could detonation blow a water seal?

[Martiny]

Originally posted by MillSpeed
Hells No! Well, not unless the rotor housings/end plates are warped. The water seals are just like giant rubber o-rings which rest in grooves machined into the rotor housings (or the end plates in early engines). If they are exposed to combustion gasses (which are at extremely high pressures) they\'ll burn through in no time.

All right.

So, when the seal fails, what is it that causes the water to pump out the expansion tank, then?

and

If your combustion chamber is as tightly sealed as you suggest, then what do we need an O-ring for?

[Oedipus Rex]

surely if the are at the tops and bottoms they are only on the intake/exhaust part of the cycle, rather than the combustion section.

[Martiny]

Originally posted by Oedipus Rex
surely if the are at the tops and bottoms they are only on the intake/exhaust part of the cycle, rather than the combustion section.

Nope, they go right around the housing.

[MillSpeed]

Usually, water gets chucked out of the expansion tank when the little return valve on the AST cap gets stuck shut. When the engine cools and the coolant contracts, the engine cannot draw coolant back out of the expansion tank. If you keep adding coolant to the engine, eventually the expansion tank will overflow. Alternatively, the AST cap spring might have become weakened with age, letting coolant flow to the expansion tank before it\'s built up any sort of pressure in the cooling system.
When you get warpage/water seal failure, it\'s very similar to head gasket failure on a piston engine. The increasing coolant system presure overwhelms the AST cap and some coolant gets forced into the expansion tank.
The O-rings are there (I assume) to keep the coolant from seeping into the rotor housings. You\'d be surprised the sort of gaps water can get through via capilarity!

[Glenn Butcher]

Martin could well be right I think. But there would possibly be a mixture of oil/fuel etc. in the coolant if this happens.

Combustion is not only sealed by the Apex seals, it is sealed by Apex Seals, Corner Seals, Side Seals (all aided by the springs), rotor face, rotor housing face, end/centre plates (and the way it is all bolted together).

Generally the weak points are the Apex seals, Corner seals, (sometimes side seals), and the side housings.  This is where good apex seals and dowelling in an engine all helps.  Even if you do all of this, it doesn\'t mean you can get away with much detonation!!!  but it may be a little more tolerant.

Be interested to see if Carl, Tim have further comments on the weak points from the combustion point of view in the engine.

I think have the pressure checked - should hopefully provide a few more clues.

Oedipus Rex - I was actually going to ask how many miles were on it, but you said it had been rebuilt recently, so it shouldn\'t be corrosion.

[Glenn Butcher]

Also - with extreme detonation the plates/housings can literally seperate themselves. Hence the mixture of oil/water in either and/or the cooling system (both oil and water), and coolant in the combustion chamber --> leading to loss of coolant.

This is why I think Martin\'s point is quite valid.

[scooby_si]

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Si

[antnicuk]

Hells No! Well, not unless the rotor housings/end plates are warped. The water seals are just like giant rubber o-rings which rest in grooves machined into the rotor housings (or the end plates in early engines). If they are exposed to combustion gasses (which are at extremely high pressures) they\'ll burn through in no time.

slightly confused i think!   very early models had the O ring grooves in the rotor housing,  for the last 20 years or so the grooves have been in the end and centre plates except for the Renesis RX8 which are back in the rotor housing!   I wish they would make up their mind  :confused:

Like any gasget,  if it was exposed to the full pressure of combustion it wouldnt last long but because the o rings are in grooves the are protected and only have to seal the tiny gaps that two metal surfaces mating leave, but still take a bit of flack which is why you can pressure the water system if its knackered.  The combustion o ring is teflon coated and is quite tuff, (try scraping an old one out of its groove!

Of course i may be wrong:(

[petemillis]

Why not just pull a spark plug to check for signs of water contamination? If none, then that\'s not your problem.

[Glenn Butcher]

May be hard to tell from the Spark Plug, it would be more obvious from lots of WHITE exhaust smoke, or coolant in the oil, or oil in the coolant.

It could still be something silly in the coolant sytem!  I\'m sure we\'ll find out soon.

[Oedipus Rex]

bloody FD\'s and there coolant system, a royal pain in the arse.

Got a new AST cap today but I reckon I\'ve sussed it anyhow. After going out for a proper spin tonight I parked her up and still had the light on. Noticed a load (well some) of steam coming up under the passenger headlight. Gonna jack her up tomorrow and see if a hose has come loose from the rad somewhere.

[MillSpeed]

Originally posted by antnicuk
slightly confused i think!  

Ah, my mistake. The water seals moved to the side plates on the post \'86 13B\'s. I wonder if there was any particular reason for Mazda moving them back in the Renesis?

[iaint]

Originally posted by MillSpeed
Ah, my mistake. The water seals moved to the side plates on the post \'86 13B\'s. I wonder if there was any particular reason for Mazda moving them back in the Renesis?

My money would be on an engineering compromise.  

Probably sealing in the side plates have some drawbacks (like metal thinness amybe) but sealing in the other position places them in a hotter position (just a guess that the turbo\'d engines run hotter...).

[MillSpeed]

Thinking about it though, if the detonation had been severe enough to separate the rotor housing from the side plate, then wouldn\'t the symptoms would be alot more pronounced than an overflowing expansion tank? I mean surely apex/corner/side seals would\'ve been severely damaged (or even spat out!) leading to, at the very least, the car running like ass.

[Glenn Butcher]

Yep....

Also - with extreme detonation the plates/housings can literally seperate themselves. Hence the mixture of oil/water in either and/or the cooling system (both oil and water), and coolant in the combustion chamber --> leading to loss of coolant