Gumout fuel injector cleaner for high mileage cars...

I usually use a fuel injector cleaner every couple of months, but I hadn't used one for a while. I'd been noticing that my fuel economy was about 25-26mpg at a steady 80mph (which seems low.) So I decided to add the Gumout this time (as I had it sitting around).

My car now has about 140k miles on it so you would assume the engine is starting to get tired... after filling up with a fresh tank of premium with the Gumout, I immediately noticed an increase in power and smoothness! The engine felt so much "looser", it felt like as if all the horse power was free (I have an EAT chip, a K&N air filter, and use synthetic oil). Needless to say when I took it on the highway I was now getting 30-31mpg at a steady 80mph!

I guess it just goes to show that you need to clean your engine internals to get the best from these engines, but to get a 4mpg increase is very cool. My OBC was showing a range of over 500 miles, which I hadn't seen for a while.

I've now decided to add fuel injector cleaner every other fill-up, as the mileage increase is worth the extra expense.

30 mpg on a flat surface @ 80 is a bit freakish in terms of fuel economy!

Is your mpg real numbers? or from the computer?

I find those mileage figures a little difficult to swallow.

It's a M50TU engine with an EAT chip connected to a slushbox. The gas mileage is off the OBC - so it's possibly not a perfect assessment of real gas mileage.

But that said, my OBC was saying 26mpg before the Gumout, and then 30mpg after, so it at least it was consistent. If my real gas mileage is only 28mpg, i'd still be impressed... it showed improvement and the engine feels looser and livelier.

Do a test... fill up car... reset trip meter and drive until you refill... then calculate your actual mileage.

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Originally Posted by Tiger

Do a test... fill up car... reset trip meter and drive until you refill... then calculate your actual mileage.

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I'm usually in a lot of stop and go traffic, so my average mileage is closer to 20 to 21mpg. So a test for actual gas mileage will probably have those results (give or take 1 to 2 mpg).

That said, I'm just happy to see my highway mileage go up, even if it's only on the OBC (my assumption is that my average mpg will also go up slightly). Even if the new mpg numbers are bogus, the fact that they changed for the positive means that at least the OBC thinks that the gas mileage has increased.

The perfect test would be to get on a highway with a full tank and then measure how far you can go before you run out of gas. That would give you a true range and mpg (for highway driving).

i've tried an injector cleaner before but didn't see such dramatic results - I will try the gumout one on your reccomendation.

I get similar mileage on my 95 with the EAT chip.

Some say injector cleaners should only be used once per oil change? Something to do with oil contamination or dilution. Others may know for sure.

fuel injector cleaners generally contain things like alcohols, napatha, things generally used in emissions passing chemicals, et cetera, that will raise fuel economy for the time that any significant portion remains in the tank. maybe it will go down 2 or so.

also...if you are about to need an oil change, those chemicals generally DO dilute your oil, so it may have knocked the hot grade of your oil down 10 or so, which would increase your fuel economy. this is providing that your oil was tired, though.