B's probably do deplete the inhibitors much faster with our perfect little aluminum/iron sandwiches - built similar to a battery!

For $12.99 I like the anode good ol' JC has - it sure as heck won't hurt anything and probably WILL add an extra bit of protection. If it gets "eaten" in a year then its doing the job. I just ordered one, remind me to post next year...I just need to figure out where/how to install it in our cooling system since it needs to be submerged constantly to be effective.

Anyone have any ideas where to put it? And don't even THINK of telling me to shove it up my ***

Best Newb thread in a while - good thinking!

 

It needs to be connected electrically to your engine (grounded). So, if you install it in your radiator, be sure your radiator is grounded and not just on the rubber bushings. In the engine filler neck would be a good location.

 

Filler neck would be ideal except it needs to be immersed...hmmm

 

If you look at the picture at JCW it is made to ground on a full size filler neck and hang down into the coolant. Kinda like a tampon

 

Placing the anode in the radiator would protect the radiator, which doesnt really need protecting, especially the all aluminum replacement radiators that every one on this board seems to use. No dissimilar metal = no electrolysis problem. The anode would have to be in the engine water jacket in order to protect the engine internals.

Mike Parsons

 

You give me too much credit tmiked. I don't know anything, I don't. I've found that it's the best attitude in my line of work. Really...

As I was saying, corrosion is not a problem if you maintain your car. I'm not saying corrosion isn't a problem if you let your car go to hell. Of course it would be a problem even if you're driving a honda.

I changed coolant yearly, new thermostat every year, hoses every year, tested radiator cap every 3-4 mos., preflight check of coolant before every drive. Hell, I even checked the voltage of the coolant. Yet at the end of 50K, I had a blown coolant seal for each engine. And always the front rotor. I don't think galvanic corrosion would do that.

Anyway, if you're running that Dexcool stuff made by Havoline for GM, I would at least google the term. Chrysler stopped using it. Only GM, which specifically designed its engine for this coolant uses it. It's some type of acid. Check for powdery white stuff on your filler cap and radiator cap. Never knew what that stuff was though.

 

No, That is the point of grounding the radiator. If the anode is ELECTRICALLY connected to the engine it will help protect it. It does not matter where it is actually located as long as it is in the same electrolyte solution.
You could wire the anode to the battery through a 4.7KOhm resistor and have an active cathodic protection system. It would drain you battery only if left unattended for a few months.

 

Hmm... How come the OEM radiator is not grounded but in fact are on rubber suspensions? Yet why is the catback exhaust grounded back in the rear of the engine when it's electrically connected to the block?