Coolant lines Collapsing. Help me figure out where to connect this vent line.

So I have a 95 tacoma 2.7l 4wd. I just finished rebuilding the engine and finally got it running. When i got back from my initial test drive, I noticed the radiator hoses had both collapsed and the coolant was a little lower.

The coolant could have just been the system burping (i haven't taken the time yet). But the collapsed hose was concerning. My drive was about 3 miles with 500ft elevation change. My best guess is that it has to do with this hose. I previously posted this picture and someone suggested that maybe it was a coolant hose. I'm pretty sure it is. the little metal cap on the end seems like its some sort of a breather valve or something. They only problem is that I can't find anywhere to plug it in. And as far as I can tell the FSM doesn't have any information on coolant line routing.

Thanks.

 

I have a 2000 2.7L 4wd 3rz-fe tacoma. I do not believe that the line you have pictured is a coolant line.
Usually, a capped line like that is a breather line for the differentials. You can see the pictures of my engine bay that I have attached and see where my breather line is.

 

Cool. Well that helps some. So you think the collapsed coolant lines could just be the elevation change a air bubble in the system?

 

The collapsed coolant hose could be because of a number of different things:
(I got this information from yourmechanic.com and am not taking credit)

The primary concern here is vacuum in the system created as the engine cools. If your radiator cap is not releasing pressure on the system, it can cause a vacuum to develop (coolant is unable to move to the reservoir/overflow tank). This can collapse the upper radiator hose.

Another potential issue is a blocked overflow hose. This will cause the same symptoms as a faulty radiator cap. There’s also the potential issue of a clog somewhere in the cooling system creating a vacuum and causing the hose to collapse on itself. However, the amount of vacuum created by a clog in the system is often not enough to collapse a new hose – it can be a sign that your hose is deteriorating and should be replaced.

Some hoses have wire reinforcement woven into the rubber of the body. If some of the reinforcement is faulty or broken, it creates a weak spot in the hose, and collapse can happen. If you have a collapsed hose, there’s definitely a problem in the system. The first suspect should be the radiator cap, and/or a faulty hose, but there are other possibilities that should be ruled out as well. A professional mechanic can help determine the actual underlying cause.