I own a 1997 Ford F-150 V8 4.6l. Problem is heat does not heat up like it should. I took it to a local garage to have the thermostat changed. I explained to the mechanic that within the past year I had my coolant system flushed and ever since then I have heard a swishing noise in the heating core. The mechanic told me that he discovered exhaust fumes in my radiator and did a dye test and found that there was carbon monoxide in my coolant. He also said that the swishing noise is air getting in to my coolant system. The mechanic said that it looks like I have a busted head gasket and that the head gasket needs to be replaced He did not replace the thermostat.
I thought that if you had a blown head gasket that the engine would be overheating; I do not have this problem. Before I pay for repairs I would like to know if anybody has heard this scenario and if I should look to replace the head gasket or if it is really just the thermostat. Yes, I have checked the coolant level. (205,000 miles)

 

My 97 blew a head gasket a couple years ago. The symptoms can vary depending on the severity and location of the damage to the gasket. If you have hydrocarbons in the coolant system then its a pretty good bet that one or both of the head gaskets are blown. The hydrocarbon test that your mechanic says he performed is the gold standard for detecting a damaged head gasket. If you have it repaired get both gaskets done at the same time. Removing both cyl heads is a lot easier than having to go back and remove all the components again later to replace the other gasket. Good luck.