rx78

I have had my 93 fd for about a year. I have not driven it much, engine has about 60k miles on it. About 10 months ago it overheated and shot out coolant everywhere and i thought i was screwed. Put a new thermostat on it and problem solved.
Last week it did the same thing. I discovered the coolant cap was no good and replaced it and the thermostat once more. (turned out it was clogged up) I let it run for 10mins after filling the coolant up and no problems. Then i found a video on the "champaign bubble" test. So the next day i took the cap off and started it cold. It would very slowly over flow and have a few bubbles in it, not much. After about 7 mins it is overflowing alot more, another minute and it is shooting out, breathing in and out. The car is still at normal temp and not overheating though. I have had my mechanical check for any external leaks, none are found. Took it for a 10 min drive and it acted perfect, thought nothing was wrong. Then it started heating up to the first line so I take it home and shut it off. Im thought maybe my coolant seals might be bad. However, there has never been any smoke or smell from my exhaust, which i researched is the sign.
So it overheats after 10mins of driving, no smoke or smell. As if this has anything to do with it, i find it odd this happens right after spending tons of work adding AC to the car. Is it worth putting Bars Leak into it?

Any ideas on what else there is to check? Any and every bit of help is appreciated.

gracer7-rx7

iTrader: (16)

Where are you located?

Don't put Bars Leak into it until you determine someting like that is actually needed.

I'd start by reading the Coolant system info threads in the 3rd Gen FAQ to learn about other factors. It sounds like the coolant system has been neglected and needs some help. Start with a pressure test to find any leaks and fix them. Find a rotary specialist near you if you can to give it a look.

Bad Coolant seals are commonly misdiagnosed.

rx78

Im in Houston, TX. My mechanic did a pressure test and there were no external leaks. I think we found the problem though! As I said my coolant cap was worn out and the rubber seal fell apart, so it was pushing everything into the overflow. So I went to Autozone and got one of those nice pressure realease caps. Sometimes it would do the same thing and push everything to overflow, lose water and overheat. One time it shot the spring up and water just started coming out from around the cap. After doing some more research I found out that the cap that goes over the coolant isn't your typical radiator cap, even though I think it holds the same ammount of pressure. You have to put a flat filler/pressure cap on it that has no spring. You cant buy them locally any where. Mazda wanted $45 plus shipping. I found one at Mazdatrix.com for $33 total. Should be here in a few hours and hopefully solve the problem!
Ill give an update after trying her out!

P.S. My mechanic had already decided to put Bars Leak into it before we found out about buying the new filler cap, hope it did no damage

wthdidusay82

iTrader: (15)

Are your fans properly woking?

Im not familiar with fds but if your engine fan isnt working the way it should because it went out, it'll definitely cause overheating.

My old 88 rx7 had a bad clutch fan and i didnt know until i ruled every other possible problem out.

flatules

not sure the Bars will bother anything, just graphite as I recall. Could always just flush the system to be safe. Just a head-up I found the cap .9 bar Stant cap at O Riellys for $10 bucks.

E.

wthdidusay82

iTrader: (15)

I wouldn't use anything but oem Mazda stuff.

gerald m

IMO if there a surge tank on the car then you can't close the system with out problems with expansion etc. even with no surge tank you still need a spring loaded cap to release pressure when it gets to great or you will blow hoses and **** . be careful sounds like you are creating more problems . Also if the thermo has gunge on it then you need to clean the system and start over Gerald m

Sgtblue

iTrader: (16)

*Drain and flush your coolant system completely. Get that damn Bars Leak out of there. That means draining the radiator as well as the block. There is a drain plug on the left side in the middle iron. Download the FSM for more info.
Refill with as much DISTILLED water to coolant as you can get away with in Houston. I think 70/30 would be fine.
*Replace BOTH caps with OEM and make sure they're both .9 bar.....NOT 1.3 bar.
*Check the face of your radiator behind the A/C condensor and make sure it's clean. Seems obvious but it's often overlooked. Then get some cheap upholstery foam. Cut appropriately sized pieces and plug any gaps around the radiator.
*Search the term FC Thermoswitch. It turns the fans on at a threshold temp of 95 C. vs. the stock 108 C. Not an easy job, but not THAT difficult.. and very worthwhile.
*Clean the face of your oil cooler(s) and straighten any bent fins. Could be tedious but not difficult or expensive. If you have a single oil cooler, consider at some point adding a dual cooler system from a 'R' model.
*INSTALL AN AFTERMARKET TEMPERATURE GAUGE IMMEDIATELY. I recommend the throttle-body coolant line for the gauge sensor. The stock gauge isn't linear and therefore worse than worthless. Then check the operation of your fans at all speeds. ---> http://www.fd3s.net/fan_test.html
*Be sure the "belly pan" is present and installed properly. Something else that seems obvious but...

