My engine has atleast one cracked apex seal. I say atleast one because I bought it with one and then let previous owner drive and he managed to overheat it again. I don't even know if it is possible to crack two and the engine to still be running. But rotary engines can take a beating if you talk to them nicely. . Anyways; my idle has been erratic for awhile and I just assumed it had something to do with the cracked apex seals. Though since I've ran out of "projects" to do with the fc I figured I'd ask because if not I can start looking for vaccum leaks etc.

 

Why wouldn't you look for vacuum leaks? Thats the first thing i would check if i had a weird idle. Whens the last time you did a tune up? Plugs, wires, air filter, etc. Try cleaning the MAF? How do you know you have a "cracked" apex seal?

 

do a compression test, there is lots of other things that can cause erratic idle, like a, intake vacuum leak.
my rx7 has had low compression on the rear rotor since I've owned it and it idles/drives fine.

 

How many times has it been over heated? You need to avoid that from now on... If you somehow know that the engine has a cracked apex seal then I wouldn't drive it. You could score the housings and end up having to buy and new engine.

 

IF the idle is realatively low, in the 400-800 range, then idle the engine and spray STARTER FLUID around the vacuum hoses and the mating surfaces of the intake manifold plus toward and around the fuel injectors bases. If a leak is there, then the idle speed will increase noticably.

Or it could be a matter of a vacuum line going to a place it should not be going. Line a fuel injector air bleed nipple connected to a source of vacuum. Not good. CAuses bad idles. Or a air line off one of the oil injectors causing a unauthorized air leak.

 

Oh thanks for the input guys; I couldn't find any vacuum leaks anywhere though.
And it only will idle if cold; most of the time when it is hot it will either idle at maybe 100-300. Usually it just shuts off.
Anyways, as far as I know my older brother (whom I bought the car from) said it only overheated once because the radiator cap was bad or something. Then he ran it too hard/out of coolant and it overheated again. I haven't overheated it since I've owned it and because of the apex seal problem I fill up the coolant everytime I leave anywhere because it is usually empty or close.

Also, I don't know that it is a cracked apex seal but all the symptoms are there... I also have to drive this car; I've got no other form of transport.

 

If you let it idle and it dies out relatively quick you might have blown a seal. That's what happened to mine.

 

Why do you think a cracked apex seal would cause over heating?

Overheating would be caused by the water seals (completely different than apex seals) going and letting engine heat into the water jacket. For this you should check for bubbling coolant. And the more times it has over heated, the more likely the seal is to have gone.

If you actually blew an apex seal, you would not have any compression or ignition on two faces (could actually cool the engine down) and would experiencing significant power loss. By significant I mean that you would not be able to move without at least 50% throttle. You would not be able to idle without significant throttle adjustments.

Like any engine, you should do what people have suggested above, check compression, check fluids, check spark plugs, check sensors (TPS), and probably should consider taking off the intake manifolds and seeing if an injector has been stuck open.

 

The turbo II engine I am using for my vert project, 4 of the 6 apex seals had corners that were chipped away. If I can find them, I should post pics. My builder kept them to show me. He asked if it was still running, which it was, but it ran like crap with a very irratic idle. It had other issues too....vacuum leaks and such. It was removed from a parts car, so I was happy it was still buildable.