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1project2many · 01-03-2018, 09:53 AM

Here's the NH rule for heat shields. It used to apply to all vehicles but I only see it in the bus section now.

"The exhaust system shall not pass within 12 inches of the fuel tank and its connection, or any flexible brake system hose, unless a heat baffle is used, in which case a minimum exhaust system separation of 1.5 inches shall be maintained to the fuel tank, its fittings and any flexible brake system hoses. The exhaust system may be less than 12 inches from the fuel tank on diesel powered buses."

With exhaust under a tank, even if nothing melts, the fuel can get very warm which can cause vapor leaks and fuel odors, can cause excess vapors to be drawn into the charcoal canister, and can cause spark knock. But if you think about vehicles using plastic tanks today vs metal from the past, I think the OEM's run exhaust remarkably close to the tank.

01-03-2018, 09:53 AM	#8
1project2many Registered User Join Date: Mar 2012 Location: Lakes Region NH Posts: 3,157	Re: Exhaust under fuel tank Here's the NH rule for heat shields. It used to apply to all vehicles but I only see it in the bus section now. "The exhaust system shall not pass within 12 inches of the fuel tank and its connection, or any flexible brake system hose, unless a heat baffle is used, in which case a minimum exhaust system separation of 1.5 inches shall be maintained to the fuel tank, its fittings and any flexible brake system hoses. The exhaust system may be less than 12 inches from the fuel tank on diesel powered buses." With exhaust under a tank, even if nothing melts, the fuel can get very warm which can cause vapor leaks and fuel odors, can cause excess vapors to be drawn into the charcoal canister, and can cause spark knock. But if you think about vehicles using plastic tanks today vs metal from the past, I think the OEM's run exhaust remarkably close to the tank.