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Datsun 620 High Comp Engine Swap

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Mike's right. Connecting the two hoses together causes heat spots in the cooling system. It would be best to plug both of them and let the cooling passages in the block control the path of coolant.

 

You can get a 280zx water inlet (for the front cover) and plug the one tapped hole, then simply tap the head to NPT and plug that too.

 

280ZXwaterinlet.jpg

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I have a hose connecting from the back to the front lower radiator hose ... So what I have on my truck is wrong?

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In my opinion, yes.

 

This falls into the "splitting hairs" category, which this forum is famous for, but in a perfect world, you'd either have the stock setup with heater core installed, or both of them plugged.

 

If it's not a race car, you'll probably never know the difference.

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I was wondering what was gonna be said about this.. .. I have just a hose no heater core too.... It's a 5/8 hose so I planned to just shove a 5/8 plug in the hose to block flow... but I agree with distributor guy about circulation however if the hose is blocked by a heater core there's no flow during normal operation..

 

Scgreen620 have you had any problems with that hose connected not blocked?

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 .... however if the hose is blocked by a heater core there's no flow during normal operation..

 

Scgreen620 have you had any problems with that hose connected not blocked?

 

Correct. No flow in the summer when heater not used and weather is warmest. In the winter the heater core acts like a mini radiator. In severe over heating conditions you can roll the windows down and turn the heater on high to gain a small amount of cooling for the engine. Connecting the head to the pump inlet is simply diverting hot water around the rad. This just makes more work for the cooling system.

 

No it won't necessarily cause a problem but as stated, if the cooling system is stressed already in high temperature driving in traffic this sure does not help it any.

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The engine runs cooler when the heater is on.  In my experience the engine runs cooler when there is a hose connecting the two ports if there is no heater.  Can you plug them?  Yes you can.  I chose to spend the $3 on hose and hook them up.  Its certainly not life or death, but if your engine runs warm from time to time, this will help.  

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I was wondering what was gonna be said about this.. .. I have just a hose no heater core too.... It's a 5/8 hose so I planned to just shove a 5/8 plug in the hose to block flow... but I agree with distributor guy about circulation however if the hose is blocked by a heater core there's no flow during normal operation..

Scgreen620 have you had any problems with that hose connected not blocked?

 

So far the max my temp gauge has gone is to the middle and that's in 100 degree weather ...

 

Never thought it would be a problem ..

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The engine runs cooler when the heater is on.  In my experience the engine runs cooler when there is a hose connecting the two ports if there is no heater.  Can you plug them?  Yes you can.  I chose to spend the $3 on hose and hook them up.  Its certainly not life or death, but if your engine runs warm from time to time, this will help.

 

Wait so how is this bad if runs cooler ?

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Well since i have to drain the coolant to block it, I guess I won't bother till it matters.....

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Wait so how is this bad if runs cooler ?

Because it disrupts the flow of coolant as originally designed by the engineers. The coolant is meant to circulate evenly through the block from front to back and then up into the head where it goes back to front. Connecting the hoses changes that flow path which means that the cylinders do not cool at similar rates. With them connected, coolant runs straight to the back cylinder and the #2 and #3 cylinders run hotter than normal.

 

How does this affect things in real life? To quote Ghostbusters - "Fire and brimstone coming down from the skies! Rivers and seas boiling...Forty years of darkness! Earthquakes, volcanoes...The dead rising from the grave...Human sacrifice, dogs and cats living together... mass hysteria!"

 

But probably not cats and dogs living together.

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Looking closely at the coolant path, the lower radiator hose attachment that would normally suck on the heater core dumps coolant back into the pump to be distributed back into the block.  The rear heater hose connection would then be tempering the "cold" coolant at the pump and would be helping to pull more "cold" coolant to the rear of the block before its already heat soaked.  Then it gets pulled forward to the thermostat housing and pushed back into the radiator.  I'm failing to see how this is bad.  The rear of the engine is inherently hotter than the front.  Helping more coolant flow through it, well, cats and dogs living together.  It must be time to accept diversity?  I guess a digital thermal probe will tell before and after I clamp off the rubber hose.  Its something I can do Thurs while we're breaking in the cam.  My case will be skewed by the concrete block filler, but at least I'll know which way works best.  No assumptions.  

