1G Water Pipe/Thermostat Housing on a 2G

This is one of my favorite mods to do when I first get a 2G with an original 2G 7 bolt engine in it. Most of us have noticed that the design of the water pipe and thermostat housing on a 2G can cause a lot of stress when working with them. If you end up having to remove the water pipe whether it be to replace an o-ring or to replace the water pump, the 2G water pipe is a pain to remove and is even harder to put back together.

Text by AJ Hunsinger // Photos by AJ Hunsinger & Jason Drew


The reason the 2G water pipe is so hard to get in and out is because you are trying to connect each end of the water pipe to a solid source. One end goes into the water pump and the other end goes into the 2G thermostat housing. If you haven’t worked with the 2G water pipe very much it takes a bit to figure out how to get the sucker back on. You put one end of the pipe into the water pump, then can’t get the other end in the thermostat housing. Or vise versa.

NOTE: What I have found to work the best is to remove the 2G thermostat housing, put one end of the pipe into the water pump, put the other end in the thermostat housing, then bolt the thermostat housing back onto the head. But, that’s a lot of extra work.

With the 1G water pipe, you don’t have to worry about connecting the one end to the thermostat housing as the other end is where the lower radiator connects to.

The other downside to the 2G thermostat housing and water pipe is when you want to remove one, you have to remove the other. If you have to remove the thermostat housing, you will have to at least partially remove the water pipe. When doing this, you risk breaking the seal of one of the o-rings at each end of the water pipe.

waterpipe1

Switching to the 1G thermostat housing and water pipe is a huge advantage and will benefit you in the future when working with the water pipe or thermostat housing.

  • Much easier to remove, replace, or reinstall.
  • Only one o-ring (at the water pump).
  • Removing either the water pipe or thermostat housing doesn’t entail removing the other.

2G’s use (2) o-rings in the water pipe. One o-ring is placed in the end that goes into the water pump and the other o-ring goes on the end of the water pipe that goes into the thermostat housing. The 1G only uses (1) o-ring which is at the end that slides into the water pump.

NOTE: The 2G o-rings are the same as the 1G o-ring.

Now, using a 1G thermostat housing and water pipe on a 2G is by no means a direct swap. It does require some modifications. The first and most important is the routing of the turbo coolant lines. On a 2G, coolant is fed to the turbo but a line that is attached to the engine block via a banjo bolt and is returned to a fitting on the water pipe. On a 1G, the coolant is fed to the turbo via the thermostat housing and is returned via a line that threads into a fitting on the water pipe.

2glines

1glinesfeed

1glinesreturn

You are going to need to modify one of two things in regards to the turbo coolant lines.

  1. Block off the 2G feed by plugging the hole in the block.
    • Run a new feed from the thermostat housing.
  2. Block off the 1G return line by cutting the fitting off of the 1G water pipe and welding it shut.
    • Run a new return to the thermostat housing.

If you choose option 1, you need to plug the hole in the block using a 3/8″ BSPT plug. You will also need the 1G turbo coolant return line, or make one yourself.

option1plug

Another thing to note is to make sure you select a plug that is as flush to the block as possible. If not, the port on the 1G water pump will hit the plug and you wont be able to bolt the water pipe to the block. This is also the reason why if you choose option 2, you have to completely cut the port off of the water pipe. Otherwise, the port will hit the 2G banjo bolt that attaches the 2G feed line to the block as shown in the picture below.

clearance

A down side to using option 2 is that if you ever plan on going with a larger turbo like an HX35 for example, the turbo itself will hit the 2G banjo bolt that attaches the feed line to the block.

option2plug

Another benefit of using a 1g water pipe and thermostat housing on a 2G is that it makes the job of replacing the stock T25 turbo with a 14B, 16G, 20G, or any other TD05 turbo a lot easier since you already using the 1G turbo coolant line setup (if you selected option 1).

The bolt patterns between the 1G and 2G thermostat housings where they bolt to the cylinder head are different. BUT, a 1G thermostat housing CAN be used on a 2G head. A 2G thermostat housing, however, CAN NOT be bolted to a 1G head. The 2G thermostat housing has 4 bolt holes that forms a rectangular bolt pattern whereas the 1G housing uses only 3 bolts that form a triangle pattern. The part of the head that the 1G thermostat housing bolts to is the same on the 2G head. This is why the 1G housing can be used on the 2G head.

1g2ghead

Now, once everything is back together, you will notice that the 2G lower radiator hose will not work. The 2G lower radiator hose connects to the thermostat housing. On a 1G, the lower radiator hose connects to the water pipe.

Once you install the 1G lower radiator hose, you most likely will see that the hose makes contact with the counter-weight on the shift linkage of the transmission. You can cut the counter-weight completely off. This will not only give you the clearance you needed with the radiator hose, but you will also notice an improvement in shifting feel.

counterweight

List of parts needed to complete the swap:

  • 1G thermostat housing.
  • 1G water pipe.
  • 1G turbo coolant return line.
  • Several feet of 3/8″ rubber hose to make up additional length of feed line as needed.
  • (1) new water pipe o-ring.
  • 1G thermostat housing to head gasket, or make your own, or use silicone/RTV.
  • 1G lower radiator hose.

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