I pulled my engine apart a few days ago. I had a combustion o-ring failure, and planned to find a warped housing, or bad o-rings, or something. I found a warped housing, but that wasn't what bothers me. What bothers me, is that my new rotor housings, that had less than 15k miles on them are totally corroded around the exhaust ports in the water jacket. I used regular NW Florida tap water, and prestone green coolant in a 70/30 mix. I was running the stock twins nonsequentially. What I gather from this, is that the twins kept so much heat in the exhaust sleeves that some local boiling took place. When the water boiled off, the minerals in the tap water deposited onto the aluminum in the water jacket. After time, I suppose they ate away the aluminum in that area.

Forgive the pictures, I took them with my phone.

 

The moral of this story is to not let a drop of undistilled water touch the inside of your engines.

 

Wow. That much in 15,000 miles?

 

I've started buying the pre-mixed 50/50 coolant and water. Just makes filling the car so much easier, and you're filling it with good water.

I'd rather run a higher antifreeze mix than a more agressive mix due to corrosion. If the car is running hot, find another way to cool it. Corrosion is a bad mamma jamma.

Dale

 

I always thought the distilled water thing was a bit of a wive's tale, but I am a true convert now.

 

wow, you guys never believed that before? why do dthink we mechanics tell you guys this stuff? Causse we like to hear ourselves talk? My voice isn't that nice.! J/K

Glad you understand now why it is said to use it. The minerals and deposits in the tap water are the worst thing for the system. I would reccomend flushing your radiator very well. As if there was that much in the housings, you can be sure your rad is corroded as well.

This is kinda funny as my Dad just had his Tribute overflow hose pop off. he lost coolant and filled it back up with hose water. He said he had heard that before but thought it was just a sales pitch!!haha!!

 

I knew it was better to use distilled water, but I only expected BUILDUP of minerals, not BREAKDOWN of aluminum.

 

I knew it was true, but had no clue it was THAT bad.. Sorry about the luck man.

 

My thoughts exactly. I find it hard to believe that much corrosion could take place in only 15,000 miles, unless those miles were over the span of say, at least a year. The leaching of metals by corrosion takes time. Of course, this isn't to say that using tap water is OK, only that changing your coolant at regularly scheduled intervals is a must.

 

oh damn~ I used it before but when I had a small leak I had to put in tap water, but now I should change it back to distilled mixture

 

Yeah, the car has had some time to marinate. It's been about 15k miles, and about a year.

 

Remember, also, that unless you have absolutely everything apart, you can't flush everything completely out, even the water you are flushing with. Therefore, it's almost a necessity to use distilled water for the last few flushes, to make sure no tap or other contaminated water remains in the system before you refill it.

 

I wonder if cavitation is possible in those passages. It's not related to the water type, but capable of very aggressive erosion.

Dave

 

Use of tap water with coolant will reduce its effectiveness and may cause more deposits, but it is not necessarily more corrosive than distilled water**. In some cases, deposits, depending on the specific mineral content of the water, will actually reduce corrosive effects, but may also cause liming and could affect heat transfer somewhat. The primary cause of corrosion in our engines is going to be electrolysis as result of dissimilar metals in contact or close proximity. Coolant in sufficient concentration is designed to reduce this activity.

Also, is there any evidence of an exhaust leak into the water jacket? Combustion leaks could result in a lower ph (acidic) solution. This can be tested for. Additionally, the higher temps in the area of the port will also result in an accelerated reaction (of any kind).

** One caveat on tap water: I would definitely avoid using SOFT water out of household water softeners or other ion-exchange type systems. There is always some residual salt (sodium chloride) in these systems which will increase galvanic activity and will attack aluminum.

 

That sounds a whole lot like a battery. Ever do the trick with the nickels and dimes making a battery as a kid? Nice to know that our engines can have a use even when they're blown.

 

Yea, I cant say the same for the previous owner but I have run only distilled water and the green AF. I was low on coolant due to a small leak and I limped it over to a Wal-Mart about 2miles away just so I could get some AF since everything around me that was available only have tap.

~Kris

 

Which is why I carry a nalgene quart bottle of distilled water.

(It doubles as a useless fire extinguisher )

Dave

 

One thing you could do is put some some vinegar and run the engine to neutralize. After that flush with distill water and put 50/50 using deionized water..

Or just use Deionized water and coolant and change it after month or two..

 

like speed o light said the electrolysis is the killer. i posted a question a few months ago asking anyone to check the voltage in their coolant. put the test lead on the neg terminal and the other in the coolant neck without touching any metal. see what the reading is. turn on ac lights etc and see what it is. due to a ton of delco heater core failures they have started to send out a local rep to check the voltages before they will warranty a new unit. would love to get some numbers. obviously done when the engine is cool and running. using distilled is something that i have always thought was a good idea and seemed to make sense to do it if possible but have never seen any controlled tests where it mattered. and since gm is getting sued off their *** for the leaking manifold gaskets on their trucks you would think if they thought it would help they would instuct dealers to do so. that said i used distilled in my fd.

 

same local corrosion near exh ports, per pic, at 3 other similar housing face locations? any other places?

 

yikes.

 

have you ever used tap in your steam iron ??? who didn't teach you right ! WOW.

 

I don't know how true this is, but I thought I read that "distilled" water doesn't help, and may even hurt, and that "deionized" water was the stuff to use.

I know that I have some concept of "special water" in my head, but I have a hard time remembering which is best for cooling systems -- dionized (I think this is right), distilled, demineralized. I suspect I am not alone in this confusion since this thread has already bounced among the three without anyone pointing out the distinction. Does anyone know? What is the right answer? Which type of "special water" is the best one for our rotaries?

-Max

 

There is a bit of corrosion all through the rotor housings, but it's nowhere near as bad as around the exhaust port area. The irons are fine.

 

Distilled water, Prestone (GREEN) and one can of waterpump lubricant/rust inhibitor.

You should see engines I take apart after 100,000...NO corrosion. You also get 100,000 plus miles out of your water pumps.