Improving performance in a 1994 GMC with Sea Foam [SOLVED]

I have a 1994 GMC c1500 with a 5.7 liter 350 vortec and it seems to get terrible gas mileage, like 9.5 on a good day. I’ve put two cans in the full 26 gallon fuel tank. Should I do this again? Also I have put Sea Foam Spray down the throttle body but it is separated into two barrels. Do I use a can in each, and do I have to change the spark plugs after?

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Jim D.
Jim D.
2 years ago

Hey Cody – good questions and sounds like you’re on the right track for recovering your GMC’s performance.

While you can add Sea Foam to the tank at any time, putting a full can or two in a low tank of fuel is the best way to clean. It’s made with 100% safe petroleum cleaning and lubricating ingredients, so it can’t harm anything and it’s completely safe to add in high concentrations. I’d put a full can of Sea Foam High Mileage in a low tank of fuel (3 gallons or so). Then, drive 10-15 miles or so before adding fresh fuel so the high concentration has a chance to work. It’s a great way to clean!

About the throttle: you can simply split the can between them. It takes about 6 minutes to empty a can of Sea Foam Spray, so 3 minutes in each should do it. You don’t have to change the spark plugs after.

Hope that helps!