RX-7Impreza

ok i have these seals from this place click here they are the Buna N seals

here are the properties of the Buna N seals click here

i want to use them on this rebuild and they are a lot cheaper than oem but high quality.

i just want to know if this is at all taking a risk

they are only good up to 250 *F

Justin

niner

I'd say go w/ OEM
The savings in price would be negligable compared to the chance of them failing.

jspecracer7

You'd probably be taking a risk using them.

...However, you could buy them anyways, and be the Guinea Pig for all of us

FPrep2ndGenRX7

The viton seals look like a better choice. www.hayes rotary sells some teflon type seals that are almost reusable if removed carefully. Otherwise I would use factory seals so you won't question it later.

Poindexter10thae

iTrader: (2)

If these seals are only good up to 250 F then you should know better! Forget about using them, we all know what kind of extreme heat a rotary produces. The rotor housings get hotter than 250F when you are at normal operating temp(remember, your temp gauge is how hot your coolant is, not the combustion or the housings)

mazdaspeed7

The housings do not get 250 degrees. The combustion is much hotter, but only a small porting of that heat makes it into the housings. The housings arent any hotter than the water is. Look at it this way. If the housing gets more than ~210-220 ddegrees(boiling point of water/coolant in a pressurized system), you will have flash boiling of the water on the surface. Anyone who knows cars knows this is very very bad. Our cars have such over-engineered cooling systems compared to pistons FOR this reason. It was designed to have enough cooling ability that the coolant will not flash boil.

BTW, if you get yout rotor housings 250 degrees, the engine is toast from being overheated anyways.

If you look at the properties, these ARE recommended for automotive coolant seals.

peejay

Yes the housings will exceed 250 degrees! BigWoogie (nice name btw ) is right - the temp gauge only registers coolant temperature. Heat always flows form hotter to cooler - the metal has to be hotter than the coolant for heat to get transferred to the coolant.

The stock seals are good to about 1600? degrees F. No they don't normally see direct combustion heat, but they CAN... if the engine is cold and the metal hasn't expanded yet, the housings will be "loose" in the tension bolts. (#1 reason why you need to baby your car until it's fully warmed up)

mazdaspeed7

If the housings get over 250 degrees, why does it not flash boil the coolant?

peejay

Because the coolant is under pressure from the water pump. In-block coolant pressure is around 30-40psi.

That's why you have to install a restrictor if you eliminate the thermostat... without the restrictor, the water just flows right through without having any water pressure and it DOES flash-boil.

mazdaspeed7

I still disagree. Even if the pressure inside the block is 40 PSI, thats still not enough to raise the boiling point of the water high enough to allow the housings to be more than 250 degrees before it flash boils.

Would anyone like to find some physical evidence that I am not right here?

Look here at neoprene. It is RECOMMENDED for aotomotive coolin systems. But what is its max temperature? 225 degrees. Why would it be recommended, if the engine block got hotter than that?

mazdaspeed7

BTW, I have seen rotaries run without a thermostat, and they werent flash boiling the water. Im sure its possible, but its not very likely at all. The rotor housings just dont get hot enough to do that.

I dont remember the guys name, but there was someone here who raced(in ITS I believe) who NEVER ran a thermostat. If he wasnt having problems flashboiling the coolant under those circumstances, they what makes you think a car on the street which spends most of its life at low loads/low rpm's will have a problem with flash boiling?

Felix Wankel

Well when is your water temp higher? Sitting in traffic or blasting down a straightaway?

Cheers!

Boiling point of water at 40 psi is 267.3°F


Reference:
Moran, Michael J. & Shapiro, Howard N., "Fundamentals of Engineering Thermodynamics" (New York: John Wiley & Sons, Inc. 200), page 856 Properties of Super Heated Water Vapor (English Units)

mazdaspeed7

You still ahvent convinced me that the pressure inside the housings is 40 PSI. I think its 13-17 PSI (same as the pressure cap) throughout the system.

scathcart

I'm with Mazdaspeed on this one. If you put an aftermarket temperature gauge in with the sending unit in the stock location (tapped during a rebuild), the sending unit sees the tempertures of the "40psi coolant" around the block. Go check out your guages, I checked mine. It sure doesn't read 240 degrees, in any situation for me, be it track, city, or whatever.
The pressure does indeed raise the boiling point, but it doesn't mean the temperatue gets that high.
I also doubt that the pressure reaches a level of 40 psi.
Sean Cathcart

peejay

The coolant will be cooler than the metal, since the metal is constantly rejecting heat to the coolant. How can the metal transfer heat to the coolant if the metal isn't hotter?

Ever notice how on really hot days, when you shut the engine off after a hard run you hear boiling sounds under the hood? That's the coolant boiling inside the engine. When the engine is running, there is water pressure in the block, increasing the boiling temp. When you shut the engine off, the water pump stops pressurizing the engine, and block pressure equalizes to a balance between block pressure and radiator pressure. This lowering of pressure inside the engine causes the boiling point to drop, and the coolant to start boiling. Part of it is also because the coolant is no longer flowing through the engine, it remains stationary and the remaining heat difference between the metal of the engine, and the coolant, gets equalized, raising the temperature of the coolant.

Try this experiment. Run your engine and note the coolant temperature on a mechanical gauge. Shut the engine off and watch the gauge slowly go up a little bit for a few minutes.

mazdaspeed7

The water is very close in temperature to the engine block. Mazda spent a lot of time designing a cooling system that was efficient enough(and big enough) to keep the engine well withing acceptable limits

Did you ever notice that engines regularly run right above the temperature at which the thermostat opens at? As soon as the thermostat starts to open, the cooling capacity of the engine high enough that it wont climb any higher except under abnormal conditions, which cause the car to overheat. We're talking about normal operation here. I do think that if you overheat the engine, the seals will go to or above 250 degrees. but then you need to rebuild anyways, so whats the big deal?

The water doesnt get any hotter after you shut the car off. It just loses the pressure. Remember, water under atmospheric pressure boils at 202 degrees. That is WELL within the safe limits of those 0-rings. The pressure is what raises the boiling point to ~220 degrees. Even then, the o-rings are still good.

RX-7Impreza

212 degrees at sea level actually...

oh and i dont know about your engine but mine sure as hell doesnt boil coolant after i turn it off. i have seen a car with boiling coolant and it will spit steam from every place it can. my friend boiled his coolant and it ran out of his heater core onto his computer and screwed everything. and your coolant doesnt build up to 40 psi at any point in your cooling system or your cap would blow off.

i have a potatoe gun that fires potatoes 300yards at roughly 25 -30 psi max. there isnt that much pressure in your coolant system. if there was you wouldnt be able to take your cap off after the car was running.

Justin