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| Joined: | 03-12-2005 |
| Location: | Kingman, Arizona USA |
| Posts: | 532 |
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You can find many difficult leaks by taking some white flour, mixing it with water, and making a thin dough that is applied over the suspect area. (Mud also works, after a fashion, but I don't recommend it as it doesn't discolor the way dough does.)
Okay, now that you've stopped laughing, I am serious here. Leaking exhaust tends to burn through the dough, or discolor it more at the leak than the surrounding area. IIRC somebody sells a high-tech compound for the purpose, but I'd rather spend 25 cents than 25 bucks to get the same results. Also, if perchance the dough doesn't wash off with water when you're done, it will certainly biodegrade (AKA 'rot') fairly quickly.
If you don't like the idea of using dough, you can try dishwashing liquid that's been mixed with a small amount of water, and look for bubbles. There are two problems with this method. First, the fluid tends to evaporate quickly and if you don't spot a bubble as it's being made, there's a fair to good chance you'll miss it entirely. Second, if the fluid boils, the resulting bubbles are a false positive.
Headers frequently will leak at the manifold-to-engine joint. Once an exhaust gasket starts leaking, exhaust gas tends to burn away the gasket material, so tightening the bolts rarely helps. It's important to ensure that the mating surfaces of all the header flanges lie on the same plane -- I've seen name-brand headers for V8s with more than 1/8" of difference between the front and rear flanges. (As a rule of thumb, the allowable mis-alignment is no more than half the thickness of the flange gasket.)
Possibly there's a cracked weld in the header or elsewhere in your system. Here, the weld may leak all the time, only when things are cold, or only when they are hot. Bent pipes tend to twist as they heat up, and the resultant stress can pull apart a crack that's almost gas-tight at room temperature, or force a leaking crack to seal. I've seen both.
Assuming you do have a small leak somewhere, a bit of welding may fix the problem. If this isn't possible, you might try one of those muffler sealing compounds, backed up by a thin metal sheet and a hose clamp. (Yes, this is a variant on the old beer can and baling wire fix. It's inexpensive, and it works.) With luck, this can buy you months or even years before things get too bad to live with.
And finally, should an obverver ask annoying questions, give them a ridiculous answer, such as "Bread dough? Hardly! It's British tube plaster. It was developed during World War II and was a bigger secret back then than radar. According to my research this is the proper seal for the frammis joints." :^}