Hey all, I'm almost afraid to ask this... '72 350. I have what sounds like an exhaust leak on the passenger side that I've been chasing for months. The weird thing is I only get it under load...only while driving it. Not idling and revving it in the driveway. Without pulling the engine, I can't find anything. Not that I can actually see the whole exhaust manifold anyway. There was a missing bolt that I replaced which didn't change the sound, so I assume it's maybe a blown out manifold gasket(s) or crack I can't see. There's no visible evidence of a leak. The scary part is why I only hear it under load? Anytime I've had an exhaust leak, I can hear it all the time. If it was a valve train issue, I would hope it would show up at high RPMs just sitting. I can't get the pass. valve cover off because of lack of room at the rear fastener, so I can't see if it's a valve train issue up top. I'm taking care of that as soon as the car is out of storage. Could a lifter or rocker sound like that only under load on the street? I drove it 3000 miles on Power Tour last year and the noise never got worse and it runs great. Every cylinder is working fine with perfect looking plugs. Thanks
Bad engine mount, causing the air cleaner housing to touch the bonnet? Open the bonnet, start the engine, put it in gear, hold the brake and hit the accelerator. If you see the engine rising and tilting, it's the motor mount.
A bad motor mount can allow the engine to rock enough to have the fan hit the shroud. Put the car in gear and apply the throttle with the brakes locked up, do you then hear the noise?
Lock the E brake, block the tires. Put it in gear get under the hood, bring up the RPMs from the carb n listen.
No...it's not that kind of sound. I suppose I could throw my GoPro under the hood and drive it to record the sound.
It’s probably the exhaust manifolds to the head. Or even the exhaust crossover . I would get it in a lift and check underneath. Check exhaust pipes check the torque converter bolts and flexplate for cracks while you’re there. You describe a clack but it may be something else
Yeah...until I can get it pulled apart I'm guessing. Praying for a cracked manifold. The fact it hasn't changed at all in 3000 miles gives me hope.
If it's an exhaust manifold and you can't see all of your manifold like you said. Try putting in engine valve cleaner additive and see if smoke comes out of a crack in the manifold or a blown manifold gasket. Vet
You can also pull plug wires one at a time and drive it. Once the noise goes away you'll know which cylinder is leaking.
My exhausted leaked a slight bit under load.... I dropped the exhaust from the manifold cleaned up the flange connection... Done...
More than likely it’s a leak from your exhaust manifold. It’s probably a tiny leak, that’s why you only hear it under load, when the exhaust gets hotter and pressure goes up. It’s a pretty common symptom on manifold leaks that are just starting.
My favorite way to test for exhaust leaks is a shop vac in reverse taped to the exhaust tip. Then you can spray the exhaust down with Windex when cold and any leaks will be really obvious. It also lets you put your hands way up in there to feel for leaks which you wouldn't want to do while hot!
