Strong vibrating over 60mph. 98 ML320

Question

1998 Merc-Benz ML320

Some Back Story

Had problems sense I got his thing. It had a slight radiator leak to start with that I was made aware of at purchase. Until now, that's all it was. Since purchase (within last month), I've replaced the MAF sensor, then had to replace o-ring thing under power-steering, finally, it suddenly lost oil, so I gave it an oil change last Sunday. Then yesterday, I got up and went to go to work, and it told me I had too much oil for a few mins. So turned around to go home and let some oil out. Problem solved. Then I tried to leave again, and it started over heating. I threw in more water and tried again, but this time I noticed it leaking like crazy.

At that point I was at some gas station, not far from home, but to scared to go anywhere else. The gas station claimed no hose and only had pure anti-freeze. I didn't know what to do so I bought the anti-freeze and put some in. I made my way home and then spent the rest of the day flushing, adding, and checking the coolant and test driving it. Finally, by about 6PM, all seemed fine.

Today

I make sure the water is full and fill 2 jugs and head to work (roughly a 30+min drive on the interstate). All seems great! Till I stop at work. Immediately, only after I parked, it starts smoking/steaming real bad at the front, driver side. I look under, radiator fluid steady dripping. I pop the hood and notice fluid all over the motor, even up to the top of the firewall (i think that's the proper term). I let it sit while I worked; about 8 hours or so. I went to leave and filled it with water. After almost completely using the second jug, it seams to settle at "Cold Full". I crank it up and hit the Interstate!

FYI: I have purchased a new radiator but it won't be here for a week and this is my only means of transportation. Wish I could afford a rental, but I can't even afford this issue!

Leaving work, up until 60, everything was smooth as could be. As soon as I hit 61mph, it started vibrating bad. The faster I went, the worse it vibrated. I made it to the closest exit, about 10 miles from my work. Pulled into a truck stop, which I knew would have water. Refilled it till it settled and refilled my jugs of safety. I cautiously hit the interstate again and was pulled over for only going 60. So I tried again 70. The vibrating was not as heavy this time, but still persistent for anything over 60.

Question

I guess my question is, if I baby it and continue to fill it with water, will it make it till I replace the radiator, or is this vibrating a sign of something much worse? Any tips on what I might can do to make things better? FYI: there's no way for me to avoid the Interstate for travel to and from work (approximately 30 mins one way).

What I've Also Checked

I've also checked the motor mounts; fine. I checked for foam or discoloration in the radiator fluid and found nothing out of the ordinary. I've checked all other fluids and they are all looking good and holding fine.

UPDATE

Test today proved, it burns out the water faster, but the vibrations settle, almost to a stop at about 78mph. At 81 (i dared not go faster), it drives like it does at 50, no problems at all!

Answer 1

Is the radiator overflow tank properly connected and sealed?
Overheating can be caused by the low coolant, caused by the radiator leak. Expanding coolant would expand out the hole in the radiator making the problem worse. Repairing or replacing the radiator would fix that. Overheating can also be caused by a blockage in the coolant passages, which would cause a lot of extra pressure (coolant expansion as it heats and pressure from the water pump). That extra pressure could be overloading the radiator cap, which would throw coolant all over the engine compartment. Backflushing the cooling system should dislodge any physical blockage (kits available at most parts stores). The blockage could also be a stuck thermostat.

Have you checked everything without driving? Pop the hood, fill the radiator, run at idle until it reaches operating temp, look for signs of coolant leaks. If it will overheat at idle, watch for leaks as it overheats; if it doesn't overheat at idle then run it at 2500 rpm for a few minutes until it does overheat and check for leaks. You might see the coolant bubbling around the radiator cap, around the radiator hoses, etc. It might just be the radiator drain plug (I think that's on the driver side, bottom of the radiator). Do these checks without driving so you don't get confused with coolant spraying around the engine bay due to road speeds.

I'd gamble that the vibration is a completely different problem. It could be wheel balance, u-joints, suspension mounts, etc.