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Broken Radiator Cap

I have a 2001 Toyota 4Runner with 4wd. It has been well maintained and with 168,000 miles is in excellent mechanical condition. Each year it gets a radiator flush and fill. And every two years new hoses and belts.

Recently during the annual flush and refill I noticed that the very bottom part of the radiator cap was broken off. This is a small plastic plunger and washer about 1/2" in diameter. This damage could be a year old or one day old. I fished around with a wire and mechanical grabber, but had no luck finding the piece.

Questions are: Can this piece get out of the radiator? Where can it go? Will it destroy the water pump or will the water pump eat it? Could it cause harm in the water jacket of the engine? Could it cause overheating issues?

Could someone hire you as a Professional Worrier? The coolant only needs to be replaced at three to five year intervals. Yearly is overkill.
I wouldn’t worry about that small piece; but, if you must…

I guess it is possible that the part could get somewhere that it could block something and cause overheating, or maybe even damage the water pump. However I don’t think I would get all that worried about it.

I also agree with hello about the maintenance you are doing. Back in 1965 when I bought my first car, we did coolant changes every year, but today we have far different coolants and cars. All that changing is not necessary. Check your car’s owner’s manual and with the exception of the automatic transmission fluid that should be changed about every 30 - 40,000 miles, you can safely use the numbers published in the owner’s manual.

Can this piece get out of the radiator? No.

Where can it go? Nowhere.

Will it destroy the water pump? No.

Will the water pump eat it? No; it will never get anywhere near the water pump.

Could it cause harm to the water jacket of the engine? No.

Could it cause overheating issues? No.

Now, go find something else to worry about.

There is a greater chance of damaging your radiator fishing around with the wire and the grabber than the plastic will cause. I like you would not like to have that floating around potentially causing a problem with a pump, valve or thermostat in the cooling system, but believe the fluid in the radiator goes from top to bottom so the parts are probably on the top of the radiator to big to go through tubes in the radiator. You might be able to remove the upper hose, back flush the radiator and get them out, but probably not worth the trouble. If you want to try another way draining some fluid and a small rubber hose taped onto a shopvac might work

If the plastic piece is bigger than those little slots you can see under the fill hole, it is probably somewhere in the upper part of the radiator tank. If it is light enough to float, it might be in the overflow tank or the hose leading to the overflow tank.

You could possibly get it out by draining the radiator, removing the radiator, turning it upside down and shaking it. But that would be an awful lot of work.

I suppose that there is a remote chance that the plastic piece might eventually somehow find its way to the thermostat, water pump, or heater and actually cause some trouble. But that’s pretty unlikely and probably best dealt with if/when it happens – which is most likely never.