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Inspired by the Head cooling on cylinder #5 thread (http://forums.hybridz.org/topic/59029-head-cooling-on-cylinder-5-solutions/), I decided to make my own diagrams of the cooling system for US Z/ZX L6 engines. I had to exaggerate and diminish a few proportions to maintain decent flow while using a flat layout. These charts are as accurate as far as my knowledge and research have shown so far. I will gladly accept any corrections and update accordingly. The year cutoffs are approximate and do not reflect all of the small month-to-month changes of course. On the ZX diagrams, some cars got the throttle body heaters while others didn't. I left them in both diagrams just to cover all the bases. I did spend a fair bit of time on these, so if they do happen to find their way elsewhere on the web, make sure at the very least to cite where they came from.

 

Red = oil passages

Blue = water passages and flow direction

Yellow = direction of water flow in flexible hoses

 

1970-1974 240Z / 260Z

blue72_cooling_diagram_70-74.jpg

 

1975-1978 280Z

blue72_cooling_diagram_75-78.jpg

 

1979-1980 280ZX

blue72_cooling_diagram_79-80.jpg

 

1981-1983 280ZX

blue72_cooling_diagram_81-83.jpg

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On the 75-78 illustration, there is also an AAR mounting block coolant supply line like the throttle body heater in 79-80.  I think that it may also exist in the 79-83 engines also, maybe not.  My 95 Pathfinder still has an AAR.

 

Nice work, what did you use to draw them?

 

 

Anybody know the purpose of the pressure relief valve from 79 on?  Is it for pressure-actuated bypass of the heater core?  I wonder if a retrofit to early engines would be some cheap insurance.

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My understanding is incorrect! is that valve is temperature activated not pressure. It was used to speed warm up of the engine then closes as coolant temp comes up. It was described in one of the "do I loop my heater outlet" threads. I will double check my FSM when I get home.

Edited by ctc

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My understanding is that valve is temperature activated not pressure. It was used to speed warm up of the engine then closes as coolant temp comes up. It was described in one of the "do I loop my heater outlet" threads. I will double check my FSM when I get home.

 

I thought that too.  I have one that I pulled from a car in a junkyard and it actually is just a spring inside with a bit of plastic attached.  I even threw it in a pot of water and boiled it on the stovetop which did absolutely nothing.

 

NewZed, thanks for pointing that one out.  Just double checked the FSM and I'll make sure to add in the coolant passage at the base of the air regulator in that diagram.  It does appear that perhaps the very early 280Zs without webbing on the intake manifold didn't have that block through.

I used Illustrator for these files.

Edited by blue72

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I should have searched first...

 

From a Tony D post on Zcar
 
"The function is close, but not quite. It's a pressure relief valve that allows a bypass from the lower portion of the thermostat (back of the head) to the pump inlet when the engine is brought up to higher rpms before the engine thermostat is open. When the heater is on, or if the thermostat is open, the valve will never pop open.

It is a pump cavitation relieve device. This works in conjunction with the internal bypass on the right front of the block to the water pump inlet, and the 8mm line from the lower thermostat housing through the throttle body and to the water pump inlet. Those two lines are more than enough bypass to let the engine recirculate internally at fast idle and idle to warm the engine and get the thermostat open. The thermostat is also spring loaded to open under higher pressures---but this will be higher than cavitation point when cold, so on the later cars they added that valve. It is not necessary if you are letting your car warm up before running the rpms over 3000. Do that, and you will never notice anything.

If you insist on cranking the car up stone cold -40F, then jumping onto the highway at 80mph within 2 minutes (like I could do if it got to -40 here...) then this pop valve opening would likely keep you from cavitation on the water pump and housing, along with some overheating issues as a result of the errosion from same.

If you leave your heater valve cracked about 1/4, it flows similarly.

Knowing these tricks, you can function just fine without it. It's a nice 'idiot proof' device for the car, and god knows we need that with the group here... but a little intelligence in warmup or heater valve position and you will never notice it.

Don't tell me nobody here has ever noticed if they turn their heater to full "HOT" and left the fan "OFF" that the car will almost overheat? It warms up WAY faster like that! Why? 15mm of full open hose recirculating from the hottest back of the engine right to the water pump inlet. It can be so efficient the engine temperature can spike before hot water is circulating enough around the thermostat to open it! (especially if someone removed thermostatic control heat to the TB and or Manifold and didn't restore a proper bypass line to the bottom of the thermostat housing...)

Those lines are like Emissions Devices: Just take em off, the only reason they were there is because some guy's cousin had a factory making the parts and that's the way Japs design cars..."
 

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It is a pump cavitation relieve device.
 
