Sorry this is a long post, but I want to give as much info as possible in hopes that someone can help me. First off this car is an NA 1988 rx-7 convertible. It is stock besides a cat-back exhaust. I have the haynes manual. I also have the FSM. When I first got the car I drove it a mile or so and the low coolant light/buzzer came on and it started to overheat. I pulled over asap, but the temp gauge got to about 3/4 the way to H. We did a little diagnosis and I thought it was the thermostat. After we replaced it and a cap the car ran fine for an hour drive home, only having the low coolant come on for a second.

The next day I started it up and it gave me the same problem. I drove for about five minutes and the buzzer came on and the temp started creeping up, so I pulled it into my garage quick before it had a chance to get real hot like before. At this point I inspected the system. The coolant level in the reserve gets real high and even shot a bit out. The coolant looked old and rusty, even though the seller said he'd replaced it recently, but idk. I inspected the upper and lower rad hoses, as well as the line leading to the overfill tank. They all seem in tip top shape. I don't believe the thermostat was the problem and I put in the factory mazda thermostat. The upper radiator hose gets hot at operating temp so I believe it's flowing fine. The oil and filter were changed June 13th and it has a factory mazda filter on. The oil level is at the correct amount.

I drained the coolant and flushed the radiator with my garden hose. I drained the coolant in the block, but don't have a system to flush the block. At this point I examined the water pump a bit. I checked the weep hole and it was dry as the desert. I flexed the upper rad hose and it has pressure like normal. I don't hear any bad sounds coming from it either. I inspected the cooling fan. It seems in great condition, no chips or cracks, and seems to operate as it should. The rad cap was replaced.

I also did a compression test with my standard tester and found that the front rotor had 120 psi, while the rear rotor had 90 psi. After the compression test I forgot to plug the crank angle sensor so it flooded and I had to pull the egi fuse and run it and it smoked for a bit, but no big deal really. I inspected the spark plugs, they were a little blackened on one side, but just seemed a little older, still looked like they were in good functioning condition.

Other symptoms of the car that are important: The overfill tank seems to allow coolant to go into the tank, but never gets drawn back out when cooling. There is constantly bubbles of air coming into the overflow tank. When the car drove fine the other day the bubbles were not present during that drive. The car is able to reach operating temperature and doesn't get hot or give low coolant light while idling. Driving it seems to cause the problem.

It's possible that the system was not bled or burped properly. What I did was install the drain plugs, fill from the filler neck until the rad was full, installed the rad cap, filled from filler neck until coolant came out the bleeder hole, put in bleeder hole plug, filled until the coolant was up to the filler neck top and put the cap on. Then ran the system for 3 minutes with heat on high and allowed to cool and added more coolant to the filler neck.

There's been no record of any overheating problems with the car in the past. I saw the carfax and it has a clean record. When I test drove the car it had no problems and I pushed it hard to make sure. ANY help is greatly appreciated. Thanks.

 

sounds like a tired rear rotor. possible rebuild soon?

hmmm sounds like a leak into the combustion chamber. or a water seal cracked which is letting exhaust gasses tryin to escape through the cooling system.

i bleed mine with the engine off. just "massage" the hoses and leave the filler cap off so the bubbles can go out and have a jug of water near by to replace the air with water, or coolant, or a 50/50.

my 2 cents.

goodluck

 

i have the exact same problem also but i noticed my radiator had a small crack in it, my problem didnt start til i went out drifting like 4 weeks ago, my friend told me it could be a water jacket, so i drained the entire system and ran straight water and like heavy steam started pouring out of my exhaust for like 5-10 minutes, but the temp never even hit halfway, even after driving it around the neighborhood for a few. so idk even know what the problem is with my motor, ima try replacing the rad and see if that was the problem

 

do you smell coolant in the exhaust? you may want to consider a rebuild very soon.

 

i took a few wiffs of it and it didnt have a scent, when i was burning coolant and overheating like crazy i smelled it a little bit, i redlined it in front of a friend and he claimed he saw a little bit of fluid come out, after draining and flushing the system and replacing a water pump and thermostat and cap to make sure it wasnt any of those it stopped for a little bit. now the add coolant light is on 24/7 and the temp stays at about a quarter up from C, when i do a WOT pull the light goes off for like 5 minutes, i havnt driven the car for 2 weeks now, im goin turbo 2 soon anyway

 

I don't have the money for a rebuild right now. I'm not super intimidated by the idea, but it would be my first rebuild, so I don't want to if I don't have to. Perhaps in the future after I've learned more about rotaries.

