Coolant burning in exhaust (heat exchanger)
12-26-14, 12:52 PM
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Coolant burning in exhaust (heat exchanger)
Hey guys,
It's been a long time since my last post, glad to be back.
My dad's '80 RX-7 just started smoking - it's definitely coolant, and it's coming from the junction between the air duct ("head pipe") and the lower air pipe that leads back into the thermal reactor.
If left to idle for a few minutes, it will actually drip a small amount of coolant from where the pipe is clamped to the exhaust. Once the engine is up to temp, it dumps a fair amount of white, sweet-smelling smoke from this area.
I do not get any significant smoke out of the tailpipe (other than a puff at startup).
My question is...WHY DO I HAVE COOLANT HERE?? I'm trying to figure out how the air pump and air control valves work, and if they may be leaking oil into the system. I'm stumped on this one...thanks!
Here is the smoke:
This is where it's coming from (not my photo)
Here's a more complete view of someone's exhaust system (not my photo)
Here's a diagram of the system:
It's been a long time since my last post, glad to be back.
My dad's '80 RX-7 just started smoking - it's definitely coolant, and it's coming from the junction between the air duct ("head pipe") and the lower air pipe that leads back into the thermal reactor.
If left to idle for a few minutes, it will actually drip a small amount of coolant from where the pipe is clamped to the exhaust. Once the engine is up to temp, it dumps a fair amount of white, sweet-smelling smoke from this area.
I do not get any significant smoke out of the tailpipe (other than a puff at startup).
My question is...WHY DO I HAVE COOLANT HERE?? I'm trying to figure out how the air pump and air control valves work, and if they may be leaking oil into the system. I'm stumped on this one...thanks!
Here is the smoke:
This is where it's coming from (not my photo)
Here's a more complete view of someone's exhaust system (not my photo)
Here's a diagram of the system:
12-26-14, 02:12 PM
#2
That pipe is supposed to feed hot air from the heat exchanger forward to the air injection ports below the rotor exhaust ports. (these are the two small black holes you see in the thermal reactor flange, below the exhaust ports.)
On the bottom drawing, it's basically the section of pipe with the white "up" arrow that leads to the dotted-lined passage under the thermal reactor.
Coolant there would mean that you have coolant coming into the combustion chambers. Since the air-injection ports come in from the bottom of the exhaust ports, coolant would collect there first, rather than in the main exhaust path.
Two main ways coolant can end up in the combustion space: either a water seal between the side and rotor housings is failing (which means a rebuild) or a coolant o-ring between the intake manifold and the keg is failing (replaceable by removing the intake manifold & carb).
First thing I would do is replace your radiator cap; if the cap is not opening to allow expansion when the engine is shut down, you can get overpressure in the cooling system that forces coolant past the seal. Plus, the rad cap is cheap and easy to replace.
You should see the coolant level in the overflow tank go up once the car has warmed up, and it may rise a bit after shutdown. Then when the car cools down, the level should fall. If that doesn't happen, the rad cap is bad.
If that doesn't help the next least-invasive action would be to replace the intake manifold gasket and o-rings. Not terribly hard or expensive, and may solve the issues for you.
The third possibility is that the water seals between the engine sections are leaking. This usually means a rebuild is required, as the only way to replace those seals is a complete bench teardown of the engine.
Some people have had success with the aluminum-based leak-sealant additives, but I've never used them myself. Probably falls under the heading of "might help, depending on how bad the leak is." & definitely cheaper and easier than an engine rebuild.
Once you've solved the coolant leak, then you need to fix the leak in the air pipe; if water can exit there,then air leaks under operation too.
Good luck.
Oh,and PS; make sure first that coolant isn't just leaking down onto the pipe from above, soaking that fiber insulation, and then getting boiled off as the pipe heats up. Given the pipe's position, coolant leaking from the intake manifold o-rings or possibly even the upper rad hose/water pump could possibly run down the engine and end up dripping onto it.
On the bottom drawing, it's basically the section of pipe with the white "up" arrow that leads to the dotted-lined passage under the thermal reactor.
Coolant there would mean that you have coolant coming into the combustion chambers. Since the air-injection ports come in from the bottom of the exhaust ports, coolant would collect there first, rather than in the main exhaust path.
Two main ways coolant can end up in the combustion space: either a water seal between the side and rotor housings is failing (which means a rebuild) or a coolant o-ring between the intake manifold and the keg is failing (replaceable by removing the intake manifold & carb).
First thing I would do is replace your radiator cap; if the cap is not opening to allow expansion when the engine is shut down, you can get overpressure in the cooling system that forces coolant past the seal. Plus, the rad cap is cheap and easy to replace.
You should see the coolant level in the overflow tank go up once the car has warmed up, and it may rise a bit after shutdown. Then when the car cools down, the level should fall. If that doesn't happen, the rad cap is bad.
If that doesn't help the next least-invasive action would be to replace the intake manifold gasket and o-rings. Not terribly hard or expensive, and may solve the issues for you.
The third possibility is that the water seals between the engine sections are leaking. This usually means a rebuild is required, as the only way to replace those seals is a complete bench teardown of the engine.
Some people have had success with the aluminum-based leak-sealant additives, but I've never used them myself. Probably falls under the heading of "might help, depending on how bad the leak is." & definitely cheaper and easier than an engine rebuild.
Once you've solved the coolant leak, then you need to fix the leak in the air pipe; if water can exit there,then air leaks under operation too.
Good luck.
Oh,and PS; make sure first that coolant isn't just leaking down onto the pipe from above, soaking that fiber insulation, and then getting boiled off as the pipe heats up. Given the pipe's position, coolant leaking from the intake manifold o-rings or possibly even the upper rad hose/water pump could possibly run down the engine and end up dripping onto it.
12-26-14, 03:11 PM
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Perfect, this is EXACTLY what I was looking for. I had actually come to a very similar conclusion on the coolant pooling at the base of the exhaust port and draining backwards towards the heat exchanger.
Entire cooling system (radiator, thermostat, hoses, cap, etc) was replaced last year and is working great. Coolant reservoir level rises and falls with engine temps just as expected.
Obviously I'm going to start with the intake manifold gasket and o-rings. I'm going to try to stay away from any radiator leak-stop additives...I'd rather fix the problem at the source than patch it up. If that doesn't fix it and the issue turns out to be an engine rebuild, then so be it. It would be a great opportunity for a full-blown refresh, porting, removal of emissions/air pump crap, and headers and exhaust.
Thanks so much for the help, this is great information.
Entire cooling system (radiator, thermostat, hoses, cap, etc) was replaced last year and is working great. Coolant reservoir level rises and falls with engine temps just as expected.
Obviously I'm going to start with the intake manifold gasket and o-rings. I'm going to try to stay away from any radiator leak-stop additives...I'd rather fix the problem at the source than patch it up. If that doesn't fix it and the issue turns out to be an engine rebuild, then so be it. It would be a great opportunity for a full-blown refresh, porting, removal of emissions/air pump crap, and headers and exhaust.
Thanks so much for the help, this is great information.
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