Noise from front of engine
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,498
Likes: 4
From: Brentwood TN
Noise from front of engine
I finally got a chance to get under my '98 coupe and try to resolve the thup-thup-thup noise coming from the front of the engine. It sounded exactly like a bad valve in the air conditioning compressor except I don't think this compressor works that way.
Recapping - the noise was there, A/C on or A/C off. It got louder as the engine warmed up. It increased and decreased in frequency with increase and decrease in engine speed. There was no visible run-out on the harmonic balancer.
I swapped out the A/C belt and the main accessory belt (no idea how old they, there is a chance they are OEM and the car is almost 13 years old and just under 100K miles) and the noise is gone.
Based on my experience and other threads here and other sites, a lot of mischief goes away when these belts are swapped out.
Odd note - I had a belt that I thought I had bought for my C-4 maybe 6 years ago (sold in 06) and the part number is the same as the belt for the C-5. Does anyone know if the belts are indeed the same? It seems unlikely given the very different layout on the engine, but maybe they are.
Charlie
Recapping - the noise was there, A/C on or A/C off. It got louder as the engine warmed up. It increased and decreased in frequency with increase and decrease in engine speed. There was no visible run-out on the harmonic balancer.
I swapped out the A/C belt and the main accessory belt (no idea how old they, there is a chance they are OEM and the car is almost 13 years old and just under 100K miles) and the noise is gone.
Based on my experience and other threads here and other sites, a lot of mischief goes away when these belts are swapped out.
Odd note - I had a belt that I thought I had bought for my C-4 maybe 6 years ago (sold in 06) and the part number is the same as the belt for the C-5. Does anyone know if the belts are indeed the same? It seems unlikely given the very different layout on the engine, but maybe they are.
Charlie
Tech Contributor
Joined: May 2008
Posts: 2,843
Likes: 16
From: Howell Michigan
St. Jude Donor '09-'10-'11
I swapped out the A/C belt and the main accessory belt (no idea how old they, there is a chance they are OEM and the car is almost 13 years old and just under 100K miles) and the noise is gone.
Odd note - I had a belt that I thought I had bought for my C-4 maybe 6 years ago (sold in 06) and the part number is the same as the belt for the C-5. Does anyone know if the belts are indeed the same? It seems unlikely given the very different layout on the engine, but maybe they are.
Charlie
Odd note - I had a belt that I thought I had bought for my C-4 maybe 6 years ago (sold in 06) and the part number is the same as the belt for the C-5. Does anyone know if the belts are indeed the same? It seems unlikely given the very different layout on the engine, but maybe they are.
Charlie
The noise could have been the belt part number stamped on it. There were some that the label was proud of the surface and would sometimes develop material on it with time/use. This would make the bump noise worse. If you still have the old belts that came off take a look at the label area and see if it looks raised.
Glad to hear you got it fixed!
Thread Starter
Melting Slicks
Joined: May 2000
Posts: 2,498
Likes: 4
From: Brentwood TN
I'll look the part numbers up Monday morning. What year was your C4?
The noise could have been the belt part number stamped on it. There were some that the label was proud of the surface and would sometimes develop material on it with time/use. This would make the bump noise worse. If you still have the old belts that came off take a look at the label area and see if it looks raised.
Glad to hear you got it fixed!
The noise could have been the belt part number stamped on it. There were some that the label was proud of the surface and would sometimes develop material on it with time/use. This would make the bump noise worse. If you still have the old belts that came off take a look at the label area and see if it looks raised.
Glad to hear you got it fixed!
The C-4 was a '91 A4 coupe.
Charlie
Tech Contributor
Joined: May 2008
Posts: 2,843
Likes: 16
From: Howell Michigan
St. Jude Donor '09-'10-'11
