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I own a 1996 Chevy S-10 extended cab truck with the 4.3 V6 engine. It currently has just under 96,000 miles on it. I use it for rural mail delivery in the Southport/Sunny Hills area. I am a long-time listener to your weekend radio show I have heard you advocating putting in synthetic fluid, which should give you between a 7-12% increase in mpg (I am getting 13.1 - 15 mpg). I was told a while back by a good friend (who is a technician) that changing to a synthetic transmission fluid could cause me to start having transmission fluid leaks. I certainly want my vehicle to last as long as it can. I am diligent about keeping fresh fluids in the truck. Would I just be better off not taking the chance of leaks forming and keeping the same fluid in there? Also, I'm getting ready to change out the radiator, coolant recovery tank and water hoses (water pump is just a year old). Is there anything special I need to do to flush out the system to get as much junk out? My current radiator and recovery tank has that brown gunk in it (I believe the nylon 6.6 you mention on the radio). I know I've dropped a lot on you here, but this is all I'm worried about at the moment. I appreciate your show and plan on being a long-time listener.

Let me tackle the first question about going to synthetic fluids causing engines and transmissions to leak. Years ago (in the 60’s & 70's) synthetic fluids were "Ester Based". Ester Based lubricants did cause some engines seals of that era to leak. The seals themselves had inferior elastomers in the make up of the seal. Today’s seals can handle synthetic fluid because of their improved composition. Today’s synthetic fluids are NOT “Ester Based” so this has been taken out of the equation. So to answer your question "Will synthetic fluid cause seals to leak/" the answer is NO! If they are not leaking now they won't leak when you use synthetic fluids. Now to the gas mileage savings of 7 to 12%. This figure is for a PROPERLY running vehicle that has good emission readings coming out the tailpipe. If your vehicle is NOT running well, it would be a waste of money to change to synthetic fluids BEFORE you have the vehicle running properly. If you do change the engine oil, transmission fluid, transfer case, differentials all to synthetic fluids. You will see an increase in fuel mileage of 7 to 12%. Now to your cooling system question about the “Brown Gunk”. The "Brown Gunk” is due to Nylon 6.6 breaking down that has been exacerbated by adding water other than "distilled water" to the cooling system. If you do plan on doing all this work remove the thermostat and pressure flush the block backwards and forwards several times. This is to remove built-up "gunk" in the corners of the cooling system. After you put the cooling system back together, find a shop that will do a "coolant exchange" with a “coolant exchange machine”. This will remove 96 to 98% of the old coolant insuring a proper mixture of extended life antifreeze and distilled water. DO NOT USE GREEN SILICA BASED ANTIFREEZE. Your engine is not designed for this type antifreeze and damage may occur down the road.


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