I have a 93 RX-7 that is losing coolant from the overflow tank. The engine was rebuilt only 13k ago. I've replaced the coolant cap, and it still loses enough coolant that the buzzer goes off every third time run the car. The engine doesn't get above 175 deg. I pressure tested the system and it held 24 psi for over 24hours with no coolant in the rotor housings. I replaced the coolant lines thinking there was a blockage. For test purposes I removed the Air Separator Tank and installed a filler neck from an 88 RX7 that has the overflow nipple so I could connect the overflow tank. No difference in how quick I lose coolant. There are no visible leaks anywhere. There is no reason I can find that the cooling system isn't pulling coolant back from the overflow tank. I even pressure tested the cooling system while the engine was running to see if it was building pressure and it doesn't build pressure. At this point I'm at a loss. Can anybody give me a direction to go in?

Thanks

J

 

I'm about 3 hours from you... if you are bored over the weekend, bring it by and we'll figure out what's wrong with it. Have you used an emissions sniffer on the filler cap to see if you are venting any exhaust into it? Exactly how much coolant are you losing per hour with it?

 

what pressure cap did you put on ? my car was doing that too because the replacement cap pressure was too high. iirc it was 1.3kg and i put a .9kg cap on and all is fine now

 

I replaced it with the stock .9kg. I've been told to bump up to a 1.3kg to fix it but I haven't picked one up yet.



Thanks for the offer of me driving up. I'm headed out of town for the weekend but if I don't get it fixed soon I'll take you up on the offer. No, I hadn't thought about the sniffer in the filler neck yet. I'll look into it. As far as what I'm losing is about 16 to 24 oz. every 3rd start up which is usually around 40 to 60 miles. I'm not sure of how much I lose per hour or miles on a single drive. I usually refill the same amount every trip out. I usually have to empty the overflow tank about every 100-150 miles. That's usually about 6-8 start ups/drives. The system acts like it loses vaccum and doesn't pull the coolant back from the overflow tank when the car is cooling down.

 

I know you said you replaced the "coolant lines"...did that include the line from the filler neck/AST to the overflow tank?

I know it's a long shot, but that particular hose seems kind of flimsy...just a single wall with no reinforcement of any kind that I can tell. Maybe it's collapsing under vacuum as the engine cools?

 

my problem was the loose clamp that goes on the filler neck. barely loose. it leaked when hot/pressure built but was so small that coolant evaporated as it traveled down the hose(is that even possible). there were no drips, 99% of the times i checked it was dry...

 

Update, I found something that might be a problem. My car was dead cold and I started it for about 30 seconds and thought I needed to add coolant. After I shut it off and started to open the fill cap I noticed it had pressure on it. I gave the coolant hose going to the top of the radiator a good squeeze and it was full of pressure. I released the fill cap and it sprayed coolant everywhere. Question, can or should the system build pressure on cold startup that quick. 30 seconds shouldn't be long enought to heat the coolant more than a few degrees. So is the water pump building the pressure? Or maybe I have a coolant seal leaking on cold starts that's building exhaust pressure in the cooling system. If that's the case wouldn't the 24 lbs of pressure I tested with have leaked off over the 24 hour period? I'm at a loss on this one. Let me know what you guys think.

Thanks

J

 

Are you absolutely certain it wasn't pressurized before you started it?

It would be really unusual but I guess I could see a coolant seal failing in "flap" fashion, essentially creating a one-way valve. Holding pressure applied from outside while allowing combustion pressure to enter.

 

Yeah, I know there wasn't any pressure on the system since I was replacing the coolant filler neck the night before and this was the first time it was started.

 

I know of no other explanation for the cooling system pressurizing to that extent in just 30 seconds other than due to a coolant seal failure. But then I also have never heard of a cooling system holding pressure with a failed seal.