It's a nice 'idiot proof' device for the car, and god knows we need that with the group here...

 

My memory dragged up the cavitation prevention concept after I posted.  I had read that same thread in the past.

 

Maybe I'll find one and retrofit............

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Made a bunch of small changes to the diagrams.  Looked at oodles of pictures and referred back to the FSMs to try and get the EFI stuff in the right order and with a decent label.

 

Does anyone out there know if the throttle body heater fitting was only produced for certain years of ZX or if it was more of a regional addition (something like a cold weather or emissions package) or something else entirely?

I have a '79 throttle body without it and an '83 throttle body that has it.  Curious to know if it was added for the '81-'83 cars or if it existed before 1981.

Edited by blue72

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Those diagrams are well done Blue72!

 

You do know that there are even more ways the water hoses et al were routed on L series engines? Cedrics had water from the water tap on the block under the manifolds at the rear of the block feeding the heater box in the cabin. I don't see this on any of the zeds. What does this mean? Dunno, apart from just pointing out variances and therefore options should one be required.  

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I'd love to do some for other L6 cars as well.  I am putting one together for my 510 (1600) at the moment.  Would just need to do the research and figure out all the varieties for the myriad markets.  Kinda interesting that the block coolant port got used in some applications.

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Cedrics had water from the water tap on the block under the manifolds at the rear of the block feeding the heater box in the cabin. I don't see this on any of the zeds. What does this mean? Dunno, apart from just pointing out variances and therefore options should one be required.  

Left side steering versus right side steering maybe?  From what I've read, things seem to fit together much better on the right side cars.

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Those diagrams are well done Blue72!

 

You do know that there are even more ways the water hoses et al were routed on L series engines? Cedrics had water from the water tap on the block under the manifolds at the rear of the block feeding the heater box in the cabin. I don't see this on any of the zeds. What does this mean? Dunno, apart from just pointing out variances and therefore options should one be required.  

It's a higher pressure area with more flow than the head. Depending on what Cedric you had as well. The 77 I had did not use what is sometimes referred to as "block drain plug" for the heating system. The smaller the heater core, the hotter the water you want to use....Cedric may have not 'needed' the head tap to get effective heating in it's HVAC system... I can't recall exactly, but I think I saw some US Sedans that used that tap with a "Y" branch... Can't remember the exact routing. Would be interesting to see a photo of the setups....my Cedric didn't have the 'aroudn the back' line like the Z"s did, either....it's bypass was totally at the front of the engine, with two 8mm tubes, and of course what came back from the heater core.

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On the 73 240z L28 project I'm just getting started on, behind the head by the firewall are just two hoses, one going into another. On other z's I've seen, there's a hard line running behind the head. Is this just a workaround someone did in the past when they were missing the hardline?

 

Also, how prone to failure are the heater cores and valves? Curious if I should replace them while the dash is currently out. Haven't pressurized the system yet to see if there are any leaks, about to order some hoses and curious if I should get a heater core/valve also. 

 

Photo%20Apr%2010%206%2007%2035%20PM_zps5

 

Photo%20Apr%2010%206%2024%2038%20PM_zpsj

Edited by Floorless240z

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Inspired by the Head cooling on cylinder #5 thread (http://forums.hybridz.org/topic/59029-head-cooling-on-cylinder-5-solutions/), I decided to make my own diagrams of the cooling system for US Z/ZX L6 engines. I had to exaggerate and diminish a few proportions to maintain decent flow while using a flat layout. These charts are as accurate as far as my knowledge and research have shown so far. I will gladly accept any corrections and update accordingly. The year cutoffs are approximate and do not reflect all of the small month-to-month changes of course. On the ZX diagrams, some cars got the throttle body heaters while others didn't. I left them in both diagrams just to cover all the bases. I did spend a fair bit of time on these, so if they do happen to find their way elsewhere on the web, make sure at the very least to cite where they came from.

 

Red = oil passages

Blue = water passages and flow direction

Yellow = direction of water flow in flexible hoses

 

1970-1974 240Z / 260Z

blue72_cooling_diagram_70-74.jpg

 

1975-1978 280Z

blue72_cooling_diagram_75-78.jpg

 

1979-1980 280ZX

blue72_cooling_diagram_79-80.jpg

 

1981-1983 280ZX

blue72_cooling_diagram_81-83.jpg

 

Can you post these images again?  Or anyone else.  I tried to PM you blue and you can't accept new PMs.

Edited by JSM

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I let my hosting lapse, but everything should be back up now. Looks like I've got some more old PMs to delete.

 

Can you post these images again?  Or anyone else.  I tried to PM you blue and you can't accept new PMs.

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