turbox2

Anyone know why my coolant pressure would be up around 14-15 psi at idle (when it should be like 4 psi)? Mazda pressure-tested it cuz I was leaking coolant out the overflow on shutdown. No leaks in the coolant system. Not the seals either cuz I have zero smoke on startup, full compression, no water on the plugs, no hydrocarbons in the coolant, and no bubbles in the coolant. Mazda gave the car back to me and said, "Sorry, we don't know why the pressure's so high, and we can't fix it. You can have your car back now."

cewrx7r1

iTrader: (2)

The stock original Mazda coolant caps were about 16 psi. Something like 1.1BAR or ATM. They then went to a .9 I thingk. That would be about 13psi. Never down to 4 psi.

turbox2

So what would cause the coolant to be spilling out the overflow on shutdown? Like I said, I know it's not the seals. The coolant expands into the overflow when the car warms up, but then when the car is shut off, the coolant won't get sucked back into the engine and just vents out the overflow. Then I'm left filling up again cuz the coolant buzzer beeeeeeeeeeeeeps...

KevinK2

pressure will build to relief point soon after start-up, at idle, before engine warms up.

replace relief cap on ast, as check valve often leaks erratically. check for leaks in hose to overflow .... suck it up hose, plug end, and see if it leaks back to tank. purge all air out thru TB hose ... about 3 times, burp, etc. search burp, purge

RonKMiller

I guess the real question is: Is this supposedly "high"
coolant pressure causing any problems? Like - .....
overheating? Are you having to replace coolant all the time? Is your car hard to start when cold?

If not, I would not lose any sleep over it - especially if it was diagnosed by Mazduh dealership mechanics.

Sounds to me like the system is overfilled or you may have air trapped in the system, but WTF do I know........compared to Mazduh "mechanics". They are bonafide geniuses when it comes to a car they have not seen or serviced in ten years.

Buy an aftermarket temp gauge and keep an eye on it at all times. Never, ever take your car to a Mazduh dealership for evaluation. NEVER.

CantGoStraight

Unless you have a new .9bar cap on your AST these are exactly the same symptoms I had when the O-ring was failing. Replace the AST cap and take some of the coolant out of the overflow tank. If everything is proper (no air in coolant system) and cap is .9 bar (13psi) no leaks in hose between over flow and AST then problem should go away. If you keep pushing coolant out of the overflow, and have to add coolant after every engine cool down........well I'm pretty sure you have an O-ring going south. Hope it's the cap. Good luck. Jack

turbox2

Yeah, i've already tried all those diagnosis techniques. I tried a new AST cap. I filled the hose from the AST to the overflow with water and it didn't leak back into the overflow. I have a PFC commander and the temp never budges above 87 C. I've lowered the level in the overflow. I've also burped the system from the throttle body. Like I said, the car has no trouble starting, zero white smoke, full compression on all chambers, no hydrocarbons in the coolant, no bubbles in the coolant at the filler neck at operating temp, no overheating, and no water on the plugs. I can't figure this problem out. How does the hose sit after entering the overflow. Might it not be submerged in the coolant in the overflow tank?

Mahjik

iTrader: (1)

Just curious, are you filling it up again after coolant spills out? Is the coolant actually low after that?

If you are overfilling the reservoir, the pressure will kick out the excess coolant on shut down.

turbox2

Yeah, after the car is shut off, coolant vents out the overflow. Once the car has cooled off, I open the filler neck and the coolant level is down around the coolant level sensor. So, I fill it up at the filler neck to the top. I'm not filling it up through the overflow.

FDjunkie

My recommendation is that you begin pulling/replacing the radiator hoses and consider removing the radiator for the purpose of have it checked, cleaned, or even replaced.

Why? You've checked all the normal causes, its time to consider the unusual.

It seems possible to experience higher than normal cooling system pressure because of some type of flow blockage. In other words, you might be seeing a combined pressure from a normal temperature-caused increase plus an additional pressure buildup generated by the pump trying to move that water through the system. Remember you're seeing this higher pressure at the radiator caps and they are on the discharge side of the water pump. What's happening on the intake side? With a blocked discharge, the pump intake (and meaning everything past a blockage) might well be at or even below normal pressure.

So where might such a blockage occur? Since the engine block has so many passages, it seems to me that it would be very difficult to block enough of these to cause a significant pressure increase. Similarly, the radiator has many parallel passageways and there's not much to break loose inside a radiator, but the tubes could be blocked by build-up or collapsed from debris strikes. What about the radiator hoses?

Radiator hoses are normally made of two layers surrounding an internal reinforcing web. Age, temperature, and vibration can result in the inside layer of rubber separating, and if enough comes loose and/or moves, it can reduce or even totally block the flow of water. Image it acting like a sail catching the flowing water. Also, pieces (some like small sheets?) of the rubber can break free and be carried downstream to block other passages. The outer rubber layer can still hold pressure and so that no external leak is detected.

This may seem far-fetched, but I have seen old hoses that were failing in this way.

RonKMiller

A more likely scenario is that the radiator is jammed with plant parts/dust/insects/road grit/debris. How old is it? Probably 95% of the radiators tossed are thought to be internally blocked when the were blocked from the outside. Radiators have a life span, just like many other parts.

I have seen MANY radiators with minor fin damage (big deal) that were absolutely jammed with this crap. It is literally baked in there. You will only get a very small amount out by spraying it with a hose or pressure washer, and then you usually end up damaging the fins really bad. It's impossible to clean and impossible to see unless you remove the radiator and put it in front of a REALLY bright light. If this is the scenario - and I can guarantee you that it is the source of overheating problems on almost every 3rd gen - pop in a new radiator. Don't waste your money on an aluminum unit unless you are putting out huge horsepower - they are grossly overpriced and not nearly as efficient as copper/brass. Yeah, they're pretty, but so what?

Internal blockages just don't happen on ANY vehicle if the fluid has been changed every few years.

turbox2

So, is there any way to see what kind of pressure the system has on the return end, or do I just have to start replacing parts? Btw, I have a Fluidyne that is about 1 year old...

RonKMiller

Well, that eliminates the radiator. Hmmmmm...... How about doing a system flush/refill and catch the old coolant in a tub and examining it, that will give you an idea if there is any debris in the system. I doubt it, but what the heck.

This is really curious. I'm sure you already checked for kinked/pinched hoses....

turbox2

Yeah, that's the only thing I can think of (kinked hose). There's a little kink at the AST nipple cuz my M2 IC sits right up against the AST, so I guess that's next on my list of things to rule out. Almost out of ideas...

artowar2

Based on the symptoms you've reported (coolant moving to the overflow tank, but not moving back, and there is no evidence of hydrocarbons in the coolant), I suggest replacing the pressure cap and the hose between the AST and coolant overflow tank. A bad return valve in the cap, or a pinhole leak in that hose will produce the symptoms that you described.

Why do I suggest replace instead of inspect? First, for the hose, in order to get to it to inspect it, you have to remove it anyway, so don't waste your time testing it and replace it with a new hose for a few bucks. [Also, the hose tends to get plugged up with that gummy crap that ends up in your overflow tank (the stuff on the stick), though that would not relate to the symptoms you described unless the gunk was acting as a check valve...] Second, for the cap, if it's a 10 year old cap, the rubber and springs are probably a bit aged, and could stand to be replaced, again for a few bucks.