My car is leaking coolant. When I drive, it hisses from the cap, when its parked I see drops underneath the radiator tank and an unusual amount out of the exhaust. I also am noticing moisture where the exhaust manifold attaches to the engine. I’ve taken it a local shop, and they said all I need to do is change the tank. But why would it hiss out of the cap, or over heat when I’m driving even though its full? When the shop checked the engine light they said it was there because of a misfire. What does that have to do with the tank? Whats going on???!!!

What’s going on is that you probably need a better shop.

The only possible paths between the cooling system and the exhaust system are through breeched gaskets or through cracked metal walls (very rare on stock engines). The symptoms you have point to a very likely headgasket failure, wherein the hot combustion gasses are being blown into the water jacket when the cylinder fires and coolant is also being drawn into the cylinder during the intake stroke.

There are various ways to diagnose this, including checking the coolant for presence of hydrocarbons and (the best way) a pressure leakdown test where the cylinder is pressurized with air and a gage is monitored to see if the air is leaking out. Bubbles migrating up out of the coolant filler hole when the engine is rinning are also a real bad sign. Those would be the combustion gasses being blown through the coolant and finding their way out as bubbles (the filler cap is the highest point in the system, so teh bubbles go there).

You have a very serious problem that needs to be properly diagnosed and corrected. Hopefully it isn’t already too late. Hoepfully the head is not badly warped and/or a channel eroded into the head and/or block mating surfaces.


Very likely is a blown head gasket.

What this needs MB is ‘the old wrench’ method.

Just out of curiosity, what vehicle are we talking about?

Its a 2003 Ford Explorer XLT, it has around 150,000 miles, and the transmission was replaced once before we bought it. I think the radiator tank does have a small leak, but nothing very significant. I did use a bottle of that stuff you put in the coolant to temporarily patch leaks, and it worked for a week or two. Also, when our truck overheated yesterday, I opened the hood and it was hissing steam and coolant out of the resivoir cap.

If the head gasket IS breached the engine overheats and builds up pressure (more than usual) and forces the boiling coolant OUT.

Too be on the safe side I would have the head gasket checked out.