Backround-

So, I just recently picked up this car for 1000 because it leaked coolant and had some body damage. After a brief inspection after driving the car it was obvious that the coolant was leaking from the join where the radiator cap goes. Not from the cap itself, but the 'adapter' from the tube to the cap (sorry if this is a bit unclear, I don't know how to describe it too well). I had thought it would be an easy fix, after removing the 'adapter' there was a visibly worn o-ring. 62 cents later that was replaced. This slowed the leak, but only made it so it took longer for the pressure to build and force the coolant out of the same spot. After looking at my other rx7 (an 88 na) I saw that it had an overflow reservoir for coolant. $7 later that was added. Now, this setup appeared to work at first glance. I have been only driving this car maybe 1-2 miles each day, but as soon as I took it for a longer ride, maybe 4 miles the coolant buzzer goes off. Pop the hood, and the coolant isn't being forced out from under the adapter, and the reservoir is filling like it should. Get the car back home and as it cools down the coolant from the reservoir works its way back into the system like it should, but while running with the reservoir filling/full the oil temperature guage reads that the car is heating up considerably.

Any deas?

Is it possible that a 'bad' radiator could cause excessive pressure to build up and for the engine to heat up very quickly?

Have you checked the thermostat?



How does the car run? Any smoke pouring out of the exhaust when you start it up?

possible bad radiator my 86 when i first got it was overheating and i thought it was the motor so i pulled the motor and droped in a good working N/A replacement and did the same thing it was the radiator all along

Just replaced the thermostat (yesterday), I will let you know how that goes.

As for the smoke, yes, its fairly smoky at startup

As mentioned above, don't throw parts at it and hope it goes away. Unfortunately for him, he threw a motor at it and it still didn't go away, and THEN he replaced the radiator. I'll put money on it the radiator was a secondary failure of his undiagnosed primary problem, and he still has a problem somewhere in that perfectly fine old motor that got tossed.



It's possible for a radiator to clog, but chances are your building excess pressure elsewhere.



A quick flow test of a radiator - disconnect the hoses and run a garden hose water flow through it. If water comes out the other end, it's not clogged and it will not build excess pressure. You might not know if the radiator is efficient, but you'll know it's not clogged.



Now, do the same thing at the water pump inlet, and eventually the water should come out the outlet for the motor. Now you know the motor/t-stat house isn't clogged.



So, that portion of testing is done. Main system components that rely on no restriction to flow are: Radiator, thermostat housing, engine, and main hoses. Let's rule out the heater core for the inside of the car since it's a secondary component and any clogs will not impede flow (causing non-temperature related pressure).



How do we achieve pressure anyways? Pressurized water has a higher boiling point than unpressurized water. The rad cap's job is to dump coolant to overflow when the pressure is at a specific level, calculated to a temperature conversion since the pressure is consistant with temperature, since there is no real pressure being built in the cooling system, just hot coolant under it's own pressure from heat. I'm having a hard time explaining it but just bear with me.



Before you do anything, replace the coolant and bleed the system properly. Since you just drained the coolant and flow tested the rad and motor, the coolant should be all out and everything at this point should be OK. It's possible you had a pocket of air from all the messing around you've been doing. Refill the system properly and PURGE the air out of it. Then diagnose. If you don't have the correct tools to test the cooling system for pressure or rad cap, just replace the rad cap (it's like 10 bucks). Now:



Drive the car, monitor the amount of coolant in the overflow when cold and then hot. If it overflows uncontrollably without getting over 190-200 degrees F, then you have the answer to your smoking problem. Chances are there is a combustion/exhaust leak into the cooling system that's pressurizing your system and causing the rad cap to open and dump coolant into the overflow continuously, and replacing engine coolant with pockets of air causing the low light to flash and temperature spike. If this is the case the temperature will only spike when the temp sensor "senses" a pocket of hot air. If it overflows with NORMAL operating temperature, then this is likely the problem.





At the age of the car, a bad coolant seal is not uncommon anymore. And with the wonderful maintenace practices owners take with their cars, I'm sure that motor has seen some really whacked out pH mixtures from old coolant and some of the cooling system has sustained damage from it.



However, if you have purged the air out of the cooling system, replaced the rad cap, fixed the radiator o-ring leak, replaced the thermostat, and made sure the flow is not impeded, you probably don't have a problem by now if the motor is OK.





Ideally you would pressure test the cooling system with a pressure tester to see if the system holds pressure. If it doesn't you will see where the system leaks by means of the pressure tester forcing out coolant at the bad area, which can then be repaired.



See if you can get your hands on one somewhere, but if not, try the other stuff out. Report back.

my car acted all kinds of crazy.



the temp gauge would never go over half, but after a run it would pour coolant out uncontrollably out of the overfill tank if i left it idling.



and driving it normally, it would randomly coolant buzzer me after driving it, then letting it sit long enough to cool down completely.



i was stumped until the other day i accidentally leaned on one side of the filler cap, and coolant sprayed out of the other.

i havent had a chance to replace it though but im pretty sure that could be an issue.

That's normal, Lee. The pressure pushes the cap up slightly, and the O-ring still seats to hold the pressure in. If you lean on it, it can "tip" and unseat on the opposite side. Your cap is seating and holding pressure fine. A pressure tester can tell you if the cap actually purges excess at a specified pressure, or if it's failed it will just continually build pressure OR purge too early.



For anyone without a tester, it's way faster to just replace it with "known good", since a new one is pretty cheap. If you don't know how old it is and don't have a tester, and suspect it, just get a new one.



Just have to keep in mind the way this engine reacts to a coolant seal failure is completely different from a piston engine head gasket failure.



Lots of things are misdiagnosed before it's realized that a motor seal is actually dead. A dead head gasket sees intake, compression, combustion, and exhaust. A rotary can see any one of the four.



Imagine a bad seal on the intake side of the motor only. The rotor turning and the chamber expanding "sucks" intake air in, as well as coolant past the bad seal. You'll be missing coolant over and over without oil contamination or coolant contamination. Move the bad seal around the circle a little further, and it's in the compression side. Air is forced to be compressed, and some of the air and fuel is pushed past the bad seal since compression pressure far exceeds coolant pressure. You'll see pressurized coolant and NONE of the coolant is consumed, only blasted out the overflow from the compression pressure. Especially at WOT when compression pressure increases.



Combine this with heat expansion in an early stage of failure and the problem will only show itself until the motor is warmed up.

So, things had been going pretty smooth until today. I don't drive this car far since 1. i don't have to 2. i don't trust it yet.

I had taken it a little ways out of town and it managed to make it fine, coolant buzzer came on by the time i was just about home, though. but i thought nothing of it since the temp was normal.

Today i was running some quick errands (really didn't go far at all) had trouble starting it both times after my stops. Then on my last leg home i gave it a little bit of a sprint in 2nd gear. About a mile later my coolant buzzer came on, but i was 1/4 mile away from home, so i finished my trip. Stop, turn off the car, and i hear a loud hissing noise. Pop the hood and the cap from the coolant reservoir is hanging limp off of the tank. The hissing is from some sort of gas/pressure escaping from all the coolant goodness that there is in the radiator/running through the engine. Felt the cap and its completely warped, practically melted.... HELP!



*edit

I also want to mention that the coolant reservoir was a cheap one from a local autoparts store ($8) so it might just be cheap plastic that caused it to give...? (i hope)