Question on coolant lines around carbs

[Dadsun]

I'm converting my '73 240z's flat top carbs to round top SU carbs.  In the process, I'm sorting out, restoring/replacing coolant lines.

I found this topic while investigating whether or not to delete the manifold coolant pass-through.

But, my flat tops had some other stuff I'm trying to remove if not needed.  See this pic from that thread, with my mark-ups added in PURPLE and GREEN to show flat top elements I'd like to remove.

 

 

The green sensor is in the 2nd pic here:

 

 

QUESTION: Can I just get rid of this 5/8" hose and sensor altogether for round tops? That would only leave the coolant flowing through the intake manifold on that side of the engine compartment.

Edited December 12, 2020 by Dadsun

[Zed Head]

 

[Dadsun]

Are you answering me with my own quote? lol... that's a bit offsides.  😄

In the other thread, I was specifically asking about that sensor/valve and its removal.  But, the more I look at it, and see diagrams people have posted here of the round top coolant flow diagram, it seems the 5/8" hose is not necessary either. I was not sure if it was there to carry a higher volume of hot water around to the heater coil for climate control. 

[Zed Head]

I remembered your other post and was connecting them, for other people to see.  It's a common thing around various forums that multiple posts on essentially the same topic is "bad form".  But you can do it if you want to.

As opposed to bad form, good form is to supply pictures of what you're working on.  In your case, a 5/8" hose connecting to your thermostat housing would be huge.  Essentially like having a heater core hose connected there.  It would be something interesting to see.

And, for what it's worth, a thermostat would not normally be called a sensor.  And, are you sure it's a thermostat?  It might be a pressure relief valve.  Maybe that was covered in your other thread, I didn't read the whole thing, I just pasted the link, for convenience.

Whatever is going on there is unusual and might be an attempt to fix some other problem.

[Dadsun]

Well, it's all apart now, but I went and found an old picture.  The orange line traces the 5/8" hose.  The light blue circle is where the thermostat/sensor/pressure/valve/backflow preventor/whatever is.  I am calling it a sensor because someone said it may be that. I don't know what exactly it's purpose is. It's all new to me.

As for making a 2nd thread, sorry about that. My other thread is about the carb conversion, and this was specifically about this large hose that seems to complete the circle (in duplicate to the coolant intakes going through manifold) on that side of the engine bay. btw, that 5/8" hose was actually blocked because the brass elbow (can't see it well in the picture, but it's just below the blue circle) was completely clogged.

[Zed Head]

People do odd things to try to solve odd issues.  Sometimes based on a misunderstanding of how things work.  If you're going to round-tops and live down south I'd do what siteunseen/Cliff said in reply your other posts.  Those old pieces of heater hose will remain a mystery.

According to your diagram it's even worse than the typical heater core bypass.  What your diagram shows is taking hot coolant straight out of the thermostat, after it's traveled through the head collecting heat, just before it enters the radiator and running it back to the water pump with all of its heat.  Might be that somebody just connected a bunch of loose hoses together so they wouldn't flop around in the back of the truck.  Or maybe the engine is from the north and it's the equivalent of cardboard on the radiator.

Edited December 12, 2020 by Zed Head

[Dadsun]

The car has spent it's life in south Louisiana as far as I know. I bought it from the original owner last spring. I would bet, based on my experience digging into this car, that he had average Joe mechanic on this thing a lot.  Very little Z car expertise in our part of the country.  They had screwed up several things, including the wiring which caused the tach to stop working. Thankfully, this forum has helped me fix that and sort through this neglected car.

[Captain Obvious]

Take a read through this recent thread that talked a bunch about the same sort of stuff. There is discussion about the water lines and such that may help:

https://www.classiczcars.com/forums/topic/64432-260z-round-top-conversion-a-couple-questions/

 

[Freez74]

15 hours ago, Dadsun said:

The car has spent it's life in south Louisiana as far as I know. I bought it from the original owner last spring. I would bet, based on my experience digging into this car, that he had average Joe mechanic on this thing a lot.  Very little Z car expertise in our part of the country.  They had screwed up several things, including the wiring which caused the tach to stop working. Thankfully, this forum has helped me fix that and sort through this neglected car.

I live in south MS, so similar climate to you.  My car is a 74, so I think it  had similar coolant routing originally.  I installed 4 screw round tops with no water connection on the intake, blocked/removed every other coolant fitting and it's worked fine for years. 

[siteunseen]

The only drawback I've ever considered is the coolant cavitation that @240260280 spoke about but I never just jump in my Z and hit the road. I have my rituals that I do while it warms up enough to open the main thermostat. Also they live inside, never lower than 60F.

[DatsunZGuy]

I removed most of my coolant plumbing, SMOG equipment, and installed a euro balance tube to tidy up the engine bay.  Since the car is a fair weather plaything, it doesn't need to be setup for temperature extremes.

[jpc3006]

Dadsun,

FYI, when I replaced the flat-tops on my '73 with round-tops from a '71 many, many years ago I bought a new thermostat housing and the metal coolant tube that runs around the back of the head from the intake manifold for a 1971. This eliminates the part you call the "sensor" altogether and routes the coolant from the thermostat housing through the intake manifolds and back to the water pump.  Using the 1971 parts also eliminated the need to plug the extra connections as there is no provision for coolant being supplied to these carbs. I have run the car this way for over 35 years and have had no problems; so my answer to your 

"QUESTION: Can I just get rid of this 5/8" hose and sensor altogether for round tops? That would only leave the coolant flowing through the intake manifold on that side of the engine compartment." 

is yes, if you are installing 1971 round-tops as that is the stock configuration.