Mechanics

COOLANT SYSTEM OVER PRESSURIZING

2001 Mazda Demio • 128,000 miles

Had a head gasket failure, have replaced it along with thermostat and all relevant gaskets, the car runs as good as ever but there is still pressure building up in the coolant system enough to push it out the coolant bottle. There is no steam exiting the exhaust and no visible signs of an external leak, when started the top hose seems to build pressure but once the thermostat opens the hose goes back to a normal state, although if I put my hand to the top hose I can feel air passing through it which also shows in the ccolant bottle, as said the car runs great without missing or running eratically as I would expect with a gasket failure again or a cracked head, no hoses are split, the radiator which was the cause of the last failure was replaced so this is good.
i am hoping that you may be able to help me out as its really becoming a nuisance now.
oh its a 1.3 16 valve b3 engine I believe
thank you
Avatar
Brucielee
October 7, 2012.



Did you have the head checked for warpage and possible cracks?

Roy

If the repair was recent, there could still be air trapped in system and this can result in high pressure than normal. When engine is cold, remove radiator cap and check the coolant level in it. Top up if necessary.

Next to check would be the radiator cap. A bad cap would not be able to hold the pressure and allow coolant to be pushed to the reservoir.

If above 2 are found to be good, I am afraid you could still be having a problem with the head gaskets. Pressure is escaping from cylinders into the coolig system and it could also be due to a bad cylinder head or the block surface is not level.

If the upper radiator hose is too soft, you would need to replace it. This can be due to the quality or age/condition of the hose.

Do you still have coolant losses and overheating issues, which yuou have not mentioned?

KHLow2008
Oct 7, 2012.
Thanks guys for the replies, ok to AESMASTER, I had the head pressure tested and also tested for level both where good, to KHLow
all hoses are good but if I put my hand on the top hose I can feel the bubbling inside the hose go past my hand, as for the radiator the hose from the coolant bottle attaches to where the radiator cap is placed so the radiator cap needs to allow coolant to bypass it into the system, if I can do it would I be able to take a video of it and put it on youtube and attach the url to a rep

Tiny
Brucielee
Oct 7, 2012.
Sorry, put it on youtube and attach the url to a reply so you can see whats happening as its hard to explain without seeing it,
thanks again

Tiny
Brucielee
Oct 7, 2012.