coolant line broke, is it necessary, need some help asap.

[chlubb]

There is a 1/4" hose coming from the drivers side of the coolant expansion tank that goes to a small nipple connection on the drivers side top of the radiator. For some reason, the nipple cracked and then broke off and i lost all the coolant. I have tried to JBweld the nipple back on and it worked momentarilly however it began to leak again.
THis seems to be an overflow return line although I cant find any diagram for it.
I clamped the line and drove it for quite a while yesterday with no ill effects.

Can anyone verify that this is a non essential line? My next step is to determine if I can find a plumbing fitting, threaded on one end, with a nipple on the other to JBweld into place as a permanent replacement, there is no way I am going to get a new radiator for this.

Any thoughts would be great.
Thanks,
Chris
2000 ML320

[hahnvroom]

If it was my ML i would get a new expansion tank. If you overheat your ML get ready to spend some big bucks. the tanks are pretty inexpensive.

[MB-Dude]

Originally Posted by chlubb

Can anyone verify that this is a non essential line?

To ask if the line is non-essential is sort of silly. Mercedes would not have put it in unless it had a purpose. But I think your question is really "What effect would clamping the coolant expansion line have on the engine?"

First, you must provide some sort of pressure relief of the coolant. Engine coolant systems for decades have been designed to relieve pressure through the radiator cap, channeling the 'relieved' coolant into an expansion tank. As the engine cools, the coolant is drawn back into the engine. Thermodynamics does the work and is not the purpose of this discussion.

So if you clamp the expansion line, you run the risk of over-pressurizing the coolant system – pressurized coolant must go somewhere. Something has to give under pressure and if it is not your clamped expansion line, then it will probably be a hose, or worse yet, an expansion plug. Either of these can, in the end, be more expensive than a radiator; depending on the damage.

If you drive without an expansion tank, you will eventually run low of coolant - as in the old days, before expansion tanks. I sort read in your post that this has happened.

I am only a recent owner of an ML, so am not that familiar with the W163 radiator system. I do recall that at some point Mercedes was making radiators with the expansion nipple removable/replaceable. Not sure if they still are on the newer models.

If it were my vehicle, I would fix it properly. If that meant replacing the radiator, then I would 'bite the bullet' and do it. If it's the little expansion tank that's broken, they are fairly inexpensive. But driving any appreciable distance without an expansion tank is really not good.

[chlubb]

i realized my post was misworded after your comment and yes thats what i meant. i was writing this while stuck in a parking lot trying to get a quick fix to get home and do a repair, so i was a little distraught not having a parts guide to determine what the hose was responsible for. i ended up clamping it for 5 min driving time and it worked fine.
btw, the expansion tank is fine, it was just this little nipple that mysteriously broke off.