I have a new Rad and cap in the montero 90 v6. The Lower hose colapes after tha car is run some. there is coolent in the resavor and the rad is low every time I look at it. If I open the rad cap it sucks air in to the sys. and the lower hose goes back to normal. I thought the rad resavor is there and that it should suck the coolent back in its like it just pushs in to there and never goes back in to the motor. I Dont think it has been burning the coolent no sign of white smoke for the pipe. seems to run just fine. any Ideas?

Incorrect/bad radiator cap or the overflow tank hose(s) is plugged up with crud.

But, you're correct - coolant recovery systems are supposed to work like this. When the engine gets warm coolant gets pushed past the cap into the recovery tank. When the engine cools a vacuum is created that sucks the 'excess' coolant back into the radiator.

If there is a problem, if the line is plugged or the cap doesn't let the coolant back in the vacuum created will collapse the upper and/or lower radiator hose(s).

There are two types of radiator caps - for systems with and without coolant recovery systems. I can't tell you how you'd tell which cap is which, except that some are labeled 'Vented' and these are allegedly for the systems with coolant recovery systems. I went through something similar with my new radiator a month ago - which uses a GM cap - and had to get the cap labeled 'Vented'. IÆve always bought my radiator caps for my Sport from the dealership so I have no idea what you'd look for at a parts store or if the import caps are even labeled.

Edward

Remove the radiator cap and look at the bottom side. There should me a brass disk (about the size of a dime) in the center of the rubber seal. Check if you can EASILY lift an edge of the brass disk with a fingernail. This disk is the valve that lets coolant back in the radiator as it cools.

If there is no brass disk, then you have the wrong radiator cap. If the disk doesn't lift easily a little, then the cap is defective. If the cap is OK, then check the overflow tank and the hose to it for a blockage (as Es 97Sport recommended)

I know the hose is not plugged I looked in to that I think the cap is not right. It goes on really hard. Wife cant get it on or off. I will get one for the dealer like $10 for it.

I had the problem before, Fixed it by replacing the old worn out coolant hoses. I found when the hoses break down from age they will suck in when the system starts to pull a vacuum.

The hose as about 6,000 miles on it.

It shouldn't be THAT hard to put the cap on. It's possible that's the wrong cap. After my experience last month trying to find the right cap for my new radiator I wouldn't even be slightly surprised. But, if you're sure that the coolant expansion tank hose is clear all the way through I'd try a different cap.

StockRaider is correct degraded hoses will cause this, too, but IMHO with only 6K miles its extremely unlikey. The upper and lower hoses on my Sport were on for several hundred thousand miles and even then I never had problems with them collapsing. However, I kept them clean. If they get oil soaked all bets are off.

Edward