I have a 2000 Accord EX 4 dr. sedan, 4 cyl, A/T : I have been experiencing temp. gauge fluctuations, coolant reservoir filling and bubbling, etc. I discovered that my radiator cap was broken. I was able to fish out the spring and the big plunger piece. But, a small white ( plastic ) ring that is part of that unit is missing. I must presume that it's in my radiator. Can I just leave it in the radiator or what can I do about this ? The radiator cap has been replaced and so far the car is running fine and the above-mentioned problems have disappeared. Thanks much for any input.

 

If you have no overheating problems, don't worry about it.

When the time comes to change your coolant, you may want to remove the radiator and flush it out by pouring water in it upside down.

 

I agree the cooling tubes in the radiator are too small for the anything from the cap to cause any problems.