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MG MGA - Why won't my @#*% heater work?

Hi all

My heater was not working very well so decided to do some investigation. After removing heater from car -

Removed the flap assembly from the front of the heater box - behind the flap is a round gauze filter. This was more than 50% clogged with dirt - cleaned this.

Removed the fan motor and stripped it down and cleaned it. The brushes looked OK. Seems to be running OK. (Should I have got a new one?)

Bought an uprated heater matrix from MGOC -this has 5 rather than 4 cores in it and more fins.

Stripped and repainted the heater box the fitted it all back together. Fitted heater box back into the car with new rubber gaskets.

Refitted the silver demister tubes from inside the car and then the demister hoses.

Refitted the cable for the air flap under the bonnet and for the air push/pull knob inside the car.

Refitted large air hose to front of heater box.

All this effort and expense was to no avail. Travelling in the car early one morning and put heater/blower on. No heat or none that you'd really notice. Temperature gauge showing 170.

So could it be that the coolant is not getting hot enough? I am thinking along the lines of trying some sort of radiator blind. Interestingly the spares manual actually shows a radiator blind (AHH5536). Anybody got one or seen one?

By the way new heater tap fitted and heater hoses are clear and are hot going in and out. Any ideas gratefully received.
p parmenter

The core of the heater may have an airlock in it. It shouldn't happen with these cars, but maybe since you have gone to another upgraded core.

.... CR
C.R. Tyrell

No mention of the heater tap or rubber hoses Phil!?
Neil MG

You don't mention the packing that should surround the heater matrix. Is that in place as it insulates the matrix to keep it hot.

Regards
Alan
AR Terry

I have a radiator blind, and only have to use it on very cold days to let the engine warm up. The heater works fine as long as the engine is hot.

The heater depends on a good flow of hot water. Are both the hoses hot when the engine is hot? Is the valve on the block gummed up and not allowing water to pass through it?

The padding inside the heater box is to make sure air goes through the matrix rather than around it. The loop of foam around the matrix is therefore important to heater operation. It has no meaningful inflation effect - in a close engine compartment everything gets pretty hot anyway.

Is the flap open - if closed you get no ram effect from air flow at the front of the car. This makes a big difference to air flow through the heater.

I also uprated the hamster wheel fan to a plastic one with bigger blades, which made a big difference when the car is not moving.
dominic clancy

Get a infrared thermometer and check the temperature profile. Befoe valve, after valve, heater inlet pipe, heater outlet pipe, thermostat housing, radiator inlet, header tank, core profile , pump return - this will isolate where your problem is. Do you have good air flow with the blower on - try disconnecting the demister tubes at the heater and closing the bottom flap then compare flow with one outlet closed (using your hands) and both open to get a feel for air flow.
Mike
Mike Ellsmore

Phil,
I would not be surprised to find that the new Heater tap does not open fully to allow full water flow. Barney has this covered on his site somewhere.

Might be worth refitting the original to check it out.

regards
Colin
Colin Manley

Got to be a water flow problem.
Art Pearse

There's an article by Bob Muenchausen in the Mike Ash NAMGAR Tech Sessions (pp277) on how he modified the heater valve by using packing washers behind the valve cup which closes off the water flow inside. By doing this he increased the heater output air temperature from 95 degF to 152 degF for the same ambient and water temperatures...............................Mike
m.j. moore

As Mike says, look at the tap on the cylinder head. I tweaked it with washers so that it only just closes when set to cold and to maximise the opening in the diaphragm when set to warm.

dan
Dan Smithers

Hi all,
Sorry - been away for a few days. Thanks for the ideas. I will follow up on them when I get the time.

Many thanks,

Phil
p parmenter

I'm thinking that, Your car temp appears normal and quite hot enough at 170deg and you say both your heater hoses are getting hot indicating good flow so heater should be hot enough
With the fan switched on are you getting a good flow of air---Maybe when you had the fan motor apart the housing might have got fitted up 1/2 a turn out which will cause the motor to spin backwards resulting in no or low air flow--If it is a two wire motor you can swap the wires over to correct this problem---If that's what's wrong ---
willy
William Revit

How do I log into this site under my own name? Not logged in leaves my post in someone else's name.


MGA heater motor is series wound an will run same direction regardless of electrical polarity. Find two black wires on the motor. mga twin cam and early MGB heater motors run opposite direction (also two black wires on the motor). Later MGB has permanent magnet field and will change rotation by switching polarity.

Check that the blower motor is actually running. The blower fan might be physically obstructed after reassembly touching the heater box shell or such.

If bower is running but air flow is cool, then there is no water flow. Installing the control lever upside down will make it work backward, so the valve might be closed when it should be open.

Remove valve from head and check for clog in the port in the head. Blow through the heater hose to be sure water will flow through the heater core. Hot water flow plus air flow equals warm air output.

~~Barney Gaylord - http://MGAguru.com
es1

es1
Sorry to go off thread but try contacting the webmaster at webmaster@mg-cars.org.uk who should be able to sort out the bug
Graham V

It seems strange that hot water is getting to the heater but not generating heat but I may have stumbled across the reason.
I have just taken my heater matrix for welding to radiator specialists as it has a small hole in it. The garage immediately said even when they fix the hole, it will not generate heat.
Sorry as I didn't fully understand the reason, but they showed me that the steel ends plates of the matrix are bulging out in a convex shape but should be flat. I had thought the convex shape was normal, but they said that will stop the matrix generating heat.
Could this be the case with yours?

Just a thought - Graham
Graham V

Hi Graham - it's a new uprated matrix so should be OK. I will investigate all this further and go over the points raised above when I get some time (bit busy at the moment)
Many thanks,
Phil
p parmenter

This thread was discussed between 02/06/2015 and 10/06/2015

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