There are small metal tubes under my hood, looks like they go the the radiator. they have a thick coat of rust so i replace them?what is their purpose?

 

photos would help.

 

Ill get some up tomorrow

 

For future reference, it's always a good idea to list the year of your vehicle/engine as well as what engine is in it. Things change a lot throughout the years/engines.

 

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The photos depict two different fluid-handling tubes. The one that runs from the neck of the radiator, across the top of it, and into the throttle body carries coolant to the throttle body to prevent icing in cold weather. The feed line to the throttle body is a rubber line that comes up from the water neck above the thermostat housing. The metal line in the photos is the return line back to the radiator.

The two at the left (driver's) side of the radiator that run into the top and bottom of the end tank carry transmission fluid through a separate chamber in the radiator to help cool the transmission. These two lines run back under the truck and into the side of the transmission.

Surface rust on either is not a major issue but if they begin to pit then its a good idea to replace them since the fluids inside (particularly the coolant lines) are under pressure and a ruptured line will make a mess among other things. If the rust isn't bad enough that the metal has begun to pit, I would recommend cleaning them really well and coating them in something like POR 15 or spraying them with a rust-inhibiting paint.

Welcome to FTE. Hope this helps.

 

Just word of caution, the transmission cooling lines like to rust solid to the fittings that connect them to the radiator. I have a 95 bronco and have found that any type freeze off penetrating oil works miracles, especially on fittings or bolts that have had exposure to long term heat. I am not a spokesperson just a very appreciative customer. That stuff saved my neck when i snapped two bolts on my water pump/timing chain.