My coolant has leaked from the overflow tank twice now when I shut the car off on a pretty hot day (80F+). It's leaking from the top plug on the main portion of the overflow tank that connects the line going to the AST. It's a new overflow tank that was installed before I bought the car. Is this a symptom of a bad cap on my filler/AST, or do I just need a new plug/line/overflow tank?

I haven't had any issues with over heating but I'm still running the stock temp gauge non-linearized so it's not a ton of help.

Here's a bit more info that may help:

I flushed the coolant and changed it to a 30/70 mix when I got the car a month ago. I changed out the oil, filters, plugs and wires. The plugs were pretty charred up and I estimate it has been some time since they were changed.

I live pretty far back in a neighborhood so I drive with no boost for about 2 minutes then let the car sit for a few minutes before turning off after a drive. The leaking starts, as far as I know, after I shut off the car. Which makes sense as the overflow tank starts filling at that point (as far as I understand).

On cold starts I do get some minor puffs of white smoke at starts especially if it's been sitting a few days. Not a major amount, but noticeable. Stops when warmed up. Compression tests when I bought the car were within minimum mazda specs, I think ~95 psi for both rotors/all seals. I haven't had any problems with hot or cold starts.

Sorry for the long winded post, hope the info helps.

I never did get a chance to post where I'm starting from so here a few pics to attract would-be board stalkers. This is my first rotary and FD. I really appreciate the help and info these boards have provided me over the past month of tinkering and learning. Here's some eye candy after a good wash and wax.

 

Hi there, does it actually overflow out the top of overflow tank or does it just leak from somewhere around that area?
Check the entire length of tube that runs from the AST to the overflow tank. (not just both ends!)
If that tube has a hole in it or isnt connected properly with a tight seal (mine even had a join half way along it, dont know if thats standard or not) - it will prevent the engine from sucking the coolant back in from the overflow tank when it cools down / the coolant contracts.
This in turn can cause your overflow tank to overflow (as coolant gets pushed into the overflow but does not get sucked back into the engine under vacuum)-
Or you may intermittently get the low coolant buzzer going off after startup.

 

Start by inspecting/changing your cap on the AST, even though it looks new in the pictures. Look for any leaks in the coolant system, then you could have the system pressure tested. There is also a hydrocarbon test that can be performed to determine if there are exhaust gases in your coolant which would be an indicator of a bad coolant seal.

You need to get the level in the overflow tank down to a maintainable level, if you look on the dipstick, only 2" is full. Siphon some coolant out otherwise it will continue to overflow.

 

most likely the AST cap it can get little bits of stuff in the pull-back flap part not creating a seal and it will overflow after shutdown but not during running and no overheating if had it happen a few times usually just clean up the feed-back and good to go.

z

 

I went ahead and siphoned out some coolant from the overflow tank. I'm about 3 notches away from full so hopefully that will help. Refilled the filler cap so I don't get the coolant light. I'll update when I can take it out, weather here sucks right now. Non stop rain for months it seems like.

My damn AST cap is stuck on there pretty good, I'm going to have to rip that thing off. I've tried prying it off by hand and it just does not want to come off. I suspect it is indeed the culprit.

Before I do take it off, I want to make sure I have another close by. I don't know the manufacturer of the AST that is currently on the car. I've been in contact with Pettit to see if their cap will fit my AST. If anyone knows a better solution, please let me know. I really don't want to buy another complete AST kit. I'm trying to sneak some pennies away from the wife for a PFC.

I've attached a picture of where the leak occurs. You can still see some shine of wet coolant.

 

I'm probably stating the obvious, but you have tried pushing down while unscrewing the AST cap right?

 

I had the same problem early this month. I had an old AST so I replaced that plus the three hoses that connect to it and the two radiator caps and the problem went away.

 

That looks like a petit AST. I had one of those and it used to **** me off because at least one of the barbs was too small for the hose and used to leak.

 

Yeah I have. That thing is stuck on. Still waiting to hear back from Pettit to see if they think their cap with fit it.

I intend on doing this when I get word on the cap. Where did you get your caps from? I've seen lots of varying prices online and several different versions.

 

my solution..... delete the AST. If you have a 2 piece t-stat cover, then it's a breeze with the proper FC mazda part.

 

Oh I forgot. I didn't have any coolant leaking problems today, but it was cooler outside and I didn't get on it as much as when it leaked. I've relocated a temp probe to the throttle body coolant line and will connect to a gauge tomorrow. I hope to get more accurate temps, until I get my PFC.

 

I got the ast, radiator caps, and two of the hoses from rx.com. I got the ast to overflow line from autozone.

 

I finished install a coolant gauge in the TB line to allow for more accurate temps. My caps are ordered and should come next week. I also went ahead and got a 180 degree thermostat to help. I'll post again after everything is installed and I've taken it out on a hot day.

 

Agreed. Delete that POS.

Mine car did that for a long time and the temporary fix was to change the caps. I got tired of constantly doing that so I deleted the AST and the problem finally disapeared.

 

One more vote for deleted AST. I got the FC filler neck from Ray at Malloy Mazda. The install was really easy since my car came with the two-piece filler neck /thermostat housing. More info here... http://www.fd3s.net/coolant_tank_elimination.html


An even better solution would be to add a true 'expansion tank' as found in many newer cars. Expansion tanks are larger than the RX-7's AST, are always mounted at the highest point in the cooling system, and intentionally contain air in addition to water. Since air is compressible, the system pressure stays more consistent even when the coolant expands and contracts due to temperature changes. Packaging this in an FD's engine bay would be pretty difficult, though.

 

I do have a 2 piece t-stat cover so it should be a breeze to switch it to the FC neck.

Since I already ordered the new caps, I guess I'll just temporarily fix the problem as you described. If I can make it through the summer I'll rip the AST out and put in the new thermostat when winter rolls around.

I was doing some reading over on fd3s.net on AST deletion and the consequences from it. I know this has probably been discussed over and over again (I'll get off my *** and search when I get some more time). Since it sounds like all you guys have it done, what are the drawbacks for doing it? Have any of you had any strange results from it?

 

The AST function is to trap air in the system. So if you delete it all you have to do is make sure you burp your coolant system correctly. FYI-I have not suffered any ill effects from the deletion.

 

You have a Pettit AST. I had one, and had problems similar to yours. The Pettit AST is made of aluminum, and bends easily. After replacing several caps, I discovered that the sealing surface on the top of the AST was warped. There was no way it could have a good seal. I replaced it with a new AST from Tri-Point Engineering. Problem solved.

 

+1

I experienced some of the same issues, and like I mentioned earlier the nipples don't fit quite right (too loose) which leads to leaking.

got a RE-A one and haven't had problems since.

 

Update: For the moment the new caps seem to be doing the trick. But I will revisit this once I experience the problem again and most likely rip out the AST as many of you suggested. Thanks for all the comments.