There are two major types of automotive coolants out on the market today.  The first type is ethylene glycol, and the second type is propylene glycol which is less toxic than ethylene glycol.  Animal pets have been known to ingest coolant left sitting around due to it's slightly sweet taste.  An example of propylene glycol is Sierra™ brand coolant.

There are a number of coolants that tout "high mileage" use.  This type of coolant has not be tested adequately with rotary engines.  We do not recommend using this type of coolant for such long durations (up to 100,000 miles) between flushes.

The rotary engine relies heavily on it's cooling systems.  We recommend flushing your coolant at least once a year.  We recommend Prestone™ coolant for your rotary engine.

Click here for cooling system flush procedure!

This is a post from the RX-7 Internet Mailing List from KD Rotary on Dexcool...

From: KD Rotary 
Sent: Thursday, March 30, 2000 11:57 PM
Subject: Re: Coolant question.

> Hey are the three following reasons and
> opinions for what they are worth...
> the first time we had rebuilt an 87 tll...the customer
> installed at home with our help and we watched him fill it 
> with dexcool (havoline) and distilled water...six months 
> later at the drags on a stock engine he spiked
> at 18 lbs and blew we tore down for him and the
> engine coolant ports were completely corroded...and the
> coolant seals showed really excessive
> corrosion...we were very suprised..he flushed the heater
> and rad...went back to prestone..
> the second was a hayes rebuilt that came to us with 8 K on 
> it..the 3mm were done poorly and the engine failed..when
> we tore it down it was the same...the hayes coolant seals
> were pitted terrible and the white powder all
> over the aluminum rotor housings...we asked the cust and
> he said he used dexcool and distilled water...the third
> was 93 that the customer changed to dexcool at 55K
> miles...the engine had coolant seal failure at
> was the same as the other three as the coolant seals were
> destroyed...the engine in this one was never beat..older
> gentleman who maintained it religously and
> never over heated...all highway now
> what...while we believe dexcool is a great product we
> believe they may be several reasons for this issue that is 
> not prevelant in piston engines...(I ran dexcool in my
> 626 with never an issue...191K)...
> my opinions are this...
> 1. maybe the dexcool is very sensitive to the old
> antifreeze in system...maybe some chemical reaction if not 
> flushed completely???
> 2. the rotary by nature pushes some hydrocarbons into the
> coolant system on cold starts...cannot help it...they all
> do it..thats one reason for the ast
> tank and why everyones overflow bottle gets that ugly
> black stuff on the dipstick eventually...regardless maybe
> the dexcool mixed with hydocarbons
> causing a caustic reaction???
> 3. the one main thing I have noticed is that they are all
> turbo
> the coolant takes much more extreme abuse from heat and 
> turbos???maybe with all three issues combined it causes 
> what we have seen...
> hope this helps...holler if any issues or 
> questions...thanks a
> mill..dave@KDR
> KD Rotary Import Performance
> 862 Fenwick Street
> Allentown PA 18103
> Ph: 610.433.2033
> Fax: 610.433.2405

Another post taken from the FC3S Internet mailing list from Prestone customer relations...

Some European automobile manufacturers request that a phosphate-free
antifreeze be used in their vehicles. This issue is related to the
extremely high mineral content of the water in Europe. If you were 
to mix an antifreeze that contained phosphates with the type of water 
they have in Europe, it may produce deposits that can settle in the 
cooling system and promote corrosion. However, in North America we do 
not have this type of water problem. Typical North American coolants 
have contained phosphates (which is part of the corrosion inhibitor 
package) for many years.  Therefore, the question of phosphates is a 
non-issue here in North America.  Prestone antifreeze/coolant is 
completely safe for use in both foreign and domestic vehicles. For 
those consumers who would feel more comfortable using a phosphate-free 
antifreeze, our Prestone. Extended Life 5/150 is phosphate, silicate, 
and borate free. This coolant uses a special chemistry and technology 
that extends the life of the corrosion inhibitor package so that it 
lasts for five years or 150,000 miles (whichever comes first), and
is safe for all cars and light trucks (old or new).

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