I have done a search this morning on here for help, but all its done is make me more worried!!

Had service done last Mon, asked to replace radiator cap, as rubber seal had swelled and clearly wasn't sealing properly.

Car had been forcing the top pipe to pop off the AST and chuck coolant out, but only after a run. Had to fill it when starting, as coolant buzzer was coming on. Puddle underneath car where AST is too. Car starts on the button every time, hot or cold, which I think (hope) is a good sign, ie seals not gone on engine! It has about 30k on WGT rebuilt engine, never driven in anger really. Thought that problem was caused by rad cap leaking.

Which pressure cap should be on the main filler and which on the AST?
The AST had a 0.9 one and a spring, the other didnt have a spring, but don't remember pressure. The replacement one i have now is a 1.3 with a spring, but it was put on the AST and the AST (0.9) one was put on the main filler. Should they both be sprung?
All was fine on way home. Next day coolant buzzer goes off soon after starting up.
Noticed caps were wrong way round and have swapped them over. Should I have? Noticed steam coming from left headlight area after shutting down. Middle pipe to AST coming from rad filler had come off, even tho it was clamped!! The pipe coming from the bottom of the AST is also weeping a bit. It is chucking out about 500ml of coolant, as that is how much it takes to fill it to normal level (about an inch down filler neck, just below the small hole down there).

Car drives fine, boosts fine, starts fine etc, this is really worrying me now tho. Have to do it nearly every day now..... If the seals had gone it wouldn't be chucking it out the ast would it? The place that serviced it also said that the rad could be blocked because the fans were cutting in and out within about 2mins while it was sitting there, indicating that it was getting pretty hot, pretty quick!! Any ideas anyone?

EDIT: PS Car is a standard '96, not even got a catback on it! Not got PFC so can't see exact temp.

 

Sounds like a plugged line to the overflow tank if it is blowing off. You might have other problems, too, but blowing the overflow line off seems like a clear sign that it is pinched or plugged. Fix that first and see if you still have trouble.

You need a cap with a spring on the AST. The other cap can be plain (no spring), but I don't think it hurts to have a spring cap on there.

-Max

 

Thanks for that.

Which line goes to the overflow tank, the one coming out of the right hand side as you look at it, or the one from the bottom of the AST? They haven't blown off over the last few days but I'm still having to put coolant in. There is steam coming from that side of the car, underneath the AST.

It could be the line to the overflow tank I guess, but I've not got the tools with me to take off the intercooler duct to check, as I'm at work!

I turned it on with the main filler cap off, and the level stayed pretty static, which I think is a good sign? How long would it take before bubbles/any water movement would occur generally?

Also, AST cap 0.9, main cap 1.3 right?

 

The main cap is 0.9. Stick to the oem springless one for the main btw. Ray Crow from Mally Mazda gave me a great deal....13 bucks I believe.

 

Thanks, but its a bit of a long way to go to order a radiator cap!! I live in the UK!

So the 1.3 is too high? Sure that was what was on there before, just not a spring version....

 

1.3! That's 19lbs, take that cap off. It's too much pressure for the coolant system. The system can only take 20lbs max, and that's for testing purposes only. You should only have a 13lb (.9 bar) cap on the AST tank, and just a cap on the main. 19lbs. on an old coolant system and you're asking for failure.

 

The 1.3 bar one is on the main filler cap, I do have a 0.9 on the AST, although the guy who did the service put them on the wrong way round. So I have a 1.3bar on the main filler and a 0.9bar cap on the AST. Surely having the 1.3 on the main filler is no worse than having a normal (ie non pressure rated) cap?

 

1.3 is too much pressure for the main one.....mazda went from a 1.3 to 0.9 in 94 I believe.

 

FD Coolant System 101

The "main filler" cap has NOTHING to do with pressure relief. NADA. It should have a non-spring cap. It is just for filling.

The cap on the AST is the pressure relief cap. If more that 0.9 bar of pressure builds in the cooling system, the spring valve in the cap will allow coolant to be ejected from the system into the overflow tank via the top hose right at the top of tha AST neck. The coolant cap also have a small reverse valve in the center (that's the little metal disk on the bottom) that will allow coolant to be pulled back into the cooling system from the overflow tank.

Look at the cap. Apply the brain to the problem. Understand how it works.

Preventing overflow by going to a higher pressure cap IS NOT A FIX. You need to understand why the system is not operating correctly and fix the real problem.

First thing that you need to do is to make sure the overflow hose is not clogged or kinked. You should be able to disconnect it at the AST, blow into it and make bubbles in the overflow tank. Please don't swallow the coolant, it is poisonous.

If the line is not clogged, then you need to start looking other places. Post back here with your results.

Good luck,

-bill

 

How old do you think I am? 8?

 

Neither of those hoses go to the overflow tank. The hose right under the cap is the one that goes to the overflow tank. The pressure in the cooling system overcomes the spring in the cap, and it pushes coolant out the cap and through that hose into the overflow tank. Then later when the car cools down, it sucks the coolant back into the engine through a one-way valve in the bottom center of the cap. If the coolant is getting pushed out but not coming back, you will lose coolant. If the vent hose is popping off, it sounds like it is plugged. But it could also have a hole in it, which would prevent coolant from being sucked back into the engine. The overflow hose can't be plugged or have holes -- the system won't work if it does.

To check if the overflow/vent hose is plugged, remove it from the nipple that is right under the cap on the AST and blow into the hose. You should hear bubbling noises in the overflow tank. And you should be able to blow into the hose.

-Max