Driven233

iTrader: (1)

This.

The rest of what Sgt said is great advice as well but the FC thermoswitch will be the best ~$60 you will spend for your car. Do a search it is not all that hard, just remove the alternator to get to it and a slim swivel wrench will save a lot of headache.

rx78

Thank you so much for your kind help! I will get on it right away. I got my new .9 filler cap and it worked great for about 25mins. Got on the highway and punched it, even made a Lightning cry after a race Then when I was pulling back into my neighborhood,
It steamed and spewed out of the coolant reservoir on the left side (left if your looking at the engine) I filled it up with antifreeze last night and drove it today and it got to the overheat guage mark twice while driving, but would go right back to normal after 10 seconds. Then eventually it was done for the day. When I pulled over it wasnt spewing from the same place. This time it was coming from the small "air pressure reservoir?" Thats attached to the airduct. I'll drain everything again and check on what you suggested.
Just wandering if the fact its coming out of a different reservoir means I fixed one problem by replacing the filler cap, but still have another unsolved problem.
One last thing I'd like to get an opinion on. Check out this pic. Heres my new .9 filler cap. When I bought this car it had this Overflow Assembly on it. I know that is not stock, it doesnt have an overflow stock. Would it make a differance if i bought an OEM replacement with no overflow?
THANKS AGAIN!

Sgtblue

iTrader: (16)

That's an S5 FC filler neck. Commonly used when the AST is deleted. I doubt it has anything to do with your issues. I have one on my car.
STOP driving the car until you find out why it's overheating. As I said earlier, the stock gauge isn't linear. If the needle has moved past about 9:00 o'clock, it's overheated and may damage the coolant seals....if they weren't bad already. Those WOULD be responsible for your symtoms and will require removing the engine and, practically,rebuilding it.

rx78

Thanks sgtblue, I drove it once after getting my new filler cap to see if anything was wrong. still overheated and after taking a look around i noticed that a hose came off. Going to put a new clamp on it, see what does. If it overheats once more Ill follow your steps: fc thermoswitch, check radiator, look at the oil coolers, and replace the guage. when you replaced your guage did u just buy a pillar assembly?

rx78

Was it a flat cap? I havent seen any in stores any where. just in case anyone else is reading this, I think i heard that the Stant brand has caused trouble for rx7s for some reason.

Sgtblue

iTrader: (16)

^It should be a spring cap with the FC filler neck. And again, I strongly recommend the OEM .9 bar cap.
The only other thing that comes to mind is making sure that the small bore hose running from the filler neck to the overflow isn't plugged or kinked. Coolant expands as it's heated by the engine and runs into the overflow thru that hose. When the engine is shut down things begin to cool, a natural vacuum is formed and draws coolant back out of the overflow tank into the cooling system. That line is a thin-walled hose by design and can kink a bit easier than others. If it's plugged, kinked or blocked in any way by something pressing against it, that will disrupt the vacuum and the ability of the system to draw coolant back out....eventually the overflow tank/reservoir would overflow.
The other common cause of an overflow reservoir doing that is a failed coolant seal.

Yes. FWIW I use a single 'A' pillar pod with a Defi 'D' series temp gauge. The sensor is in the throttle-body coolant line (search for more info). That line is easy to acccess and gives accurate readings. I now have a PFC and can also monitor it on my commander, but I'm old-school and still like to use the gauge.

rx78

[QUOTE=Sgtblue;11176561]^It should be a spring cap with the FC filler neck. And again, I strongly recommend the OEM .9 bar cap.

I did order a Mazda OEM .9 bar cap, it is a flat cap though. Your saying I need to order a .9 bar cap with a spring since I have FC filler neck? Cause the picture I put up of the FC Filler Neck has flat .9 bar cap on it too. Sorry if Im repeating myself, Im just very worried and never had a project car.

Drove after I clamped the hose, which was from the air reservoir (attached to the airduct) to the coolant reservoir, and it still over heated. I will check the filler neck hose tonight. Next I guess I'll run some tests on the radiator, its aluminum. Going to see if certain spots are hot/cold and hopefully find a clog.

