I have a 1986 F150 with the 6 cyl engine. Every time I shut off the engine the coolant runs out of the overflow hose. There is no recovery bottle and it appears it never had one. What is causing this or should I should I install a recovery bottle? Thanks, Mark

 

That is actually rather common if your toping it off, you should add a bottle. It's also made worse by worn hoses.

 

You need to let it overflow, and then later after it's cooled off, take the cap off and look at the coolant level. It should be down a little bit below the cap. On a really hot day or when you get the engine really hot, it may overflow a little more.

If you do not run a recovery bottle, you have to leave a air space in the top of the radiator to leave room for the coolant to expand. That's why they started using overflow bottles, so they could run the radiator completely full.

Also the lower the pound cap, the more air space you have to leave.

 

Just a little more detail on the why. As coolant flows through a running engine, the heat goes from the engine into the coolant because the coolant isn't as hot as the engine. Then the coolant goes to the radiator where it transfers heat to the cooler radiator. When you shut the engine off the engine is still hotter than the coolant, but now the coolant isn't flowing and no air is going through the radiator, so it's not getting cooled off as much. So the coolant gets hotter (it's called "heat soaking"). A the coolant heats up it expands, as it expands it needs to go somewhere, so it goes out the overflow tube.

If that tube goes into a recovery bottle the coolant is captured, otherwise it's just dumped. Then as the coolant in the engine and radiator eventually cools off it contracts. as it does it sucks whatever it can back in through the overflow tube. If there's a recovery bottle (that isn't empty) it will suck the coolant back in, otherwise it sucks air in.

By the way, this happens with the engine running too. If you completely fill your radiator cold and then start the engine coolant will start coming out of the overflow tube as it heats up. It's just sometimes surprising to people that the coolant keeps heating up after the engine is shut off.

 

My 86's overflow bottle is the front side of the windshield washer tank on the driver inner fender well.

I'm guessing your truck doesn't have that ?

 

It's also possible that your radiator cap spring is getting weak, or the cap has a lower than original lb/psi rating.

Either of these make it more likely to overflow, when turned off.