280ZX Heater Valve Repair - Page 2 - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #11 of 23 (permalink) Old 12-06-2012, 10:12 AM
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You should change the title of the Sticky to "280ZX Heater Vavle Repair" since it deals specifically with that model.
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post #12 of 23 (permalink) Old 12-28-2012, 10:38 AM
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has anyone tried this in a older z like a 76? the Nissan part that is i ordered one today any info would be great thanks
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post #13 of 23 (permalink) Old 02-12-2013, 04:17 PM
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Originally Posted by palladin View Post
Merry Christmas...
Palladin;
VERY GOOD info on replacement/refurbishing the valve. Much thanks -- derek
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post #14 of 23 (permalink) Old 02-15-2013, 02:29 PM
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Question 1982 280ZX NonT Heater bypass??

Hey y'all. I would like to know, Is it crucial to the non-overheat of my car to fix the heater by-pass job that the POs did. I say yes but the Mercedes mechanic doing some work on my car says it makes no difference it has nothing to do with overheat. So.....????
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post #15 of 23 (permalink) Old 02-15-2013, 05:04 PM
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It's been shown that the heater passages should be blocked if the heater core is not in-line, not connected together as a bypass. The bypass lets coolant that would normally travel through the head go straight back to the water pump, reducing flow through the head, especially the rear cylinders. Tony D actually did some work and took measurements to show this (search Tony D and heater core bypass and you might find it, I think he posted results on this forum). Blocking the passages forces the coolant through the head, bypassing lets it avoid the head.

I don't know if it's crucial but it could be a factor.

Also, the impellers on the old water pumps have been known to corrode away, something to check.
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post #16 of 23 (permalink) Old 02-15-2013, 05:08 PM
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Bah, PDX beat me to it:

Critical.

I believe Tony D proved this with one of his engine dyno runs. I remember seeing pictures showing the glowing bright red exhaust manifold.

Search for it and ye shall find:

Looping the Heater Hose

1982 280zx N/A 2+2
MT w/t-tops and hopefully no more mice
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Last edited by jewelz; 02-15-2013 at 05:09 PM. Reason: Intake not exhaust~
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post #17 of 23 (permalink) Old 03-02-2013, 05:28 PM
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Merry Christmas...
Another trick I thought I would share with you ZXT owners. If you vacuum pump goes bad, as my did twice...just old from running all those years, go to your Ford Dealer or order the replacement part for a Ford 250 Superduty vacuum pump. That is if you want you AC and heat when you floor your car. Plumb it in the same as the old. Its quiet and will do the job. You cannot use the original location for the old pump but it bolts up nice and clear below on the fender.
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post #18 of 23 (permalink) Old 03-30-2013, 02:30 PM
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Originally Posted by pdx280 View Post
It's been shown that the heater passages should be blocked if the heater core is not in-line, not connected together as a bypass. The bypass lets coolant that would normally travel through the head go straight back to the water pump, reducing flow through the head, especially the rear cylinders. Tony D actually did some work and took measurements to show this (search Tony D and heater core bypass and you might find it, I think he posted results on this forum). Blocking the passages forces the coolant through the head, bypassing lets it avoid the head.

I don't know if it's crucial but it could be a factor.

Also, the impellers on the old water pumps have been known to corrode away, something to check.
Looking at my words here, they're not quite right. Bypassing the heater core doesn't actually bypass the head, it just allows more coolant to pass through the back-bottom portion of the head, instead of flowing evenly through the head cooling channels and up to the thermostat. Changes the flow rates and paths through the head. Just to be literally correct, for any future readers.
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post #19 of 23 (permalink) Old 04-07-2013, 03:35 PM
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how to check heater core valve

Re: the water **** valve.
Car is 1979 base model five speed.
Water **** is manual, no vacuum lines attached to it. It does have copper wire that goes to a copper coil temperature sensor under the heating unit.

While in my hand it seems that the valve lets air flow pass in either direction when the actuator is in both the extreme open and closed positions. Yes, that means I'm blowing on one tube and attempting to observe outflow on the other end.

Q1: Should this valve pass water (air in my manual test) in both the "open" position and the closed position?

I see no water passing through the main seal (as Palladin has written up) when I tested it with a garden hose while it was still installed in the car.

Q2: What exactly does this thing do if it doesn't seem to restrict water flow while in either position? I do see the tie-in to a vent control flap (directly above the heater coil).

I think I've read over 20 posts on water cocks aka heater core valve, plus Paladin's write up, plus TonyD's posts on the matter. FSM (AC) skims over this part.

I just don't seem to grasp what the valve's purpose in the A/C system is since I'm not seeing a total open or close.

I'm not trouble shooting any specific issue. I'm on a preventive maintenance kick before we drop the rebuilt engine back in the car. I want 100% new rubber hoses in the cooling system so I've put in the effort to get the hoses going to the heater control valve / watercock as well.

I've pulled the heater core and the heater core valve. Heading to the radiator shop tomorrow to have the gas tank cleaned and I'm taking the radiator and the heater core with me to have them inspected.
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post #20 of 23 (permalink) Old 06-09-2013, 12:25 PM Thread Starter
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Don't know how we missed this, so I apologize for the delay. There is a plunger in the tube, not shown, that blocks off the water to the heater core. I considered replacing it and the only thing that came close was those round rubber valves you find in faucet repair kits. Mine wasn't that bad so I did nothing.

But it is possible that if the plunger has deteriorated, then you will get water though even in the closed position.

The leak occurred when you moved the selector to cold, closing the valve. This pulled that plunger and expanded the round rubber washer type seal. Over time, it split right in the center. When it was pulled, it allowed water out of the system onto the floor.

The replacement are a much better design. Not too long ago they were available thru Nissan for about $30, though that one now is on ebay for $128.

They claim it is for AC and non AC, but I think they really mean auto air and manual air. There were only 2, count them 2, different types heater valves. This one and the one for auto air which was vacuum operated.

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