I was hunting down a problem with the AFS (blinking light) when I noticed that a splotch of greenish residue on the engine cover around the oil dipstick. I checked the reserve tank - bone dry. Refill radiator and reserve tank - about half a gallon needed. Problem turned out to be a bad radiator cap. Dodged the bullet here - car did not overheat. Cost to me was one new $15 radiator cap. Never had one fail on me before, the plastic valve at the end decided that it didn't want to be part of a radiator cap anymore and liberated itself. It is now living a simple life somewhere towards the passenger side at the top of my radiator. It can't possibly get down into the fins and the flow of coolant should keep it from getting back to the fill end. I am thinking that I will be ok on this...

Keep an eye out for green residue.

Good vs bad one!

 

I never knew radiator caps went bad until we learned the hard way in my then GF's 1994 3.slow 4Runner. She had just had the power steering pump, water pump, and radiator hoses replaced within the month that we tried to take a trip to the beach. After multiple overheats and coolant refills (stupid on my part to try and continue), one of the cylinders cracked. Turns out the $7, 15 year old radiator cap was bad and the shop didn't bother to replace it.

Since then, I have read that, to be safe, you should change your cap every 7 years. Most will likely scoff at the idea, but if $1/year is the worst to happen to you, I would call it a win.

 

Hmm. I didn't know this. All of my cars are old. Maybe I should just get new caps in them all.