My husband and I are trying to get to our thermostat to change in my 2002 rendezvous, but there is a metal pipe in the way that we can't figure out how to remove. just behind the pipe, is a metal plate that will also need to be removed. Any ideas?

It is the exhaust pipe that goes from the front to the back of the engine above the bellhousing. The thermostat should be where the top radiator hose connects to the engine.

Links below to how and change thermostat
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How To Fix Replace Thermostat GM 3400 Aztek Rendezvous Alero Grand Am...

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2002 Buick Rendezvous Changing Thermostat on 2002 Buick CX

On the back side bottom left of the radiator is a drain plug ! you'll need to crawl underneath to see it . They are usually white in color !

I can't tell you for sure, may be you can tell me? do you think you can get the metal pipes out, the rubber hoses are designed to be serviceable, metal pipes are not. In saying this if you can get them out, good remembering that these metal pipes are normally bolted to the motor to stop vibration, you will need this pipe from your dearer and don't forget your rust inhibiter, very important

You will need to remove your air cleaner and duct assembly. You will then see the thermostat housing sandwiched between the back of the intake manifold and the exhaust crossover pipe. The service manual says to remove the exhaust crossover pipe, but trust me, you do not want to attempt this unless you have access to a torch to heat the nuts that hold the thing to the exhaust manifolds. If you break a stud, then you are going to be removing an exhaust manifold for broken stud removal. If you take the 8mm screws out of the heat shield on the exhaust crossover pipe, you can wiggle the heat shield out. This will provide enough room to get the lower thermostat housing bolt out. It is a pain to do it this way, but it works and will prevent broken exhaust pipe studs. Sometimes the little 8mm bolts will also break, but since they only hold the heat shield, it is of no great consequence.

Then all you have to do is remove the two bolts that hold the thermostat housing to the manifold. The thermostat is directly under it.
Then the only other real "trick" is getting the thermostat and O-ring to stay in the correct position while you put the thermostat bolts back in. A trick that I use is a small wooden wedge. I put the thermostat housing into place over the thermostat and O-ring, then place mt wedge between the thermostat housing and the crossover pipe to hold the thermostat housing in place while I start the bolts. Otherwise, the thermostat tends to slide out the bottom while you are trying to get the bolts started.

Let me know how it goes...

P0401 Egr Flow Insufficient
try cleaning the EGR hose.

head gasket it sounds like you have a warped head antifreeze burns white remove and have it milled and magnafluxed to check for cracks that will core your problem

the thermostat is located at the end of the big hose that is on the right side when you are standing in front of your vehicle you going have a hard time with one of the 2 bolts on thermostat housing you going have to loose the pipe that has a valve that comes out of the watter pump in order to get to the2 bolts in thermostat housing

Thermostat Removal & Installation 3.4L & 3.5L Engine To Remove:

1. Drain the coolant below the level of the thermostat.
2. Remove the air cleaner and duct assembly.
3. Remove the exhaust crossover pipe.
4. Disconnect the radiator hose from the thermostat housing.
   
   
5. Remove the mounting bolts and remove the thermostat housing.
6. Remove the housing gasket.
7. Remove the thermostat.
8. Clean the mating surfaces.

To Install:

1. Install the thermostat on the engine. NOTE: Apply RTV sealer to the thermostat housing bolt threads.
   
2. Install the thermostat housing and gasket with the mounting bolts. Tighten 18 ft-lb (25 Nm).
3. Connect the radiator hose to the thermostat housing.
4. Install the exhaust crossover pipe.
5. Install the air cleaner and duct assembly.
6. Fill the cooling system.
7. Check the cooling system for leaks.

3.6L Engine To Remove:

1. Remove the air cleaner.
2. Remove the throttle body.
3. Remove the heater pipes.
4. Remove the coolant inlet pipe. Thermostat 3.6L
   
   
5. Remove the thermostat mounting bolts and remove the thermostat.
6. Clean the thermostat and heater pipe mating surfaces.

To Install:

1. Place the thermostat in the housing with a new gasket.
2. Install the thermostat and gasket on the engine with the mounting bolts. Tighten 89 in-lb (10 Nm).
3. Install the coolant inlet pipe.
4. Install the heater pipes.
5. Install the throttle body.
6. Install the air cleaner.
7. Fill the cooling system and perform a leak test.

first check to make sure the cooling system is not air bound,takes a while to bleed off the air,try this and get back to me Thanks Ray