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When gas goes bad ...

| Saturday, Aug. 3, 2013, 12:01 a.m.

Question: Around Christmas I changed jobs. My Tundra, which had been driven between 150 and 350 miles a day for 250,000 miles has been driven no more than a thousand miles since. Which leads to the question; how long can petrol (gasoline) sit in the tank before it becomes stale, rotten, yucky or whatever happens when it goes bad? And what to do about it, or better, prevent it? Additionally, is there any reason to change from 25,000 mile oil changes?

I use AMSOIL SAE 0W-30 Signature Series 100 percent Synthetic Motor Oil with the Amsoil EA oil filter, both rated for 25,000 mile/one year between changes.

Answer: Gasoline does degrade when stored, due to the effects of heat, light, air and water contamination. Our mandated E-10 and E-15 fuels, containing 10 percent to 15 percent ethanol, absorb water at a much higher rate than straight gasoline. Chevron says gas that's stored in an air-tight environment can last up to one year although there's lots of folks that claim three months is when things start to go sour. Vehicles built during the past two decades have very tight fuel systems in order to minimize hydrocarbon emissions, meaning what's in your Tundra's tank fairs a lot better than the gas in the lawnmower or a red container. Gas that darkens in color or takes on a stale odor really isn't fit for use in modern vehicles.

I store several vehicles in Alaska nine months per year, under fairly harsh conditions, and treat their fuel with STA-BIL prior to departing. I've been a little surprised to have no fuel problems at all when I return each summer. The Suburban pings a little on long grades almost the same on the old gas as it does with a fresh tank! It sounds like even with much less use, you're still refilling with fresh fuel perhaps every couple of months?

Your new driving schedule will likely be tougher on the Tundra's oil, especially if your drives are less than 10 miles in length or involve a lot of idling (Amsoil puts you into the “severe service” category here and reduces maximum miles to 15K — still one year). I'd have no problem with the one year interval and low miles, unless you detect signs of moisture condensation or sludge beneath the oil filler cap.

Q: How does coolant circulate in an engine? I recently had to have an expensive repair done because coolant got into my oil.

A: Engines have many passages throughout the cylinder block, cylinder head, and often the intake manifold, for coolant to circulate. Heat is drawn from critical areas and brought to the radiator for release. Motor oil also circulates through smaller passages to spinning and sliding parts and is stored in the sump, or oil pan. The block, head, manifold, and other parts are joined with gaskets, which are supposed to keep everything separate. Gaskets can fail due to metal distortion (caused by excessive heat), corrosion of the metal surfaces, improper clamping force (broken or improperly tightened bolts), or less than careful installation. In rare cases cracks or warping of the metal housings may require their replacement as well.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at under-the-hood@earthlink.net.; he cannot make personal replies.

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