I was also thinking it's letting exhaust into the chamber. I found this in the FAQ:

"I think my engine has been overheated. How can I check to see if the coolant seals are good?
Fill coolant system ALL THE WAY UP (engine cold). Make sure that the fluid level is as high as you can get it. Leave the filler cap off. Remove the EGI fuse. Crank the motor (it should not start). If you get a LARGE amount of coolant coming out of the coolant fill, its safe to assume your coolant seals are blown. Also, a good indication is a fuel/exhaust smell in the coolant."

So I did this, but barely anything came out. Maybe a capful. But I think the coolant might smell a bit like gas, it's so hard for me to really tell.

I also tried the bleeding method you mentioned. It seemed to remove some of the air.

Now the car wont start. It smells flooded again. I'm thinking I'm going to change the spark plugs. Which plugs would you recommend getting?

Is there any other way to diagnose the seals without opening the engine?

 

i hear ya there. i really need to be prepared for a rebuild soon, but i have this goal of hitting 200k before the motor quits. im almost at 170

I was also thinking it's letting exhaust into the chamber. I found this in the FAQ:

hmmm might be a tiny leak. you could also test your cooling system with a pressure test. you hook some thing up to where the filler cap is and it pressurizes the system and if there are any leaks they will show.

[QUOTE=EnjoiPugs;9328492]I also tried the bleeding method you mentioned. It seemed to remove some of the air.

Now the car wont start. It smells flooded again. I'm thinking I'm going to change the spark plugs. Which plugs would you recommend getting?

hmmm...uhh whatever spark plugs people recommend on the forum. haha sorry i cant be of much help there.

probably not.

 

A pressure test on the cooling system will diagnose this. If the coolant is going into the engine, a pressure test will force it in so you will see the level drop and then coolant will come from the spark plug holes when you turn it over.

It is possible to get such a small failure that it only shows up at operating temp and while the engine is running. In that case, a gas analysis on the coolant will help. If it shows hydrocarbons, there is an internal leak.

But always, check for external leaks first. A small external leak could just leak vapour and be very difficult to find.

 

Thanks guys. I am going to look into performing the pressure test and I'll post my findings afterwards.

 

Check the Hose going from the Rad to the Coolant jug.If that Hose is not Immersed in Coolant in the jug,it can't take coolant back in the system when it needs it.
check the Cap on the jug,and it's Tube to see if it Cracked.That is a common problem.It will allow the coolant to go Into the jug,but not Back to the Rad,if it has a leak.

 

Two things...

-Since you are having cooling problems, now is the ideal time to get a real temp gauge so you can get hard data- i.e., real numbers- instead of "3/4 to H" or "just over halfway".
Even the superior S4 gauge (compared to the glorified idiot light of the S5) doesn't tell you what you need to know when closely monitoring a cranky cooling system.
You can get a perfectly good VDO gauge and sending unit for @ $35 (I like egauges.com) and start dealing in facts instead of approximations.

-It's possible that there isn't a "magic bullet" fix for your problem.
In other words, more than one thing may be going on, each contributing it's own little shot of pain.
With a newly obtained car, my preferred method of dealing with subsystems (like cooling or brakes) is to take a scorched earth approach and replace everything at once...in your case, waterpump, thermostat, rad cap, hoses and belts.
If possible, do the rad itself as well (look at the Godspeed replacement, I was quite pleased with mine).

This approach may seem excessive but over the years I've found it's actually cheaper and faster than spending endless hours trying to diagnose a car that (at this point) you know little about.
It also gets your hands on lots of places (redoing the brakes is even better) and you begin to get a general feel about how the car as a whole is faring.
Also, afterwords you know that it's not something external to the engine that's causing the problem.

One thing that struck me in your original post was the inspection of the fan.
OK, good, the blades are in good shape, but what about the thermoclutch?
That's a far more likely failure point than the blades themselves and it's not easily diagnosed.
Now might be the time to consider a switch to an efan.

Now...get to work.

 

Thanks for the advice mistersty and clokker. I heard about the problem with the line leading to the coolant jug and I already inspected it. Removed the air intake tube and looked at the entire hose. There is enough coolant for sure in the jug.

I plan to get a real temp gauge soon. I totally agree, it will help out a lot. I want to get another radiator, but I have to wait until I start working again to get some cash. I really think the problem is the coolant seals in the motor. When I went to start it today it was flooded from nothing. When I cranked it without the egi fuse and got it started it smoked a lot at first. I smelled the smoke this time and it smells like coolant, I'm quite sure about it. I was thinking about trying one of those "head gasket fix" bottles you can get at autozone. I read someone else had success with this on here and I also used it on my old cavalier and it helped that car out. I'm going to look into it some more.