Hey,

I was driving my full stock 93 FD on the highway yesterday, for 2 or 3 hours at a normal speed (130 kmh / 80 mph) under a VERY hot sunny day... I have my window stuck closed, so I wanted to have another try with my AC (I knew it wasn't really working though) and switched it on. 2 seconds later I heard a BIG impact noise, kind of metallic, coming from the engine. I immediately switched off the AC. Then, 3 minutes later or so, I got the "add coolant" beeper and light on. So, I stopped the car. There was some white smoke coming from under the engine (coolant burnt I guess), at that point I'm not sure but it seemed that the radiator fan wasn't turning, at least I didn't hear it. I checked the fuses, all look OK. Anyway, I let the car cool down for one hour or so. Then I checked the coolant level in the Overflow Bottle : full. I removed the Thermo Housing Cap (no pressure at all) : Empty. I started to fill it with coolant, when I found out just a couple seconds after, that all the coolant I was adding (more than 1L) was already on the ground, still dripping from the middle bottom of the radiator. There is a huge leak somewhere fore sure... but I couldn't from where.
I called my mechanic, for him the impact noise I heard after enabling the AC is normal and not the cause of that problem, just a coincidence... (I have serious doubt on this, since it happened clearly right after) and he thinks it should be a hose failure (I hope so), or the radiator.
The thing that I don't understand is why all this happened right after I enabled the AC... what link between the cooling system and the AC ? (which was out of service before)

Let me know if you have any ideas
I will check in the engine bay and from under as soon as possible. I've read some post with similar problem ( https://goo.gl/pSEyAT ), so it may also be a water pump gasket....

 

Put a radiator pressure tester on it and the problem will identity itself. I don't think the ac is related as its not really relevant to any other systems. If you still have the stock plastic radiator, it's possible that it just exploded and that's the noise you heard.

 

thanks for your reply !
Yes, it is the stock radiator. I've only managed to take those few pictures of the bottom, but I can't see an explosion evidence from this point of view.




I don't have a radiator pressure tester but I'll see if I can borrow one from someone.

 

Regardless of where the leak is coming from, you need to replace the radiator with a good aluminum radiator as well as the AST (if it is stock) and replace all the hoses while your at it.

You may also have a blown coolant seal if you were driving around without any water in your engine.

 

Ok, well I lifted up the car but I didn't notice any broken hose or leakage point. The radiator bottom hose is OK.
So I ask a friend to pour some coolant in the thermo housing, and after a couple seconds the coolant appeared from the top center of the radiator and sytarted dripping on the ground. I took this photo :


I didn't notice any other 'path' from which the coolant was coming.
Does this look like an exploded Radiator ?

I still need to remove the air box to have a better view from above and check the top radiator hose. (which is often the one that break, from what I've read)

TomU : I really hope you're wrong about the coolant seal...
About the radiator, it may be a good idea, indeed. But, I attach a great importance to keep my car the most authentic as possible. Can you recommend a good aluminum radiator that looks like a OEM one, and is really 'drop in' ? I really want to avoid any other modification to fit it in. I read some posts about the fluidyne, sold as "drop in" but in fact, not really ! ^^

 

It's likely that radiator is done. That could be coming from the core and running down or coming out of a split in the end tanks. The only way to verify is either use the pressure tester or remove the radiator and fill it out of the car. As far as aftermarket replacements, I think all of them will require just slight modifications. Koyo, fluidyne, mishimoto, any will work.

 

Since the coolant leaked from the top after adding a little, It's likely the engine is OK since you didn't run it out of coolant.

IMO, the stock radiator is fine, but doesn't have an infinite life. If you can still get a new one it'll likely last another 25 years. I replaced mine along with all radiator and vacuum hoses back in 2006 as a preventive measure.

 

Alright, thanks for your comment.

I've just removed the air box and intercooler to have a better look from above. I expected a big hole in the plastic top of the radiator, but it doesn't look so obvious (to me) if it really exploded. Even the upper hose looks alright.





Maybe just some 'metal wings' in the middle of the radiator (red circle in the photo) look really bad :


...but according to the big metal impact noise I heard, I really expected something bigger... Anyway, I will pour some more water and check if it leaks from there or not. And then I'll remove the radiator.
I would love to replace this radiator by another OEM stock one if I could find one new, I've searched but they seem totally unavailable
And I'm also looking for a OEM style intercooler, as mine looks not very fine too... but for now, I only find front mount or V-mounts intercooler.
Finally, I found out that the Intercooler Cross Membre Support Bar is almost cut by the rust at some point (the yellow circle in the photo), I definitely need to replace it as well !

 

IIRC, most radiator failures have occurred in the joint between the core and the end tanks. The crimped joint weakens with heat and age, and the seal is lost. You are likely to find a section where the crimped aluminum looks loose and/or slightly deformed. That will be the failure point.

 

the radiator plastic starts black and fades to brown, and then white with age. while its doing this it also gets really brittle/fragile.

just based on radiator color alone, that radiator should have been replaced a long time ago. someone had the upper hose off at some point, its not the factory hose clamp, but they didn't change the hose (you can see the imprint of the old clamp)

also you need to make sure the fans spin freely. i saw one where a piece fell of the battery box, and jammed the fan, which let the car overheat.

one of the things with the FD is that every part can fail, so you need to check every part. there are a few, like the turbo water hoses, and headlight lids where they just need to be replaced periodically.

 

Just a side note. In one of your first pictures you show the car on the tow truck with the under tray removed. I'm not sure if you removed it for the pictures or you don't have an under tray. If you don't have an under tray you are greatly diminishing the cooling capacity of the radiator and the AC condenser.

