Rad Cap hissing
 

Just got a radiator flush and fill, car had sat before I got it and it had "sludge".
got it home and the radiator cap is hissing. No bubbling, just steam hiss. Can't see it, just hear it. Temp gauge is normal, cap seems tight. Should I be worried about pressure leak and overheating on a longer drive? Blew my AST up previously because of a weak seam and loss of pressure. This was only a 15 min drive btw.

I'd go ahead and replace the caps.

Stock you have a pressure cap (on the AST) and a flat cap (on the thermostat housing). Do you have an aftermarket AST now or did you eliminate it?

Use Mazda caps, parts store caps are typically crap. The Mazda caps last a VERY long time.

BTW the spring cap should be wherever the hose going to the coolant overflow tank is attached.

Dale

Aftermarket AST now...metal, so no more plastic stock 27yr old pieces.
They both have spring caps, no flat caps. Came that way.

Which one was hissing?

A spring cap instead of the flat cap is fine, done that before. Big thing is you don't want a flat cap on the neck that has the overflow tube, that causes big time problems.

Also what AST do you have?

Dale

It's a custom built no name AST. Buddy built it, engineer.
the hissing one is on the Radiator, not the AST.

And the AST has the overflow tube, forget to answer that.

https://cimg4.ibsrv.net/gimg/www.rx7...48b9996f93.jpg
This is hissing

Excuse the mess,,the AST blew up over everything.

Few things from the picture -

First, that big hose on the left (the air pump to air box hose) is really pushing into that hose going to the AST. Also you have clamps everywhere on that hose, I would get that put together properly and make sure that AST hose is in good shape and not leaking.

The aluminum base that cap is attached to is really rough looking, may want to clean that up and make sure the cap is sealing on that well. I would also be certain that you don't have an air pocket in there from swapping the AST.

I'm thinking it could also be having a pressure cap there, it could be water pushing up against the cap to the top part of the cap. May be worth getting a flat cap.

Dale

I'll give it a shot. Bought someone else's problems, tying to sort therm out.
weird thing is, it didn't hiss prior to the flush. Hoping a leak didn't form causing pressure issues

i've also seen little bits of gunk get on the sealing surface of the cap, so make sure those are clean.

https://cimg4.ibsrv.net/gimg/www.rx7...bfe06a574d.jpg
🤔

There ya go!

Dale

Well,,,may or may not had been the cap. Overheated AGAIN, popped the hood and the hose from the filler to AST blew right at the neck....probably an original hose that deteriorated....
replacing and seeing what else can go wrong.

If that cap with the broken seal is off of the place pictured, it appears to be a pressure cap. You should have a flat cap in that place, and a pressure cap on the AST.

May be worthwhile to get a pressure tester and see if you find more leaks, bad hoses, or worst case internal.

If the car is overheating, stop driving it and sort out the problems. Do a coolant system pressure test and fix what's wrong. Don't guess at replacing random parts and use a test drive to find the next leak. That will cost you an engine.
Ray Crowe will sell you a full coolant hose kit. Suggest you budget for that now and replace them. Get the OEM hose clamps while you are at it as the ones in the pic are done. The OEM hose clamps will fit better and won't loosen up over repeated heat cycles like worm clamps.
This has been discussed in various threads on the coolant system in the past. You can find links in the FAQ thread.

It's a much bigger issue than hoses turns out.
https://cimg9.ibsrv.net/gimg/www.rx7...713435dca3.jpg

I wasn't test driving. I had been driving it no issues, since I fixed the fuel pressure problem. It just started overheating after my coolant flush. Found the cap and put two.and two together. So there wasn't issues prior to to be concerned about. Then the hose blew and when I replaced it I found this nozzle all corroded. Just trying to get home now to fix everything.

Wow that hose nipple is DONE. I don't think I've seen one that bad!

You have 2 options on that nipple -

- It's a steel nipple pressed in to the aluminum thermostat housing. You can cut it off/drill it out, tap the thermostat housing, and screw in a hose barb that's the appropriate size to fit the hose.
- Get a good used thermostat housing. They shouldn't be too hard/expensive to track down.

I would for sure replace that AST hose and maybe the other AST hose that goes from the AST to the radiator. Get new Mazda parts for both and they will last a VERY long time.

If those hoses are bad you may want to look over all the coolant hoses and see what's due for replacement. Or just go all in and replace them all, I think Ray Crowe was selling every single coolant hose for like $120 at one point.

The hoses easily last over 100,000 miles. Also Mazda updated the rubber in the hoses at some point so the newer hoses are better than the original factory hoses. Don't try and use some parts store generic hose, they WILL fail on you.

If you're buying a cap anyhow I'd probably buy the flat cap, it's cheaper I think anyhow. Doesn't really make a difference performance-wise if there's a spring or flat cap there.

Dale

Just got my hoses...for anyone looking...they are $210 now..
and a new housing, $85

That's not too bad on the T-stat housing. Where did you get the parts from? That makes a big difference on the price.

Dale

Ray... I added gaskets and a 90° hose in the order, made up some.of the $210

Cool, yeah Ray gets the best prices on parts. Should be a happy car with all those new parts on it!

Dale