Looking closer at the parts book I noticed that 9/71 was also when three screw SU's were added and it seems that was when cooling passages were added to the base of the carbs. I did a bit of searching here and found this topic:  http://www.classiczcars.com/topic/18629-4-screw-sus-and-the-coolant-heated-manifold/

See post 2 by Arne.

The investigation continues.....

The 72 carbs were different than the previous years in that they actually had coolant passageways in the body casting that directed water out of the intake manifolds and up closer to the fuel nozzle. Previous years only had coolant flowing in the intake manifolds, but in 72, they went that extra step and tried to get that flow closer to the needle and nozzle. You can tell the difference with 72 manifolds, carbs, spacers, and gaskets which all have holes in the faces to pass the flow.

Datsun seemed to like the results too as evidenced by the fact that they improved on this practice into 73 and 74 with the flat top carbs as well.

At this point, I believe that the key questions to be resolved are:

 

Is there are retired cooling system engineer in the audience?

1. Was the Manifold Thermostat actually installed on pre-72 Z's?  (no speculation - we need a clear picture of the engine compartment of a guaranteed-original 70 or 71)
    
2. If the Manifold Thermostat is removed to make the manifold heat circuit operate full-time, what are the coolant flow characteristics through this circuit (i.e. hi v. lo vs. no volume; front-to-rear vs. rear-to-front flow direction)...
   
   - under cold-engine conditions?
   
   - under hot-engine operating conditions?
    
3. For Z's equipped with the Manifold Thermostat, does removing this thermostat (assuming that it's suspect) cause negative issues somewhere else in the cooling system?

On ‎1‎/‎13‎/‎2016 at 4:23 AM, Namerow said:

At this point, I believe that the key questions to be resolved are:

 

 

1. Was the Manifold Thermostat actually installed on pre-72 Z's?  (no speculation - we need a clear picture of the engine compartment of a guaranteed-original 70 or 71)

This is a page from a 1970 sales brochure, to me it looks like engine pictured does not have an intake manifold thermostat. By the position of the small hose over the heat shield it does not look like there would be enough room for the thermostat.  Pictures I have seen with the thermostat have that small hose extending beyond the heat shield as in the picture below of Jalex's '72. Just my opinion.

Mike

 

Found this, from the ZTherapy guys, they mention the difference.  Thought that they would have chimed in on one of these threads - http://www.ztherapy.com/technical_stuff/spotterguides/zcar/240spotter.htm

Actually, they mention just warm water but not the thermostat.  Maybe the whole process was two steps: one to get the warm water in, then the thermostat to fix the new problem it caused.

I had also found an image of a 1970 intake manifold that seemed to have the fluid passages cast in but no fittings attached.

Edited January 18, 20169 yr by Zed Head

@ CanTechZ - I had looked at exactly the same picture in the 70 sales brochure, but the image file that I was using wasn't high enough in resolution to let me zoom in on the back of the engine.  Yours is, and I agree with your conclusion.  At least, to an extent.  Sales brochures are usually printed a long time before a new model actually hits the showroom floor, and the vehicles used for the shoots may or may not be 100% faithful to the final production version re the odd small detail.

BTW, it was fun to see in that picture how those cloth-braided ho$es came pre-frayed from the factory!

@ Zed Head - Once again, I had looked at the same picture -- this time on the Z-Therapy site  The caption on the picture of the 70-71 intake manifold is misleading.  It says, "1970-71 non-water heated", despite the fact that the coolant pipes for manifold heating are clearly visible.  Of course, what Z-Therapy are really talking about is non-water-heated carburetors, not manifolds, and in that respect they are absolutely correct: the 1970-71 carbs are not water-heated because the water-heating cavities in the manifolds -- which are there -- are not ported out to the carb bodies.

I think that your take on the evolution of the whole manifold/carb-heating system is probably right.  It went in steps: first, the obvious/easiest step of heating the manifolds, then the fix-up via the addition of the thermostat, then the improvement by adding carb heating.

We're still left with the question of when the Manifold Thermostat was added to the design (and neither CarPartsManual.com nor the FSM's nor the TSB's seem to offer a definitive answer).  Was it added on the fly at some point during 70-71 production, or did it arrive in conjunction with the carb heating feature in 72? 

Maybe Chickenman, c/o his Nissan Service background, has the answer...

If someone really wanted coolant control through the carbs, one of these could be rigged to work, I think.  180 might be high but depending on where it was mounted, actual temperature through the carbs could be lower.  There might be other temperature specs. out there also.

http://www.amazon.com/Derale-13011-Fluid-Control-Thermostat/dp/B004XONNRQ

http://www.improvedracing.com/oil-thermostats/high-flow-engine-oil-cooler-thermostat-185f-p-212.html

A solenoid valve with a temperature-controlled electrical switch would work also.  BMW has some low T switches, for their cooling systems.

Hi guys, I have a workshop with a lot of obsolete stock on my shelves after about 40 years trading.  I have a brand new valve, still in the Nissan box - P/N 14100-E8850.  I'm an old fella & not savvy enough to post a pic, but it's mint, still has the thread coating on. If you're interested, email me at automobilia@bigpond.com.  Cheers, Nev. 

So bottomline. Will my car performance be affected if i remove the Manifold Heat Control Thermostat considering that the temperature in Panama is 33°C as i already removed it and plugged the lines as shown. Problem is that now the car takes longer to warm up and need to leave the choke longer. I was having fuel percolation issues and needed to be able to use the car in traffic jams without stalling issues.

Switched from e88 intakes to n33's also new header. Noticed the manifold heat control thermostat.  Opened it up and saw that it was a thermostat. It's been two weeks since the rebuild. Runs amazing. But after warm-up get an occasional studder on take off. Could a stuck open manifold thermostat cause the hesitation on take off? 

 

Remnant,

can't help you with the thermostat problem but your engine bay is gorgeous, is that a permanently mounted vacuum gauge on the balance tube, love it.

Thanks...yes welded up all the smog ports but one and added a vacuum guage.