Hi everyone

I have a strange issue on my RX-7 FD.
The engine is mainly stock 13B-REW, it was rebuild by myself a few years ago.

When I driving the collant fluid is going through the overflow on the surge tank, until the low water level lamp is on and the beep too, with engine temp rising.
If I wait for the engine to cool down I can add one or two liter of coolant.

At first I was thinking of an issue with waterseal, exhaust gaz going in the coolant circuit pushing the coolant fluid out.
The car was set aside for several months and now I want to diagnose the problem and correct it.

When I tried to mount an exhaust gaz detector on the filler neck I noticed a strange behavior : the coolant fluid is going up in the detector very quickly, almost no gaz but only the coolant.
So I made the bubble test with a bottle and I can see the coolant going up over the filler neck very quickly without any bubbles.
Here you can see a video right after the startup, as you can see on the PFC commander the engine is cold so it's not coolant heat expansion.


And the coolant is still going up in the bottle until filling it.

Here is a test with reving up the engine mid-heated (around 45°C), no bubble at all.


Does anyone have any idea ? I can't figure out what's pushing the coolant fluid without any bubbles

Thanks for you help

 

You may not get many bubbles until the thermostat opens up. From what you've posted, it looks normal so far.

Try getting a bigger bottle and seeing if you can run the car until it's up to temp for a similar video. (Something like this: )

 

thanks for your reply.
I'll try to let it run until the thermostat opens and see whats happens.

I'll tell you after.

 

You can also run down to a local parts store and see if you can rent a coolant system pressure tester. Pressurize the system per the FSM and see if the pressure drops. If you cant find the spec online, let me know I have the FSM at home.

 

manuals can be down loaded form the foxed.ca website:

Foxed.ca - Mazda RX-7 Manuals

 

Ok, I found some time to do the test you suggested.

Here is how it went.

At first the engine temp was rising and the level in the bottle too.
When reaching around 72°C (I guess when the thermostat start to open) the engine temp displayed on the commander was going down ! Until 62°C.
When I saw it going down I tried to rev up the engine and here is what happened :


As you can see : big bubbles, coolant level in the bottle is going down (as expected with the air going out of the circuit), some foam...

So, waterseal problem right ?

 

Probably.

Assume the coolant hasn't been changed recently which would introduce air in the system

Another check is to see if the spark plugs are showing signs of coolant. Are they wet looking. If it's really bad, water may come out of the spark plug holes when you turn the engine over. Also, does your exhaust smoke

 

I have no smoke on the exhaust and no leak from the coolant circuit to the housing. Only pressure going (I guess) from the housing to the coolant circuit.

 

Usually a leak will work both ways, combustion gases getting into the coolant and coolant getting into the combustion housing. You can try a leak down test which will pressurize the system on the coolant side with no opposing force on the combustion side. That should show 1) if you are holding coolant pressure (which i doubt) and possibly 2) where a leak may be. If it's the seals, you should see coolant at your plugs since the engine wont be running to burn off the coolant. If you don't immediately notice signs off coolant on your plugs after the test, turn it over with the plugs out to see if the rotors push any standing coolant out the plug holes

 

Actually I dont have anything to put the coolant system under pressure with a gauge.
I'll try to find one around me or online, in the meantime maybe someone else will have more information with my last video posted.

Thanks for your help

 

The OEM thermostat opens around 82 C. I would check and replace with OEM if you have an aftermarket or unknown thermostat. Those temperatures you posted are odd. When bleeding air with a funnel I idle until the theromstat opens and fans cycle a few times (they are set at 90 C on my car).

 

I have a low temp thermostat, but whatever the opening temperature I should not have bubbles.
I'll mount an electric water pump later but first I need to diagnose the current problem before going futher.

I repeat it's not a bleeding problem, It happens when I drive : the upper part of the coolant system is filling up with air, pushing all the liquid on the road through the surge tank overflow and at some point the low coolant level alarm lights up.

 

I dont think is your water seals, there is no qay you lost that much coolan for the car not to blow white smoke.
The over heating happens when you have AC on or it doesn't mater?

Sound like if the system is clugged/no circulating somewhere, but where the bubbles come from.?
Maybe bad waterpump. I have to know what you find.
As you sure know this diagram is from big fat cooling thread.

 

I had the same problem. My issue end up when I replace my radiator. It was a small coolant leak. I was never able to see it cause one it was regulará driving temp, the heat would evaporate the leak before it landed on the ground. I also did the pressure text and it came out good. I even boubght the coolant bleeding kit from oreilly and it get some bubble but not all of them. After I replace the radiator I found out the best way to purge the system was to drive it and top off the coolant after each drive.

 

Some news

It was a waterseal I guess.
I bought a bottle of K-seal and after using it no more bubbles even after a hot session.

Thanks all for your help

Now I can mount the shakebomb garage electric pump kit to avoid anymore over heating and preserve the seals