Craked exhaust manifold consequences?

[Dave]

Hello,
I own a 03 Civic LX (1.7L) and I got a cracked exhaust manifold. I can’t see it because of the heat shield is in the way. I made the diagnostic based on the sound engine does (and it is a pretty common issue with these). At the beginning I wanted leaves it as is (I can live with a noisier engine) but I ask myself how could it affect my fuel consumption or could it harm something? Could air infiltration through the crack affect the air fuel ratio (resulting in a richer air fuel mixture)? And second question could I remove the heat shield to have a better look and try to weld it to seal the crack? In other words, will it harm something without the heat shield? Thanks in advance,

Topic

[Billy]

1. I’ve had 2 Civics with cracked exhaust manifolds. Neither of them had any noise from the crack. Certainly a severe enough crack could create noise, but are you certain it’s not just the manifold gasket?
2. If the crack (or gasket leak) is severe enough to vent, then absolutely it can throw off your O2 sensor readings, typically reading lean and causing positive fuel trims, negatively impacting fuel economy, emissions, and catalytic converter lifespan. Monitoring your fuel trims would be a great first step.
3. Replacement exhaust manifolds are cheap, starting around $100 with cat.

Running without the heat shield, to find the leak, is fine, but I wouldn’t leave the shield off forever. Keep in mind that manifold heat shield bolts tend to rust thoroughly in place. You can expect to shear as many as you remove intact, even with proper rust removal in advance. If they’re bolted straight into the manifold, rather than bolt and nut on a bracket, you won’t be reattaching the affected points without difficult extraction/repairs that will be more trouble than the manifold is worth.

[Author]

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