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"Fire and brimstone coming down from the skies! Rivers and seas boiling...Forty years of darkness! Earthquakes, volcanoes...The dead rising from the grave...Human sacrifice, dogs and cats living together... mass hysteria!"

 

But probably not cats and dogs living together.

 

Not so sure about that, looking at society today.......

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I think you guys may notice that I said it changes how the engineers designed it. I think a lot of theory goes into this level of design and it may be hard to prove one way or another. So go ahead and do what you will.

 

Cats and dogs... I have three outdoor cats strictly for the purpose of mousing. One of them think she's my dog's best friend. I think if she knew the truth, she might be hurt. I think it specifically states somewhere in the bible that cats and dogs living together is a mortal sin, or at least severely frowned upon. But since animals aren't allowed in heaven...?

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Looking closely at the coolant path, the lower radiator hose attachment that would normally suck on the heater core dumps coolant back into the pump to be distributed back into the block.  The rear heater hose connection would then be tempering the "cold" coolant at the pump and would be helping to pull more "cold" coolant to the rear of the block before its already heat soaked.  Then it gets pulled forward to the thermostat housing and pushed back into the radiator.  I'm failing to see how this is bad.  The rear of the engine is inherently hotter than the front.  Helping more coolant flow through it, well, cats and dogs living together.  It must be time to accept diversity?  I guess a digital thermal probe will tell before and after I clamp off the rubber hose.  Its something I can do Thurs while we're breaking in the cam.  My case will be skewed by the concrete block filler, but at least I'll know which way works best.  No assumptions.  

 

 

In normal operation the heater valve is open (usually in cooler weather) or closed. (all the rest of the time and specially in hot weather) So it's safe to say that all L series run in hot weather with that coolant connection closed.... and it works just fine this way.

 

If you connect the heater hoses together this would pull more coolant to the rear cylinder except for one thing. The water added to the cooler return rad water is already hot and uncooled. You have a closed circuit of hot water looping round and round. The returning rad water has to absorb this extra hot water and itself heats up slightly. If I said to block off 1/4 or your rad in the summer heat you would say that's crazy, but basically this is what is happening. When it gets really hot, in stop and go traffic having this much heat recycled past the rad could easily be the difference between boiling over and not.

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I see your point Mike, but only a small percentage of the water flowing through the block will be recycled.  There's still room for the water to absorb heat, and maybe 5% of the water the pump is pulling will be warm, not hot because it hasn't passed through the head yet - only the block.  The way I see it, it can only help to flow more water and absorb more heat.  The radiator will drop all the coolant that passes through it by 40 degrees or so.  Everything that can flow through the thermostat will get cooled.  Heat rises and the thermostat is at the top of the engine.  It'll all work out with maximum coolant flow and less likelyhood for hot spots in the head or the rear of the block.  

 

Its not like the same exact water is looping through the heater hose over and over, getting hotter and hotter.  Its stuff that was only half-way circulated, so it has helped to stabilize cylinder temps without affecting the head temps.  In the racing world, that keeps the cylinders and  therefor the main bearings more stationary and stable by not expanding and shifting at hot spots.  In a stock motor, this adds to long term durability.  Call it BS, but I'm running with it, the same way I use the heater to relieve heat problems in trouble-making motors.  It works.  

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Nissan must have made millions of these engines and none of them suffer from hot spots. If it was a concern the engineers would have made a by pass for the heater when it is shut off. I know of no other maker that has a heater without a shut off valve. Not quite as far as calling it BS yet. Do as you like on your race engine but I think it very ill advised to recycle heat back into the engine. When you say you use the heater to relieve heat problems in other engines... well this is the same amount of heat you are putting right back into yours. At least run these hoses to a heater core behind the grill so some cooling is done first.

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