Hello all-newbie here. I just purchased a 1994 Audi 100s wagon; it has 88K miles. two things I've noticed that I wanted to ask questions about:

After I start the car, when idling and sometimes going down the road, I hear this scraping/grinding sound that sounds as if it's coming from underneath the vehicle. The exhaust system is a little louder than I expected, so I'm wonderinf if perhaps one of the exhaust pipes has loosened and is intermittenly scraping against the undercarriage? Has anyone experienced anything similar?

the other issue is coolant loss. I've had to fill the coolant tank about every 50-100 miles, as the alarm in the center of the dash will sound. I cannot find any evidence of coolant leaking anywhere--there's no water under the hood, no hissing sound, no antifreeze smell. the temperature has not gotten above just over the center mark, and it rises and falls with my speed. Any ideas? I've checked the oil, and have not seen any evidence of coolant mixing with the oil.

Thanks in advance for any advice.

 

the exaust is a possibillity .... check passanger side front floor mats and carpet if it's wet (heater core) ...

 

I checked the floor on both sides, no moisture there. It's really a peculiar thing:

I will fill the expansion tank with a coolant/water mixture before leaving for work, drive, and after about 5-7 miles on the interstate the low coolant warning light will start flashing. Today I noticed that the coolant temp. gauge rises up to just right of center, and then the alarm sounds, and almost immediately the coolant temp will start to drop. When I got to work today I immediately popped the hood, and there was moisture on and around the expansion tank, as well as the insulation attached to the hood, where it would sit directly over this area. i'm starting to suspect that the expansion tank itself is the culprit, and I have not seen/heard any steam or coolant escaping from the hoses or the engine.

Thanks for the suggestions; greatly appreciated.

 

you might be having a case of a bad coolant cap ... those thing are suppossed to hold some pressure don't remmember how much though ... audi uses a pressurized cooling system so the coolant can get hotter without boiling and if the coolant cap is not holding pressure the coolant is going to expand when it gets warmer and escape

 

or as you said expansion tank

 

When we bought our 1994 audi 100S it was making this same "scraping sound" with a very loud exhaust. When we took it in the Audi mechanic said that instead of replacing the 2 catalytic converters ($1500 a pop) the previous owner just saudered the pipes together, which causes the noise. Its a little annoying but he said it won't cause any problems.