Ethanol to blame?

More specifically the vehicle is a 2003 F150 4.2L V6 and my question is the bogosity of the answer my mechanic gave me in explaining how a $29.99 oil change turned into an $800 repair. It began when he noticed foamy residue on the underside of the oil filler cap, indicative of a possible leak of coolant into the engine. The proposed remedy was to replace the upper and lower intake manifold gaskets. The gasket kit was ordered and the remedy applied. However, upon removing the covers the mechanic discovered that the intake ports were nearly completely plugged with a black sticky substance which he said could lead to overheating and a blown engine. It took 16 hrs. to remove said substance, hence the $800 repair. The mechanic said the presence of the substance was due to the ethanol in the 87 octane gasoline and suggested using mid-grade or premium to prevent future buildup. Bogus?

If one grade has ethanol, they all do, typically. Can’t speak to the tarry stuff.

What was estimated charge to change intake gaskets? A whole lot less than your final 800 charge? Most shops charge a pretty hefty bill for intake gaskets. U make it sound like original bill was 300 and final bill was 800

That black sticky gunk isn’t from the ethanol. It’s from the coolant getting drawn into the intake ports and mixing with the fuel being sprayed by the port injectors and subjected to the heat around the valves…combined with oil getting drawn in onto the valves as well, perhaps from leaky valve stem seals. High test fuel won’t make a difference.

What tests did he do before prescribing new manifold gaskets? Did he so any tests for the headgaskets?

How many miles are on this puppy?

The $800 repair bill seems fair to me. Increasing the octane level of your fuel will have no effect other than costing you more.

It seems fair to me too under the circumstances, as long as the shop actually showed the problems to the OP and discussed them, which it appears he did, but I can understand the OP’s shock and doubt. Haveing a $29 oil change turn into an $800 job would stun even the toughest of us.

Stoveguyy, you missed a decimal point in there. The original bill was a $29.99 oil change, not $300. the same mountainbike got it right. The mechanic did not test the head gaskets and replacing the manifold gaskets was an intuitive, experienced-based call. The truck has 55,000 miles on it.