Yesterday, coming home I noticed my temp was a few degrees higher. Got up to 87*C when it is normally 82*C with almost no fluctuations. I have an aftermarket electric Blitz temp gauge installed in the stock water temp sensor's position.

At times temp would get up to 87* and at other times would hang around 82*C and a few times dropped slightly before 80*C.

When I got home I let the car cool down and after the coolant system depressurized I noticed the upper radiator hose had slightly collapsed. I took off the pressure cap and the hose went back to its normal shape because the suction was released.

The radiator cap and T-stat are new and OEM with a few thousand miles on them. I figured it was a faulty radiator cap and replaced it but again tonight the temp was slightly higher and the hose had collapsed again after cool down.

What would cause this?

I have an OEM tstat to swap in if that may be the problem, but that does not explain why the when the pressure cap is removed the suction is released right?

 

I've had this sort of issue before... You might want to check and make sure fluid can flow freely through the hose to your coolant overflow tank. If that hose is blocked, it could give you that suction in the cooling system.

 

my car has been doing that for 2 years, if it is a problem let me know,
Wont releasing the suction introduce air into the system?

 

no...as the rad cools down, it should just draw coolant back from the expansion tank.

 

exactly, and if there's enough suction to squish one of your radiator hoses, it's a sign that the system is not able to pull the extra coolant it needs from the overflow tank. It just puts un-needed stress on the radiator hoses, forcing them to squish and expand every time the car heats up and cools down. It's not really an immediate problem, but it's like when you take a peice of plastic, and bend it over and over again at the same place... eventually it stretches, weakens, and then finally breaks.

Oh, and as for the fluctuating temperature, that may have something to do with the fact that your cooling system can no longer regulate the pressure of the coolant, and the pressure difference can cause differences in how well the coolant cools.

 

Unless the vac line going to the expansion tank is clogged (cold winters + short drives would do this)... In which case the engine won't be able to pull from teh expansion tank, annnd... you'ld probably get the add coolant light (even though you look and see fluid in the tank)

 

Thanks guys for the quick replies. I will check to see if the path to the overflow is clear. So there is a very unlikely chance it is due to the tstat correct?

Just wanted to add all coolant hoses are brand new as well as all other items associated with the cooling system. Radiator hoses are still very soft and pliable.

 

The radiator cap is not opening to allow coolant back into the system. Go buy a new one from Mazda.

 

^ NZ is that s4 specific, or S5s too? How does that work?

 

Simple solution to this is, new radiator cap, and new silicon coolant overflow hose.

Don't screw around. It is not a good thing when the hoses colapse because your expansion system isnt working correctly.

 

Expansion system

No seriously, how does the pressure cap divert the pressure/vac to the expansion tube/bottle though?

 

Its like boiling a pot of water with the lid on. Pressure builds up and pushes. Same in the coolant system. The cap is designed to open when pressure reaches .9 bar and allow fluid to go past. The only place for it to go is the over flow tank. Once it cools off, the vacuum created by the loss of fluid will suck it back in. The fluid doesn't have the same displacement when its cold. The cap itself has a rubber diaphram that is on a spring to allow it to move up and down, opening or closing the passageway.

Not having a pressure cap would cause the pressure to build up until the next weakest link in the coolant system gave out, which would probably be a coolant seal. Did I ever tell you the story about how my car didn't have a pressure cap when I bought it?

 

http://auto.howstuffworks.com/cooling-system7.htmhttp://auto.howstuffworks.com/cooling-system7.htm

 

http://auto.howstuffworks.com/cooling-system7.htm

 

ding ding ding!
we have a correct answer!

 

That would be a bit hard to believe.... seeing as the original post states "I figured it was a faulty radiator cap and replaced it"

 

I had this same problem on my VR-4 execpt it would make the upper rad hose FLAT haha. It was becuase there was NO overflow tank on it... so I put a cheap one in there....

As others have said...Its definately either the radiator cap not letting the fluid draw back into the system. Or you have a plugged up line going from the radiator cap to the overflow tank.

 

you could have your hoses mixed up on the overflow cap as well check that also.

 

It's specific to just about every car made in the last fifty years. The radiator cap has two valves in it, one to let pressurised coolant out and one to let it get sucked back in. That HowStuffWorks article should explian everything.

 

just add water. rev the motor and throw the water cap on asap

 

sometimes the hose on the top near the radiator gets a slight kink in it due to the angles involved, espeically if you have gone to an aftermarket radiator ... check to see if there is any bending occuring where the hose is collapsing, I mean bending beyond the pre-formed shape of the curve. If there is, it is making it alot easier to collapse it with vacuum than it would be otherwise.

Which brings me to my second piece of info to add here, just like the radiator cap requires a certain amount of pressure before it will open and overflow into the expansion tank, it requires a certain amount of vacuum before it will open and permit fluid be drawn from the expansion tank. The cap has a spring on each valve, the vacuum has to overcome the force of the spring before it will open the valve. So if your hose is easier to collapse than the spring is to compress, your hose is going to collapse.

Make sure the hose is not especially easy to collapse in that spot, I have had this problem on my car with the AWR radiator, since it is so thick the oem hose does not match up quite right with the angles, making it want to kink right at the top of the radiator.

The expansion facilities may be operating perfectly fine while having this collapsing hose problem. When the valve opens and teh coolant gets drawn back in, it will continue to flow until the spring can close again. This depends on the cap, how strong the spring is, but it is very possible you will have some residual vacuum even after the system has contracted fully. You may have noticed that sometimes when you open the radiator you hear air flowing, even after the engine has cooled down, it's probably air sucking in, not blowing out.

 

Seems the problem has solved itself. After I replaced the cap with a good one I forgot to put the cap on the overflow on fully and all the coolant was gone from the overflow after I changed out the hose going to it. Filled it up and seems to be fine now. Thanks guys. It was the cap.