The broken 1/4 inch air bleed nipple.
I had a small leak from the radiator but could not find where. Finally I removed the air box, which fits precisely in a very tight spot with 6 vacuum hoses hooked up to it. It was a pain to figure out where everything goes and how they fit together. But after the first time it should be easy.
Found out the tiny 1/4 inch plastic air bleed nipple, molded as part of the ABS plastic top of the radiator, had broken clear off, bleeding out coolant. I never pulled too hard on the bleed hose, but after hundred thousands of hot and cold cycles, that joint cracked and finally broke. I could see the old crack lines which may have started years ago. But it never leaked until now.
Lucky I caught it, or it could be very damaging if broken out at high speed. It was a very stupid design not to reinforce that joint.
BMW and MBZ use the same close radiators, so they have the same nipple. Apparently a lot do break. Autozone has no repair kit. Ebay has lots of folks selling the repair nipples, made of plastic or brass, between $10 to $15.
The plastic nipple looks like a push-in with self-sealing rubber seal. It looks very loose and weak. I dont see how it can seal under pressure and high temp.
The brass nipple has threads that you are supposed to drill out a bigger hole, then smear the threads with JB Weld and screw it in, making its own threads, which probably works OK for older copper/brass or even aluminum radiators, but if used on plastic it will probably leak soon, because at high temperature plastic expands at much higher rate than brass and will stretch the JB weld joint.
So I went to the Ace hardware store nearby. They have a large inventory of screws, nuts, bolts ect... Aluminum, brass, steel and stainless-steel, in both English and Metric. The showed me 1/4 inch nipples in both brass and plastic. I bought a plastic repair nipple for $1.60, made of a very hard, clear plastic, very hard, like ABS.
Used a sharp drill bit, gouging the hole bigger by hand while trying to remove the plastic debris out of the radiator. Quicker to use a power drill, but some of the debris will fall inside. For a tight fit, I coated one end of the nipple with 2-part epoxy then hammered it in the hole. It fits great.
I coated a Teflon tape in epoxy and wrapped it around the base of the joint to make sure the joint is strong and seal properly. When cured in 24 hours, the epoxy is supposed to be harder and stronger than most thermo plastics. I gave it 2 days to cure to make sure.
The nipple works great. I put the airbox back ( dont forget all those loose hoses and connectors), drain the radiator of any possible plastic debris, filled the engine with coolant and burp air out of the radiator. I checked all hoses and the entire radiator many times with a very bright LED spot light. The video camera on flexible fiber can also reach into inaccessible crevices.
There wer no leaks. The radiator draining and burping procedure works logically and perfectly the first time, taking only about 2 hours. When you understand how the system is designed to work, and find it working logically, then you feel assured and have confidence in the system.
Anyway I think my plastic nipple glued in with epoxy is plenty strong. I would check for leaks from that area frequently every time I open the hood just to make sure it does not leak. If it does leak, I can remove the airbox fairly quickly and make the repair.
Since there are a lot of repair nipples on sale in eBay, looks like BMWs and MBZs also have a lot of broken nipples. I urge the bros to take the time to take out the airbox and inspect/repair this nipple to prevent leaks and engine damages.
Toyota dealer wants $400 for a new radiator. I told the guy I can buy after market radiator for about $100. He said the aftermarket radiator may only last 1 year then have to be replaced. I dont believe him. I no longer trust their flimsy plastic-top radiator. I used after-market radiators on other cars and they worked reliably for years.
Apparently Toyota uses KOYORAD radiator as original equipment. You can find KOYORAD all-aluminum radiator in eBay for $95. Make them sign a lifetime warranty and hold them liable if it leaks.