I just replaced the coolant expansion tank and overflow hose in my 1989 300E. When I removed the right front wheel and well cover to thread the new overflow hose through, I realized there was no overflow tank installed. Only the mounting brackets were there.

I am planning to get a tank and install it. However, my service manual CD isn't real clear. It shows a "vacuum reservoir" and the overflow tank.

1- Are there any potential problems related to not having the tank installed, other than venting overflow antifreeze into my wheel well?

2- What function does the vacuum reservoir serve? It isn't even mentioned in the 124 Cooling System Circuit diagram.

If anyone has a digital photo of the installed assembly they could email me, I would appreciate it.

Thanks for your help.

Brother of The Benz, EstebanSPI
Not having viewed every 300E, your situation sounds quite bazar.
First thing about the function of the vac resevior. I supplies vacuum for all of the items that function on vacuum when your engine, at that moment, is not providing adequate manifold vac remain in the positionuum. This would be when the engine is under a load or when you are driving at high elevation. It also allows those vacuum elements to operate smoothly and remain in the position directed by a controller (autmatic climate control).
Second and I have no answer except if you aren't the original owner, it could have had damage at the left front fender area.
I would suggest you try to find a used overflow tank. It doesn't have to be a M/B unit just one that would fit with little mods.(cheaper Too!)
Happy Trails Beep Beep from The Spiderman in Houston!!!