When to change rubber hoses?

i can't recall ever reading about a hose change or failure, but it must happen occasionally

 

I guess it depends on whether you mix and match coolants. It might be a factor in some cases, or it might not. It would depend on the interaction of the different formulations and also whether the fluid became acidic before being changed.

 

I changed the radiator hoses and other "easy to get to" hoses when I was replacing the radiator and condenser a couple years ago. I was thinking about the heater hoses, but didn't have time to pull the inverter.

That said, Honda and Toyota generally have the "best" hoses that I have seen. I will inspect hoses for damage or wear every year or two. Nasty coolant leads to electro-chemical breakdown of the rubber, which shows as a "crunchy" feeling near the hose clamps (the inner rubber layers split and eventually rupture).

IF: there's no oil contamination, the rubber is pliable (but not spongy), the coolant condition is "good" and no seeps past the hose clamps, then I leave them alone.

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Japanese chemical engineering is superior, this applies to belts hoses weatherstripping. You can usually assess the condition of a hose by squeezing it. If it's soft or hard or spongy or if you can feel a cracking feeling it's going bad. The cracking is when the nylon string reinforcement layer is actually breaking when you squeeze it.

 

The mechanical water pump will start leaking at the weep hole, start squeaking, or engine temperature may run warmer than usual. They usually don't outright die all of a sudden; though I've seen a couple of vanes or shafts break. Usually due to over-tightened drive belts.

Back in the 50's was there a coolant change interval? You were lucky to get them to 100K miles before a major break down; but labor and parts was cheap and you can actually fix things - NOT replace entire components.
The compounds used today are much better than the 50's; as long as your testing and changing your coolant as recommended - you shouldn't have to change those hoses. Do a litmus and glycol test if you need reassurance.

 

I personally would hook up a P10 HUD, so you don't have to rely on the dummy lamp that you might miss. The P10 has audio trip point alarms that you can set.