Heater issue
09-30-2014, 10:29 AM
Post: #1
Heater issue
Right, I've had heater core problems for many years, even before I put in my 20V. but as the car hasn't been in a daily driver until now, I've never been too hassled about getting one that's not clogged until recently.

I finally got round to changing it the other day, but I'm unable to get coolant to go to it, so as a result I'm getting no heat in the cabin.

After many times trying to burp the system with the radiator sitting higher than the back of the head, it's still not getting there. I can feel that both the pipes are lukewarm at best. I'm wondering if it's my setup that's the problem, but I can't quite tell. The water relocation kit that was put on the car doesn't have lines to go to the heater, so I've had to put in 'T' junctions to circulate through it. Could anyone clarify if this the cause of the problem, or if I just need to keep burping it?

Here's a really rubbish drawing I did of a diagram showing the setup

[Image: AEU86 AE86 - Heater issue]
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09-30-2014, 08:51 PM
Post: #2
Heater issue
Very few factory systems except for something like the MR2 ever need 'burping', when their rpm gets over 2500 with the thermostat open they'll have a tremendous flow that'll push any & every bit of air to a highest & widest & lowest flowing spot in the radiator or reseviour tank.

So what!
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09-30-2014, 10:09 PM (This post was last modified: 09-30-2014 10:16 PM by jondee86.)
Post: #3
Heater issue
With the water circuit shown, the flow is essentially governed by the
resistance of the heater core versus the resistance of the radiator core.
If the resistance to flow of the heater core is greater than the resistance
of the radiator, then the water will take the path of least resistance.

AFAIK most heater pipework setups use the pressure differential created
by the water pump to ensure flow through the heater core. So I think that
you will have to tap the heater return line into the high suction zone close
to the back side of the water pump.

Cheers... jondee86
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09-30-2014, 11:14 PM
Post: #4
Heater issue
(09-30-2014 10:09 PM)jondee86 Wrote:  With the water circuit shown, the flow is essentially governed by the
resistance of the heater core versus the resistance of the radiator core.
If the resistance to flow of the heater core is greater than the resistance
of the radiator, then the water will take the path of least resistance.

AFAIK most heater pipework setups use the pressure differential created
by the water pump to ensure flow through the heater core. So I think that
you will have to tap the heater return line into the high suction zone close
to the back side of the water pump.

Cheers... jondee86

Your point about the path of least resistance is something that did cross my mind, unfortunately the water relocation kit I have doesn't allow me to set things up any other way, so I'm at a loss to figure out a way round this. Unless I can fit a T-junction right behind the water pump, which would be a tight squeeze.
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10-01-2014, 06:32 AM
Post: #5
Heater issue
To get a better pressure differential, you can either use a tapping where
there is strong suction from the pump, or a tapping where there is strong
pressure on the output side of the pump. You really need to be looking at
the whole water system (location of thermostat, high and low pressure
areas etc) to see if there is some point you can tap to get a better
differential.

Cheers... jondee86
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10-01-2014, 08:43 AM
Post: #6
Heater issue
Thanks as ever for your input jondee.

Upon reflection, upgrading my radiator to a mishimoto may have had a negative effect on the heater, as the flow through it may have had a lot less resistance compared to the old one.

To put some more perspective on the water lines on my 20v, the back of the head looks like this:

[Image: AEU86 AE86 - Heater issue]

and behind the water pump, these two points are actually connected.

[Image: AEU86 AE86 - Heater issue]

My first thought was to put a T junction directly behind the water pump leading to the core, but that would only negate the use of the thermostat. The blanking plate on the exhaust side would only do the same. My only real option with this kit would be to move the T junction on the radiator pipe so it's closer to the thermostat housing, or am I just going to end up in the same position?
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10-01-2014, 10:26 AM
Post: #7
Heater issue
Just to be clear... is your thermostat in the housing beside the pump
or in the water block at the back of the head ?

And if it is in the block at the back of the head, is it a double acting type
that blocks flow to the radiator and bypasses water directly from port to
port while cold... but blocking the bypass when fully open ?

Cheers... jondee86
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10-01-2014, 01:23 PM
Post: #8
Heater issue
The thermostat is at the back of the head and not quite as the picture shows. I don't believe it's the double action type. It just allows the coolant to flow from the head with no bypass setup.
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10-01-2014, 11:00 PM (This post was last modified: 10-01-2014 11:03 PM by jondee86.)
Post: #9
Heater issue
OK. I figure that regardless of the thermostat setup, there will have to
be a bypass somewhere inside that block, otherwise you would have no
circulation when the thermostst was closed. I will also assume that the
thermostat is blocking the return from the radiator until it starts to open.

On this basis, where the hot water exits the head can be considered a
a good place to tap for the heater flow. The blockoff plate on the side of
the head at the rear would be just as good. And where the water exits
the head and enters the pump can be considered a good place to tap for
the heater return connection. If you are using the factory alloy pipework
you should be able weld/thread/glue a 5/8" barb for a heater hose.

The heater core will basically be running in parallel with the radiator, and
will be a bypass around the thermostat when the heater valve is open.
This may delay the opening of the thermostat slightly, but given the
difference in flow rates between the heater core and the radiator, I can't
see it having any significant effect on the engine warmup.

Cheers... jondee86

PS: Looking at your drawing, if the heater flow tapping is reasonably
close to the head, then you would only need to change the return hose.
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10-02-2014, 07:51 PM
Post: #10
Heater issue
Thanks for that Jondee. I may speak with a local fabricator to see if they can make me up another blanking plate with a 5/8 barb in it. Alternatively, I may look into opting for the SQ Engineering kit to make everything neat and tidy.
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