Radiator neck broke

Replace the radiator... don't gamble on that neck... it will crack again. The tranny cooling line is easy and simple...very little oil will drain out.

For now. Many people have tried to repair this to no avail. The price for failure here is high. One guy did clean it scrupulously, apply JB weld then wrapped the whole neck in thin metal and that's worked.

But most people replace the rad. They're not too bad mail-order.

I've never had a 300E but in 108's/126's there's an oil cooler on the side of the rad. It's a separate unit and have never heard of one failing.

Guenter,

If I were going to attempt a repair, I think I would find a metal sleeve that I could insert into the existing neck segment, then I would use a silicone rubber adhesive to seal it neck back together again, with the piece that broke off.

You may also put a sleeve on the outside of the repair to give added strength.

Replacement may be a better option. But if I understand the cause of these failures often it is the type of anti-freeze that causes the plastic to become brittle.

If your car is equipped with an oxygen sensor be sure to select a grade of silicone that is listed as safe for these as it is my understanding that it does not take much vapor from the curing rubber to kill off the ox sensor.

Plastic is impervious to alot of things.. what cause the breakage most of the time is the expansion and contraction of plastic to the point it become brittle.

Other reason for breaking is the radiator hose clamp is tightened too much that it will hasten the process.

Another common cause for the breakage of the plastic radiator neck is transmitted engine vibration due to worn or failed pneumatic motor mounts.

Randy Steele used to posit that it was the vibration combined with heat that did them in.

I own an '89 300E, my radiator broke the same way. Unless you can create another lip on the break area, replacement is best. I replaced mine in about 15 minutes. It cost 135 bucks online for a new radiator.