I have a 90 740 gle wagon w/ 152k miles on it. there is a tinny buzz at approx 2400 rpm. I have traced it to the exhaust system where it comes off the manifold. It appears to be a 2 layer pipe of some sort. Any suggestions on how to stop it from buzzing. (and please, no comedians telling me to keep it under 2400 rpm).

Also, the radiator flange just failed, which I understand is a common failure (it is also common on BMWs which I have much more experience with). I used some abs/pvc glue to glue a piece of pvc pipe inside of what was left of the flange and glued a second piece of pvc around the first piece to bring it up to the proper outside diameter so the hose would fit properly. I reinstalled the hose all the way up on what was left of the original flange and tightened the clamp. Has anyone else tried this repair, and if so, did it hold up and did it restrict the flow of coolant too much? I just did this, and so far it seems to be ok.

Dave, I thought you HAD to be a comedian to own an older Volvo

I've tried a similar radiator fix. It was short lived. You'll be out a hell of a more than the cost of a new radiator if that thing blows and you keep driving without knowing it.

The heat shields are notorious for buzzing. Have someone run the engine, and get a stethoscope or long screwdriver and poke around and listen to locate the buzz. The heat shield in the engine compartment right off the manifold is notorious for losing bolts. Make sure they are all tight. Also, that heat shield sometimes cracks, then rattles.

Don't worry. Be happy.

It's not the heat sheild. It is cracked, but that is not the source of the buzz (I took the heat sheild off and it still buzzed). I layed down on the garage floor w/ the drivers door open. With my right hand reaching in to press the accelerator, I had a broomstick in the other hand. If I pushed the broomstick to the exhaust just below the manifold, it stopped the buzz. Now that I found it, I just need to solve it. I'm just somewhat limited because of the heat. On a positive note, I did eliminate a horrible squeek/rattle in my BMW 325 convertible. I though that the toneau cover was rattling, but a little wd40 on the rear shock mounts did the trick.

I had a plastic radiator that failed as you describle as well as on the side seam. I tried various repairs with various adhesives but it will fail again. The plastic has deteriorated and has no integrty. This is a common problem and there is no fix except replacement.

Replace with an all metal rad. I can suggest one from Nissen.

What ever is loose on the exhaust tighten it, flex it, shim, whatever, to stop the vibration. Not sure what the 2 layer pipe would be but maybe you are looking at a shield which is loose and vibrates.

What about keeping it over 2400 RPM?