***OK just got NEW news from my mechanic, whos amazing, but never worked on rotary before. first let me say when I got this car nothing under the hood was put together correctly, and tons of parts were missing. I just got the AC working and put that air reservoir (whatever its called) thats attached to the airduct into the car. (never overheated before i put in this air reservoir) That air reservoir has a hose that runs to the radiator, thermostat housing, and the coolant reservoir. The FC Filler Neck has an OEM .9 bar flat cap, and the overflow hose from it is capped off and does not go anywhere. **From your statement that over flow hose should not be capped off, and go to the coolant reservoir? (which is why I would need a spring cap correct?) I dont think I have this car put together correctly!! Sounds like my hoses are in wrong places!

*** PLEASE ADVISE!

-Once again thank you so much for taking time to help me!

MIBagentQ

iTrader: (3)

https://www.rx7club.com/3rd-generati...thread-571088/



With all of this overheating, I don't understand how its possible your car is still alive!

RotaryEvolution

iTrader: (30)

by the sound of it compression is being pushed into the cooling system. replacing the pressure cap on the surge tank several times should have yielded some sort of result but pressure is obviously building up and venting out of the system. from where? i think we know where.

there was no need for an FC filler neck, that is for people who are eliminating the AST and running the nipple off the FC neck to the overflow tank directly. if your hoses feel rock solid when the car is warmed up and it's pushing coolant into the overflow regularly then you are pretty much screwed.

Sgtblue

iTrader: (16)

Yes, that FC filler neck should have a .9 bar SPRING CAP. And yes, that nipple on the FC filler neck should have a hose leading to the overflow bottle. I'm not sure what an "air reservoir" is...unless your referring to the AST (air separation tank). If so, then personally I recommend you delete the AST, plug the nipple at the bottom of the radiator and the old metal nipple on the aluminum thermostat housing just below the filler neck. You don't need both the AST and that FC filler neck, and since you probably don't have the original filler neck, go ahead and get rid of the AST.
If you have both I agree the previous owner was....confused.

If it helps, this is what it should look like. In the picture I removed the old metal nipple and put in a brass AN plug.





There is nothing inherently different about the FD cooling system from any other piston engine car.

rx78

This is the only pic I have of my engine bay at the moment. This is how it was setup when I bought it. AST deleted, FC Filler neck with spring cap. No AC
I just went through hell finding all of the AC parts I needed, and got it running. At the time I didnt even know what a AST was, (thanks for teaching me the propper name!) since I didnt have one on there. I just saw pics of 7s online and thought, hell, I need to get that on there. Got an OEM AST, OEM flat cap, and the next week I got this overheating problem.
I just recently deleted the AST, put the spring cap back on, and have it hooked back up the same way the pic shows, hoping it would stop overheating....it hasnt...
The fans I have in there are not stock/OEM. It was in a wreck from previous owner, and they obviously bought some cheap *** fans and didnt bother hooking them up right. There are two connectors/wires that and hanging down there that I believe are from the stock fan setup. They dont even kick on when you turn the AC on. So if I buy new fans and thermoswitch the car should stay cool, and hopefully not overheat.

But...where the hell are the air bubbles coming from??? Its not that many bubbles.
Plus after research and your answers, everyone says that if there is even a small coolant seal leak, the car would be hard to start, and it would leak water from just sitting over night. My 7 starts the first try, with the key or remote start, and the water level has not gone down after sitting for two days.

Thanks Again! People helping others they dont know like this is amazing! I hope I'll be able to help people out once I learn more!

rx78

so its been a while guys, i put off trying to get it fixed for a while. I took out the thermostat yesterday and drove it for 40 mins, no over heating or water coming out or anything. all is running good. wanted to get some feedback from yall to see if youve ever ran your 7 without a thermostat, and if I could encounter any problems driving without one.
Thanks again.

Sgtblue

iTrader: (16)

Running w/o a thermostat allows a considerable amount of coolant to return directly back to the engine and by-pass the radiator completely.

In your initial post you said you put a new thermostat in and it didn't help. I doubt that was your problem then, and I doubt running without a T-stat will cure the issues you had for very long. Something else is going on.
There were alot of suggestions in this and the other thread you started. Eventually I think you'll have to try them.

rx78

I just cant figure out what it is. I dont think my seals are bad because it starts up just fine and it sat for a month and when i checked it out, no water even leaked out for a whole month. All hoses are good, the radiator is good too. The only thing I can pin point is that it has after market fans, and the only problem with them is they dont kick on right away if you turn on the AC, which is no big deal to me. The only thing i havent done is replace the fans or get a fc thermoswitch. Any other ideas? Im just so excited to drive it since i took the t-stat off!