Klayfish;
You know what I do for a living,insurance damage appraiser (autos). We asked the same question while in at a week long school in the early 90's.... Here's the whole scoop,I was there,saw it and did it,take it for what it's worth.....
The first day of class the instructor put four quart jars on his desk,one with water,one with gas,one with diesel,and the last with engine
oil. He then poured them approximately 1/3 full of sugar,put the lid on tight and shook them up real good,put them back on his desk and said for us to keep an eye on them and note what happens,also everytime someone got up and went in or out of the classroom and passed the desk he had to pick up at least one jar and give it a good shake as he passed......
A week later,sugar DOES NOT dissolve in gas,it actually sitcks together and looks like large snow flakes,in your gas tank it will "smother" the filter sock around the pickup tube and your engine will quit running for lack of fuel...
Sugar DOES NOT dissolve in diesel either,it just clumps up bigger than in gas..... Sugar DOES NOT dissolve in
oil either,it just turns to some thick looking molasse.....
Klay,when we run into this we pay to have the fuel tank removed and cleaned and the fuel lines flushed just in case,actually very inexpensive.....
Now here comes the best part,some of you guys are going to cuss me and call me a lair,but I don't care,these test were done and I was there and they were done to simulate real world experiences......
The instructor took a 5 pound bag sugar and the whole class went outside to the parking lot.... One of the grounds crew people went and got his personal 1983 Chev. p/u,350 4-v motor... Drove up to where we were,left it idling and the instructor poured half the 5 pound bag of sugar in the gas tank,truck kept running just fine..... One student said what if some sugar did fine a way past the filter or the truck had had the filter removed,teacher said he was waiting for that question as someone from every class will ask it..... Truck owner removes air filter and places it on the ground,instructor than begins to slowly pour 2.5 pounds of sugar down the carb,truck keeps on runnng just fine,even shut it off and poured a little bit down the carb then refired it,no problems,the only thing we found was that the exhaust sure smells a lot sweeter.... Afterwards the instructor told us they had been using that same truck for demonstrations for three years,about once a year they did have to take the gas tank off and flush it out as the sugar smothered the fuel pickup.......
So now you see putting sugar in the gas tank will not harm and engine in anyway shape or form other than stop up the fuel pickup.... Depending on the size of the tank and configuration,it should take at least 3 to 5 pounds of sugar to do that,some tanks a lot more.....
This is one time I truly can say the old saying;;;;;Been there,done that......
David