I've noticed a slow leak of coolant from the top of the engine as it cools down. It hardly leaks at all when the ambient temperature is high (like in summer). It seems to come from somewhere between the thermostat and the alternator, but very difficult to access. It starts at the very front of the engine block and then flows down a slight slope (perhaps because of the position of the engine or the car). I've changed the water pump and re-sealed the large pipe from the radiator to the engine. Do you have any idea where this is coming from? Thanks

 

That is the intake coolant seals leaking. You'll want to remove the intake manifold to fix this.

Keep as many bits attached to the intake manifold as you can. Do not remove the carb by itself. There are four bolts and two nuts that hold the intake to the engine. Remove the bolts that attach the rats nest to the top of the engine without remove the the hoses from the carb or rats nest. The idea is to keep the intake/carb/rats nest as one unit. Believe me, if your not familiar with RX-7 and all the hose routing, this is the easiest method. There are also some exhaust connections to the intake along with the air pump. Those can be removed individually.

You'll want to buy a new intake gasket and the o-rings for the water passages in the intake.

This will need to be fixed because it's leaking while driving but going up as steam. Left unchecked, you'll start seeing steam in the exhaust and the coolant level going down.

 

Don't you think it would also have a collant puddle on the floor if leak coming from the intake manifold? Anyway it seems to be a big part to remove (with the carb included) I am quite familiar with the RX but not with mechanics (whether rotary or not ; )

 

What he's telling you is true. This is a well known issue amongst those who do understand the mechanical of these cars.

 

The coolant will puddle on the housings and if bad enough or left alone long enough, will begin to run down the front or rear of the engine and create a small puddle on the floor. Typically, the coolant will just be noticeable on the housings in the recesses in between the intake manifold and the housing or housings.

 

You mean that even if the intake manifold seal is located lower down on the engine, the coolant leaks on the top of the engine anyway? It is due to some temperature/pressure calibrations or something ? Sorry but I am not an expert

 

It really not that much lower.

Here is a picture of the intake manifold and gasket. Looking at the two round opening, those are the coolant passages and have a rubber seal to prevent leaking. What happens is that the rubber o-rings fail and cause this puddling. Remember this coolant is under pressure so it doesn't care which way is up or down. If there is a compromise, it gets pushed out.

The engine pic is not a 12A but does show the coolant passages.

 

Is it that part for the 12A?

 

What you posted looks to be a gasket for ther thermal reactor to engine for the 79-80 12A.

 

Depending on the year of the 12A, there are two intake gaskets. The difference is the center port which allows exhaust to heat the intake. The 1979-1980 RX-7 12A, and before, intake manifold do not cover the port.

You also need to rubber seals for the water jacket openings. https://www.atkinsrotary.com/Mazda-G...27-13-113.html

I always like to put a very light amount of sealant over the entire gasket. A paper thin amount so that if you have to take it apart in the future, that gasket does not fuse to the intake or engine and can be reused if not torn up.

1976-1980
https://www.atkinsrotary.com/Mazda-G...3-13-111B.html


1981-1985
https://www.atkinsrotary.com/Mazda-G...1-13-111B.html



Intake rubber o-rings for water jacket. https://www.atkinsrotary.com/Mazda-G...27-13-113.html

 

O-rings can be had for way cheaper. if u have one that's in fairly decent shape, take it with you and check ace hardware or any auto parts store. they may have one that's very close to the same size. i've done this in the past.

and if u know a place that rebuilds hydraulics, try them. just a regular O-ring just metric size.

 

May be I can use the 81-85 gasket even though my engine is older. They haven't changed the engine structure in the meantime. They just added an extra inlet on the gasket to improve operation. Er, that's not a suggestion but a question.

 

The 1979-1980 still have the center square exhaust opening, it's just not covered by the intake manifold and instead open to air (the internal port is a little different but no concern here). You can use the 1981-1985 gasket. Just cut off the extra using your old gasket as a template.

 

I've got to start taking things apart. Do you know if I can find a step by step tuto
to remove the intake manifold on Mazda rotary engines with a carburetor?

 

There isn't really a good "How To" in the factory service manaul, just general "remove carb" type of stuff.

Here is how I do it.

1. Disconnect the battery terminals.
2. Be very careful around the back side of the water pump housing. The temp sensor that controls the choke is there and that wire will break just by looking at it.
3. Take a bunch of picture before and during disassembly. If you need to remove a part, take a picture first.
4. There are two/three small bolts that hold the rats nest vacuum manifold (metal part) to the top of the motor. (10mm bolts). You might need to remove a couple of the things to get to tem but don't go crazy. Try not to remove any vacuum lines.
5. Do NOT remove the rate nest vacuum lines going to the carb. There are a few line the cruise control and vapor canister you will need to remove. Take pictures first.
6. Remove the hot strat, throttle, cruise control cables from the carb. This is a little harder. It's hard getting your hands in position to put slack on the linkage but I've done it many many time. I like to do some from the passenger side. The hot strat is easy.
7. Remove the air pump
8. Remove the four bolts and two nuts that hold the intake manifold to the motor. A swivel joint and small extension helps. It can get very tight and your working by feel. You can also remove the exhaust manifold to get more room but try not to if you get help it. If you need to replace the exhaust manifold gasket that's another story. Remove the exhaust manifold first then.
9. Take pics of each electrical connector you disconnect form the carb.
10. When reinstalling the intake gasket, I like to put a very small skim coat of sealer of the gasket (both side). This helps preserve the gasket incase you need to take the intake off because of an issue. Don't forget to install the rubber o'rings.
11. Then tightening the intake nuts/bolts, don't go all monkey on them and break a stud/bolt.

I know I've probably missed something but this is a start. Have a question during this just ask.

 

That's where I'm at right now. The carburetor is removed, and you can see where the coolant leak is stagnating. What do I remove now? In particular, the part I pointed out.

 

Remove the intake manifold. There are two bolts and the top corners on the intake. Then there are two bolts and two nut. The bottom ones are near the top of the exhaust manifold. It's kind of a feel thing. This is where the wobble extensions come in handy. The intake gasket above will give you an idea of where the nuts/bolts are to remove. You'll also have to take off the air pipe on the rear of the intake.

Do not take the nut off that you are pointing at.

 

Okay. In the meantime, the final part has been removed. So here's my gasket and o-rings...
seemed to have taken a weird shape. I will update progress of the work soon.

 

The only way I can think of how those o-rings warped and that gasket condition is massive heat or a fire.

 

i'm keeping you informed of the progress of the repair. Everything has been dismantled and reassembled. . but after a week, no leaks found.
By the way, do you have any advice on choosing a starter battery? This type of engine seems very demanding. My usual battery is sufficient for my other engines (but no diesel) but with the rotary the battery has no power left after two or three unsuccessful attempts to start it. Maybe it's worn out. But what should I change it for (amperage, voltage, suitable diesel...)?

 

No leak at all after those weeks. So we can say that the issue is fixed.

 

I like Optima deep cycle batteries.