Rusting radiator cap…

[J]

I recently noticed on this 2001 Altima that the radiator cap is rusting. I’m planning on changing the cap, hoses and coolant soon. The hoses aren’t related, some are oil soaked and some are starting to tear because a mechanic over-tightened the clamps.

I already have the new hoses and cap. What I’m worried about is the new cap rusting as well so I’m trying to figure out why it would rust and it would be cool if anyone had any ideas.

This car has been in front-end collisions more than once so the mechanic had to replace the radiator and I think he just carried the old cap over. Or it could be a cheaper cap that came with the radiator. I’m torn on whether it’s because the cap is old, the cap is cheap and made of inferior metals or the coolant is inferior. This car is using bright green coolant. I don’t know what brand or type he put in here but I think it’s safe to say it isn’t Dexcool. What I’m noticing is that when I pull the cap the whole underside is rusting. This is what the cap looks like:

The spring, the shaft inside of the spring and that metal disc up top are rusting badly. The filler neck has a ring of rust where the coolant would push the center up to get to the overflow reservoir. The overflow reservoir itself is loaded with dark brown coolant with rust bits deposited on the walls of the reservoir. The coolant inside of the filler neck appears green, I can see some rust deposits below the surface though. I suspect the rust is mostly confined to the filler neck so when the coolant overflows to the reservoir it pushes the rust from the cap into the reservoir but not necessarily pulling rust back in when it draws back in. I won’t know for certain until I drain the system for color.

I’m planning on using what I believe is decent coolant, the Peak universal long-life stuff that’s greenish-amber in color.

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[college man]

It could be a cheap cap. To develop rust either the coolant has not been maintained with the proper
50/50 mix You may want to flush any rust out of the system change the thermostat and hoses. Refill
with new green coolant and replace the cap. I have had good luck with stant brand.

[Author]

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