I have question. Please refrain from the coolant seal is gone. I have a different problem.

I lose about a cup of coolant every 3 to 4 days which equals about 120 to 160 miles.

I always have pressure in hoses. overflow doesn't bubble nor overflow. water pump neck cap off, no bubbles, foam nothing. Pulled plugs always dry, no water in exhaust or coming out.. no smoke ever not even start up.

I have replaced every part in the coolant system. Do I have a coolant seal that could be only allowing coolant inot combustion chamber only during hi rpms and doesn't reverse pressure and push coolant...WTF!!!

I have RX7s for over 16 years. I want to say its leaking into the combustion chamber, but no proof of this.

Compression is perfect, and coolant pressure tester shows no leaks.


ideas?

Thank you.

 

Well...? I'd still say maybe a hairline crack somewhere.
Sounds like you've already been doing everything correctly.
Why not tear down the engine and have a look?

 

I know I should rebuild it, but its running low 14's on street tires. I really think the car would be slower with coolant leaking into the rotors housings.

 

do you ever smell any vaporizing coolant?
I had a similar problem, only I would smell coolant when I punched the gas. Turned out to be a bad clamp on the heater core hose that 's directly over the tranny bellhousing. But a pressure test found that out.

You have no signs of leaking coolant anywhere under the car either?

 

Never anything under the car, or on either of the 2 aero trays underneath.

Never any smell, I get a nice burnt carbon/gas stink after a good 7K rpm pull.

How can I lose coolant and still maintain pressure in coolant system?

Thats impossible right???

car always starts right up, never any issues.

 

do you ever get a nice film on the inside of your windshield? lol, nevermind a cup of coolant every 4 days would be one thick *** film!

 

You can still have good coolant pressure with a leak. even a small leak will still dump a lot of coolant over time. Maybe it is your heater core like tex said. notice any wet carpet?
but on the other hand a cup of coolant every 4 days, you would probably smell that.

You have to be losing it out of your overflow tank then, if everything else checks out. You said you pressure tested it and it didn't drop any pressure at all? how long did you let the tester sit after you pressurized the system?

 

The car is dry inside, and behind the carpet, under both seats.

No the over flow tank stays exactly where I fill it too. I have pulled the overflow cap and looked to see if bubbles come out from the hose under coolant, nothing.

Now this is the odd part. I forgot to say this and this is why I think its a leak, but a odd one.

When the coolant system ends up low, it will not pull coolant from the overflow.

however pressure stays with the tester for about 4 to 5 hours, then down a
little then stays solid for at least overnight.

I also just replaced my water pump as one day I noticed the weep hole leaking. I assumed this was the cause of my loss of coolant, however no water stains at home or work, so I caught it the day it started..lucky me.

Once replaced water pump, I have higher volume pump from Japan. Same loss of coolant, and its not really much over 160 miles in 4 days, with speeds over 120 mph on the interstate.

 

you kno i had the same problem then the next morning my car wouldnt start pulled the plugs out thought it might be flooded come to find out my engine lost all compression over night somehow.....wow gotta love these rx7's!

 

You gotta love these 7's when they do crap like that.

 

You have a leak that is not apparent under pressure, but leaks under Vacuum. This happens to RX7's pretty frequently. When the engine cooling system cools off a vacuum is formed. The vacuum pulls the coolant back in from the overflow tank. If you have a leak that allows air to come in during this time, the coolant does not return and stays in the overflow tank.

The problem is even harder to find if you have used some sort of stop leak material. The pressure during operation forces the material into the leak stopping any coolant from coming out. Under vacuum however, the material gets sucked out of the leak and air enters the system.

Likely places are a leak in the hose from the radiator to the overlow tank, or bad connections at either end of the hose.

A new oem rad cap is pretty important in this situation as well.

My leak was actually a hairline crack in my S5 thermostat housing.

Good luck.