1993 FD RX7
Fully stock
Good compression (105)


I've had my 93 RX7 for the past several months now, its just starting to 'overheat'. Once its turned off it will dump water around where the over flow tank is. Even though the gauge is reading normal, don't know if the sensor is faulty, or theres something else happening.

The other day, it was at the normal temperature, stopped to fill it up, it dumped coolant (add coolant light wasn't on after), tried to turn the car back on, wouldn't even spark (guessing now that the ecu wasn't allowing the car to start because it was too hot) eventually turned on the gauge went straight to the top, then went back down to normal 5 seconds later. Confused on how it gained a significant amount heat once it was off? Drove it home with no problems, ran great, no smoke. Turned it off, then back on, started straight away and temperature was ok. Hoses etc look like they're in good condition. Unsure if its a dodgy thermostat, there is rust in the coolant (so could be clogged), air trapped in the system. Really unsure what the problem is, if there is even one.

Haven't found any threads with a similar situation, so any responses will be greatly appreciated.

Cheers

 

Hate to be the bearer of bad news, but search 'bad coolant o-ring testing procedure.'

 

A friend's FD had the same problem just the other week. His pressure cap on the AST went bad, so the system wouldn't build pressure as it heated up and just dumped out the overflow tank.

Replaced the cap and no problem after that.

If you think the thermostat is bad, I would just go ahead and replace it now too. It's just a few bolts and a coolant flush which never hurts for these cars. Make sure you burp the coolant system when refilling. The lisle funnel works great for that.

 

I would bet that you need a new cap on AST. The spring and or seal is probably worn out and allowing pressure to push coolant to your overflow.

 

Hi, thank you for the replies. The previous owner appears to have gotten new caps, so I can't expect they've gone already. But I can see that the pressure is escaping somewhere in the depths.
And for the o-rings, I think it's unlikely to be that, but still to play it safe, I'll probably get it tested to see if there is carbon dioxide in the coolant.

 

Reading thru your first post, my first thought is that you absolutely need to add an aftermarket temperature gauge. The stock gauge is not linear. That means that from something like 150 F. to almost 240 F. it will sit at it's "normal" position. But if it ever moves up, it's almost always too late and the car has seriously over heated. So it's worse than worthless.
Second thought is that you need to establish WHERE the coolant is coming from. There are other things in the general area of the overflow...turbo coolant lines, heater hoses etc. If it IS coming from the overflow then it's not really a good sign. Read through here with special attention to post #9 and the symptoms I listed..... https://www.rx7club.com/new-member-r...oblem-1032258/

 

So my guess now is that it is probably the o-ring, theres a lot of pressure building up in the system and it dumping the coolant straight into the overflow, which is then leaking out the top where the hose connects. Fun times

 

 

Definitely get an aftermarket gauge, even a cheap one. The standard temperature gauge is nest to useless.

 

Shouldn't this be the opposite? Know you can do either or on the filler, but thought AST should always be pressure cap.

But yes, as others have said, get an aftermarket gauge, and do a flush. The sign of rust is what worries me.

 

I stand corrected, thank you. And yes...ON A STOCK SET-UP, the filler neck will have the cap WITHOUT the spring, the AST will have the spring cap. You can put a spring cap at both locations, but that is how it is originally.
In my defense I deleted the AST several years ago so only run a spring cap on the filler neck. Sorry.

 

Just got it tested, and yes there was carbon monoxide in the cooling system. So one of the o-rings has gone.
Thanks for everyones comments.