240z Coolant bypass mod (contains pics and part numbers)

[big2003viper]

So, after buying my 73 240z and putting in a new motor (the old one was  beyond repair), I needed to figure out the hose routing from the thermostat housing to the intake manifold. The intake and carbs are from a 70 - 72 240z, but the outlet fitting was one from a 260z that had 2 of the 3 ports soldered shut. Instead of just getting a nipple fitting and a hose, I decided to do something a little different. This might help someone in a similar situation or if you convert to SU carbs and still have the  Hitachi carb thermostat housing. I started off by finding the threads on the thermostat housing. They're 1/2" NPT. So I got a 1/2" NPT to -6AN adapter (PN: SUM-220649). For the intake fittings, they are 1/2" inverted flare (IF). So I got a 1/2-20 IF to -6AN adapter (PN: SUM-220668). Then, to connect them, I got a pair of -6AN to tube adapter fitting. After than, I got a piece of stainless steel tube in 3/8".

 

 

The tools needed are a tubing cutter, a tube bender, and a fine tip sharpy.

 

Here's the end result. As you can see, there's plenty of clearance for the distributor and plug wires. I started with a 90 degree fitting from the thermostat housing but it turned out that the angle is too extreme.

 

I hope this has been helpful. Any questions, feel free to ask.

Edited March 27, 2015 by RB26powered74zcar

[NewZed]

. I started off by finding the threads on the thermostat housing. They're 1/2" NPT. So I got a 1/2" NPT to -6AN adapter (PN: SUM-220649)

I don't think that Nissan ever used SAE threads.  Metric or BSPT all the way from what I understand.  The dripping JB weld makes one think that you may have realized something was off. 

[big2003viper]

That's not JB weld. It's some pipe sealant that I found in my garage. Both of the fittings threaded into the ports and tightened just fine. FYI, the TPI for BSPT in 1/4" is 19. The port in the manifold is 20 TPI.

Edited March 27, 2015 by big2003viper

[NewZed]

You might be able to thread a 1/2" NPT fitting in there, but that's not the design spec.  FYI.

[big2003viper]

Either way, it works. If BSPT to AN adapters were available, I would try them. But alas, they are not.

[nullbound]

Motamec makes BSPT to AN adapters.  There are other companies that do, as well.  However, I believe all the fittings for the thermostat housing are metric.  The temp sending unit is M16 x 1.5, for example.

[Tony D]

Either way, it works. If BSPT to AN adapters were available, I would try them. But alas, they are not.

They are, actually. I bought one in brass, and one in SS from the local Swagelock Distributor. They have Adaptors for most anything NPT, ISO, AN, Metric, etc.... I went in initially for an NPT to 1/4" Thermocouple adapter....found out with their gauging it was NPT to a 10mm Thermocouple! They had that there, in stock, as well! Distribution worldwide on local level, and shipping to you from the local branch stateside.

 

What is the bend radius on your bender? (Should be on the saddle portion.) I can't remember mine, but that radius is critical for getting the nice line-up you got on your adaptation.

 

I like Loctite PST for thread sealing on NPT. On a 1/2" NPT about 3/4 turn from finger tight is all you need to effect a proper seal. On elbows than require positioning that flexibility makes it nice.