 

That makes sense, and if it ruptured that would fit the explosion type sound.

Agree 100%. In 2005-2006 I replaced the radiator and all the rubber parts in the engine compartment. Since then I haven't driven it much, so maybe I'll have to do it again in another 10 years.

 

Alright,
So I've tested it when still mounted on the car, and it seems that it's really broken and leaking from that part (red circle in the above photo)
But, nothing to notice from the top/bottom plastic tanks.


We don't really see the water dripping in this photo so I shot this video :
Youtube video of this Radiator Leak

I removed it, and it's definitely looking so baaad :





I can't understand why my mechanic didn't tell me it was that bad when he rebuilt the engine just before it happened (actually all this happened when I was coming home from the garage after this rebuild, still breaking in)
He told me that I should change it in a close future, but when I see how bad this radiator looks like I think he should have told me before putting it back on the car... and changed it immediately before letting me drive it like that...

Anyway,
j9fd3s >> Thanks for all those tips !
The fans spin freely, yes ! But, indeed, some of them have some wear signs on the corner... at least, they should still be working fine, nevertheless, I will change the fan if I can find one to go with my new radiator.

mdp >> There wasn't the undertray when I bought the car , and this incident happened when I drove it back home for the first time...
Anyway, thanks a lot for this info ! It's the same for my mx-5 actually, but I ignored the FD had one too ! I discovered it when I read the FSM yesterday.
I'll buy one if I can find it ! (any tips ? ^^)

 

I'm wondering that since there was no undertray, that maybe something bounced up from the road and damaged your radiator. That would account for the loud noise you heard, and could have caused the leak.

 

you should check the fans (there is a fan test port in the diagnostic box, i think), and if they work, they are fine. if you need new ones, the 99 spec fans are probably easier to get, as they were used on a couple other cars, they are also a small upgrade

 

Good idea, thanks !
unfortunately I wasn't able to find any post or info about a fan test port on the rx-7
I only found this FSM page which is already a good test, even if a test port would have been a lot easier

 

well, I just stumbled upon the DaleClark's Fan system post and noticed this :
( https://www.rx7club.com/3rd-generati...system-906142/ )

so, could it explain why all of this happened to me right after I enabled the AC ? Since I was driving at 80mph, under a killing sun and heat, I don't know if the fan needed their high speed though ?

I know the damages on my fan look like an object bounced from the road (as DaveW commented above), but it seems so weird to me that it happened in the seconds right after I enabled the AC switch.

 

If I had to guess, it looks like something has been dropped into the fan shroud, which upon selecting the AC on - the fans fired up and caused the damage evident to the radiator and fan blade tips.

 

Also worth noting - if you didn't see it or no one else noted it - your fan has a big chip out of it.


When you replace your radiator, go ahead and replace the fans too.

You can go with the 99Spec Fans OR a set from an RX-8 (which you can probably get from a junkyard or used on eBay/RX8Club). I'm not sure if there is a difference between the two, but both are newer, include more fan blades (5/7 for RX-8 vs 4/5 for the USDM models) and are a bolt in to the USDM fan shroud. Make sure you get fans from the 2011+ RX-8 as they include the same four wire connector as the USDM model, however, please note repinning of the connector is required.

Here's a good write up on it:
https://www.rx7club.com/3rd-generati...x7-fd-1085155/

OH! An DON'T TOSS OUT THE OLD RADIATOR - you'll need the mounts from it for an ideal install on the new radiator.

-M

 

That makes sense ! Seems like a possible theory to me.

I've ordered a new Radiator, upper and low hoses and the intercooler cross membre support bar.
Meanwhile, I'll check the engine block for any wear (water seals...), remove the AC, heal and paint the rust on the chassis sides
and clean the overflow tank, as it really needs it :



And if the car is fixed with the new radiator, then I'll change the AST, the IC, most (all) of the hoses, and of course put an under tray (seems hard to find)

 

Thanks a lot !
I didn't know about the RX8 compatibility ! very useful because I didn't find any oem replacement.
Though, in the meanwhile, I've tested my cooling fans with the diagnosis box, and they spin flawlessly ! So, I don't know if it's really worth it. Maybe

 

Not sure if it's a typo, but its 2009+ RX8 fans you are looking for. All the series II RX8s have the 4 wire fans.

 

I installed the RX8 fans just recently. Indeed, you have to get the 4 wire version. They are a little quieter, pull more air, and use less amps. I painted them black on the outer casing to match the shroud and prevent rust. The wiring is easy. Just splice the wires to the old connectors after leaving enough old wire to solder in the new wires.The wires match color for color. I bought the motors and fans brand new from Mazda. With the usual 33% discount, the motors were around $55 each and the blades were slightly more, around $75 each. You could get new motors and used blades which would make it cheaper. Also, I cleaned up the plastic shroud and painted it with Eastwood black plastic trim refinishing paint. Everything looks brand new and works perfect.
Mike

 

Get A Koyo or Mishimoto aluminum radiator. The Mishimoto is easier to fit with a stock setup, but is lower quality. Koyo has more capacity and is a higher quality unit. With the mishimoto you will need a 5/16 to 3/8 barb adapter because for whatever reason the made the bottom nipple too small.

N3R1-15-150 are the RX-8 fan motors you want. They are much cheaper than the RX-7 fan motors and flow more. You will need to remove the connectors on them and transfer the rx-7 fan connectors.

The FD fan blades don't fit on the RX-8 fan motors. You need the following:
RF1S-15-140 right side
RF2A-15-140 left side

 

One correction from my post. I checked and I did pay $55 for the motors but around $100 each for the fans.
Mike