1992 Audi 100 Overheating

1992 AUDI 100
225,000 MILES • 6 CYL • FWD • MANUAL
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STEVE RUMLEY
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This car overheated while driving on higher speed country road on a moderately warm afternoon. (Coolant overflowing the little tank on the side.) The engine began to lose power at the same time. Once it cooled down, it was fine but then overheated after ten more minutes of driving. Once into town, driving slower, it never overheated.

I put in a new water pump over a year ago and the car has been trouble free and great on long trips. Here's something I'm wondering about. It has a separate exhaust for each bank and one of the catalytic converters makes a LOT of noise, as though things are loose inside. Can this cause the engine to overheat by backing up exhaust under high rpm? If not can you suggest how to trouble shoot my overheating problem?

Thanks a bunch!
Steve
Jul 9, 2010 at 8:24 AM
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INTERNETMECHANIC
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Hi, thanks for the donation. What about the thermostat? Is the cooling fan/s running? If your dual exhaust, can you feel exhaust flow on both sides, about the same? Can you check exhaust backpressure? Any applicable trouble codes?
Jul 9, 2010 at 4:13 PM
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STEVE RUMLEY
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I haven't checked the thermostat yet but the hoses feel appropriately hot. Don't know if fans should come on when driving at high speed but will check those too. I did feel the exhaust but couldn't tell if they are still separate at the end of the car or if the muffler has two pipes out of one collector. I checked the end of the muffler only at idle and each pipe feels about the same. Should check at high rpm next, I think.
Jul 9, 2010 at 4:29 PM
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INTERNETMECHANIC
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I also thought about a compression test? I normally use MOD database for specs, but, they seem to be having technical issues, I can't access.
Jul 9, 2010 at 6:39 PM
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STEVE RUMLEY
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I guess I'd just like to get an answer regarding the original post: Is it possible that back pressure or a clog in the exhaust system can cause the engine to overheat?

I need to replace the cat. converter anyway. It's all black and sounds awful...
Jul 10, 2010 at 8:07 AM
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INTERNETMECHANIC
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If it needs to be replaced, go ahead. I don't think it will fix the overheating problem, just my opinion.
Jul 10, 2010 at 10:02 AM