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Right after fixing another problem with one of my cars ( 98 Mazda 626 GF 2L ), I revved the engine and all of a sudden heard the tell tale hiss of a coolant leak:

enter image description here

As you can see, this hose just sprang a leak. Not a big deal, it's probably the original hose, and almost 18 years old.

However, I've had three different hoses go like this in a short period of time, just a few hundred kilometers of driving ( all on the hot side between the heater core and radiator ). Now, I've already replaced the thermostat, which was stuck shut and to which I attributed the previous two hose leaks, but this new leak has got me worried that maybe something else is causing pressure build up in the system.

There is no noticeable overheating, and I'm using a 1.1 radiator cap ( WSM calls for between 0.95 - 1.25 ).

Can I reasonably attribute this to old hoses and coincidence, or should I be looking for some other problem?

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    When one hose blows like that I always try to replace all the hoses. Too many cases of serial failures. And I would replace that worm drive clamp with spring type seen on the leaking hose.
    – Fred Wilson
    Apr 18, 2016 at 16:21

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Remember that the reliability of any system of components will only be as strong as the weakest link.

Coolant lines are pressurized under regular operation and the walls of the hoses will weaken with many, many heat cycles.

It is expected that a coolant leak will spring at the weakest point of the system. The moment you replace this hose, the weakest point will shift to some other location (likely another hose). This is why it seems like one hose fails after another.

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    Nice explanation of 'cascade failure'
    – DucatiKiller
    Apr 18, 2016 at 17:48
  • Absolutely ... I should have named "cascade failure" in mine as well ... this is a great explanation. +1
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Apr 18, 2016 at 22:20
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I believe (and this is a gut check) you can chalk this up to deteriorated hoses which all have gone bad in the same period of time (coincidence). Each has probably served a long fruitful life and now it's time for replacement. Especially considering where you live and overheating as well, this does not seem unreasonable to me.

I'd suggest if you have any other hoses which have yet to be replaced, you take care of it. I don't think there is a systemic issue which is going to cause new hoses to rupture again (considering your description). There is no way I could guarantee this behavior (obviously), but considering the history, I'd say after new hoses the vehicle should be in pretty good shape from this aspect.

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    Consider replacing vacuum lines as well as coolant hoses. They are all rubber (in most cases) and all have the same deterioration issues.
    – JPhi1618
    Apr 18, 2016 at 14:35
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    It would certainly stand to reason that all of the hoses, being the same age and subject to the same useage, would fail at around the same time.
    – Steve Matthews
    Apr 19, 2016 at 14:37
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A leaking head gasket can lead to exhaust pressurizing the cooling system. This will generally fail the current weakest link in your cooling system. As you replace one component, the next weakest component will fail.

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  • I was actually worried about that at first, but I recently checked compression on all four cylinders, and it was good and high with indication of leaks, so I figure that's not the issue in my case. Also, I would think I'd see either oil in the coolant or foaming in the oil, neither of which I've got.
    – Robert S. Barnes
    Apr 18, 2016 at 18:33
  • If the system returns to normal pressure after cooling down, this is unlikely to be the problem. A HG leak doesn't always mean you'll see oil transfer, though.
    – R.. GitHub STOP HELPING ICE
    Apr 18, 2016 at 20:57
  • That's supposed to read, "with NO indication of leaks."
    – Robert S. Barnes
    Apr 19, 2016 at 4:39
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It could be a stuck or blocked radiator cap. Did you change the cap at any stage? If the level in the coolant reservoir fails to rise and fall with engine temperature that could be a clue.

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  • I checked the radiator cap and it is working ok.
    – Robert S. Barnes
    Apr 19, 2016 at 4:37
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If the pressure relief valve was (or still is) stuck, as well as the thermostat, quite likely you have weakened all the hoses. Or, they are all dying of old age, though three in quick succession seems an unlikely coincidence. Pragmatically, after 3 failures I would replace all the hoses and clips, plus I would test the relief valve is opening at the correct pressure. If you get more failures after that, then keep looking until you find the root cause of all of them.

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