I don’t think it’s relevant to this question but just Incase, I’m currently switching from flat tops to round tops on my 260z. 
 

I've done some reading on the matter but reading too much I find that I kinda get too much information and start to second guess what previously seemed like good information. 
 

So, common issue I hear, leaking coolant tube between the intake manifolds. 
A seemingly good idea I’ve read is to just bypass the intakes by putting a hose straight from the thermostat to the hardline at the rear of the engine. Can anyone tell me if this is a terribly bad idea?

 

I have a basic understanding of why the water is run through the intakes i think, to my understanding there might be a slight difference when the engine is cold... 

 

Not to beat a dead horse of a question, apologies. 

There is no such thing as a dumb question, except for the one not googled ;). As google doesn’t tell you a lot about this, then this is a good question! :D

 

I have read that the idea was to keep the manifold at a constant temp, improve cold start by heating up the mix and help with atomisation, stop them icing up in the winter - blah blah blah and furthermore blah.

 

In short, it was one of the best things I did to mine. The carbs run “fridge cold” to the touch after a good hard blast around. There is less heat soak and related issues when you stop for fuel on a hot day. Fewer points of failure and leaks (mine was leaking from every possible point).

 

Unless you are driving your car in a subzero winter and worried about carbs icing up, then my advice is take it off. A cool carb is a happy carb and performs better, giving better responsiveness and HP. Oh and it saves weight!!! Every gramme counts, that is why I shave (face and other bits) before I go for a drive!!

 

Not to mention a cleaner engine bay. Here’s a recent photo from when I was testing longer velocity stacks ...

 

 

It’s intent is to warm the carbs when the engine is cold, to improve drivability and reduce emissions. It was found with the issues around heat soak and vapor lock that they wanted to turn that hot water source off so they added a heat activated valve at the back of the last carb to turn the hot water off once the engine was fully warmed. No need to heat the carbs once the whole thing is all toasty. You can see the 73 version in your picture above just behind the red circle. 

The early Z’s had that line with no restriction. 

The common thing to do is just lose that coolant line altogether and, if you drive in cool weather, put up with maybe slightly poorer drivability until the car warms up. If you want to keep all the lines and such for nice correct appearance and ease of plumbing, then I’d plug the line internally at some hose connection and get the best of both worlds

Edited October 13, 20204 yr by zKars

I deleted mine and all the potential leak spots.

Best thing I've ever done too. One of the best things.

Ceramic header ranks waaay up there...

Talk about chilly carbs! No coolant flow and the ceramic header puts a light frost on my domes. Cooler fuel is best, look at all the people that run nitrous.

 

Edited October 13, 20204 yr by siteunseen

1 hour ago, Cooper260z said:

A seemingly good idea I’ve read is to just bypass the intakes by putting a hose straight from the thermostat to the hardline at the rear of the engine. Can anyone tell me if this is a terribly bad idea?

Enjoy the weird words, an ad somehow got incorporated and blended in to my quote of your words.  Like The Fly.  Something for you @Mike, not a big deal, just a little light.

One thing you might do is to put a restriction in the line.  The only purpose of that flow once you take the carbs out of the picture will be to heat the thermostat and it won't take much.  And you might not even need that if your thermostat has the small bypass hole to accomplish the same purpose.  Otherwise, like when bypassing the heater core, that flow does not cool the head like it should.  It bypasses it, and in effect, reduces water pump volume.

Just a thought.  You need all the cooling you can get.

Edit - I'm a slow writer.

 

Edited October 13, 20204 yr by Zed Head

@AK260 nice setup! AN lines will hopefully be in my future! 
 

@Zed Head if I’m understanding you correctly, you’re saying I should a keep a line there to retain the flow of water? Which is my thought on the matter, that more water moving is kinda better for cooling purposes? Which is why I want to keep a line there, just add like a rubber hose to effectively replace the hardline between the manifolds that is rusting and leaking. 
 

Though I guess completely deleting the that water passage is an option as per what @zKars And @AK260 said which is interesting as seemingly that line isn’t crucial to the circulation of the coolant. 
 

And as another note, I’m in California’s SF Bay Area so i don’t think I could drive in frigid temperatures unless I REALLY tried hard to get to them, so I don’t think the temperature of the carburetors will be an issue 
 

I'm just saying be aware of unintended consequences.  The original line has a thermostat in it, which would be a restriction.  If you just run a straight line you might create substantial flow that doesn't do much cooling.  Think about the flow path of the coolant.  It's supposed to travel past hot surfaces before going to the radiator.  If it doesn't it's just wasted pump volume.

You need a small amount of flow past the closed thermostat valve so that the wax pellet will see the hot water and open.  Most thermostats have a small hole to do that.  You're probably fine, and neater, just blocking the ports.

Okay, so the theory is that because of the inline thermostat, once the engine is warm water doesn’t flow through the intake line anymore, it only flows through when the engine Is cold. So by deleting that line it will only have an effect on the engine while it’s cold and once it’s warm there’s no difference.  Basically?

The reality is the thermostats on the rear intake "in" are now unoperable and irreplaceable.

Actually, if you consider the thermostat as a "block" that kind of answers the whole question.  Blocking it is just like having the thermostat closed.  In that little cooling line only, not the main thermostat.  Running a "bypass" is the common error when people get in to those types o lines, like for the heater core.  Bypasses serve no purpose.

I vote for blockage.

The only janky thing is the plugging you'll have to come up with for the coolant that runs under the spark plugs that hooks to the hardline behind the cylinder head. I put a steel threaded plug in mine with a hose clamp. I don't care though, it's no show car. Function over fashion.

@siteunseen Are you saying to plug the line on the spark plug side of the engine (Pictured?) I was thinking to plug it just behind the intake manifold. but on the other side would be a bit cleaner I suppose. Doing that would also stop the water from flowing through the balance tube, which I don’t believe is an issue since earlier cars didn’t have it that way, but I could be wrong. 

You could just run a new piece of hose and get rid of the T (Y) entirely.  Every plug is a potential leak.  And if those braided hoses are original they're ready to blow. 

The coolant lines to the heater core are probably the most common cause of overheating.  I think I just saw two stories about it on the forum, and I have my own story, coming up the Highway 26 hill at night, and not noticing that my temperature gauge was pegged out until I got to the top.  Close enough to home to just keep going and hope.  The heater core hose had split and was blowing steam by the time I got home.  It survived but I was never really sure it hadn't made my head gasket coolant leak worse.  Anyway, those old braided hoses are dangerous.