I have a cooling system leak in my 99 frontier 2.4 L. It is in the inside elbow of a 90 degree "pipe" coming off the manifold. How is this "pipe" removed for replacement?

Looks like you will have to have your HEATER-CORE replaced,your problem is the end result when a heater core goes bad.I think in your model,it is a significant job.

Where in the system is the 'pipe'.... Is it in the Upper Rad hose assembly, from the manifold to the top of the radiator? I *think* some of those had a two-piece upper radiator hose assembly, with a metal valve in between two hoses, the long one on the radiator-side and the short one on the manifold-side. I would imagine it's only got two bolts and maybe a third to retain the pipe to a bracket, but without looking at it myself, I'm not sure.

Metal "tube", not valve, I misspoke. Sorry.

Thanks for the response. The L "pipe" is connected directly to the manifold (metal to metal). The short leg of it connects to a U shape piece of hose that connects to a housing. (I'm assuming that's the thermostat but I could be wrong) This housing then connects to the either the upper or lower radiator hose. (I'm not sure as I'm not in front of it at this time) I'll double check it when I get home a get a detailed description. Thanks again for your help. I greatly appreciate it.

http://www.courtesyparts.com/frontier-parts-d22u-1998-2004/genuine-nissan-parts/exhaust-cooling/211-water-hose-piping/-c-2129_2130_2154_2158.html Here, you may find this helpful. Any time you want to take something apart and aren't quite sure how, your best bet is to start with Google Images and search for a schematic/diagram.... If you're unable to find any diagrams online, look for a parts microfiche. This will not only give you a detailed, expanded schematic but it will give you part numbers for everything from the elbows and hoses all the way down to a single bolt or nut. If still no luck, either find a friend that has a service resource such as ALLData, call your local parts stores and find one that has a service manual in stock for your vehicle (some parts shops like AutoZone will remove one from its packaging and let you look through it at no charge), or try the library

It is called a bypass hose so when the thermostat is closed your coolant can still circulate and disipate engine heat evenly until the coolant is too hot then themostat will open and closed To regulate the engine remperature. which the radiator hose is larger and has lower resistance the majority of coolant will take that route once it opens it connect the upper intake manifold

Can anyone answer this question

U have to remove the intake it looks like its a 4.6 hour job