same 99 montero (gen II.5 montero).

after engine is hot, shut off, and then starts cooling, the lower radiator hose starts collapsing on itself as if under intense vacuum pressure. I am not a cooling system expert, but I don't think it is supposed to do that is it? I thought it is supposed to suck coolant back into radiator from overflow bottle but it doesn't appear to be doing that.

I have a brand new mitsu t-stat, brand new mitsu radiator cap, brand new mitsu overflow bottle, what gives???? also, I was looking at the rad cap, I understand how it pushes coolant out into the overflow tank, but I can't understand the physics of the cap that allows coolant to go back into the radiator from the bottle; anyone know how it does this?

lastly, I did check the tube from rad neck to overflow bottle and it is not plugged up.

what gives???

years ago I had a Toyo P.U. that did that, cap or thermostat.

Make sure the cap is good and it's the correct cap. I went through this a couple months ago. Also, make sure that the overflow line to the catch tank isn't plugged. I spent a week fighting with caps only to figure out (finally) that the line was plugged.

Edward

thanks for all the input so far, but:

it has new mitsu t-stat ordered by using VIN
it has new mitsu cap ordered by using VIN

lastly, I did verify that the tube going from rad neck to overflow bottle is not plugged (I was able to blow air through it easily)

anything else?

Mybe defective parts. I like those Stant , oh whatchamacallit, thermostats that are supposed to freeze open if they break...

these were all factory mitsu parts brand new ordered by VIN........which one would be the most likely to be defective? <img src="/forums/images/graemlins/confused.gif" alt="" />

Check your hoses Scott. I had the same problem with my Raider. Turns out the rubber was so worn down that they just couldn't hold a shape anymore. <img src="/forums/images/graemlins/kewl.gif" alt="" /> Also check for clogs in your hoses going to the overflow tank. (just read you already checked for clogs, ignore that) <img src="/forums/images/graemlins/kewl.gif" alt="" />

Hey Scottie, does the coolant level in the overflow tank go up when the truck is hot? Did you check the overflow tank lid passages are clear? What about where the overflow tank tube attaches to the rad neck, clear?

I would change the hoses next like Richard suggested.

As the fluid cools it creates a slight vacuum. It should pull fluid back in via the overflow.

I'm guessing the hose is so week it's easier to collapse than draw fluid back from the overflow. Replace the hoses both upper and lower. Also check to make sure there is no gunk in the bottom of your overflow preventing the reverse flow.

<img src="/forums/images/graemlins/patriot.gif" alt="" />

yes, all passages are clear, no gunk, all the way from bottom of pick up straw to rad neck.

the hose is extremely plyable, maybe it is worn down, after all, it is a 10 year old hose.

I have had a slight issue with air in the cooling system, could a weak hose cause that or would air in the system cause the hose to flatten?

thanks for all the input guys.