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why no heat?

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why no heat?
  This topic is about my 1966 MG MGB GT
sweetfred Avatar
sweetfred Fredrik Nilsson
Malmö, Skåne, Sweden   SWE
Hi folks
I have no heat in my -66. It all seems ok: heater contol valve (i boild and checked), fans blow cold air.
I may have some goo inte system but I have flushed it back and forth some time ago...
What is wrong?

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lewisrn Avatar
lewisrn Gold Member Bob L
Danville, IN, USA   USA
1980 MG MGB "The "B"
Have you made sure that coolant is passing into and out of the heater core?

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bev sleet Avatar
bev sleet Bev S
Raunds, Northamptonshire, UK   GBR
Thermostat no good or air lock in the system

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course2kid Jeffrey Johnson
Fountain Valley, CA, USA   USA
1979 MG MGB "Lucy (Lucifer)"
Since your fan is functioning, all that you are missing is hot coolant flowing through the heater core. If the car runs fine without overheating, then the water pump must be circulating coolant. So, if you're not getting coolant flow through the heater core, either the heater valve isn't open, the valve is clogged, the heater core is clogged up, or the engine block coolant passage to the heater valve is plugged up.

I'd first check the adjustment of the cable to the heater core valve to make sure it is open. If that is OK, then you could pull the hoses off the heater core and blow through it to be sure it isn't clogged. Next, you could remove the heater valve and verify it isn't clogged. And lastly, you could start the engine with the heater valve removed to verify coolant gets pumped out of the block.

You could also check the thermostat for being stuck closed, the radiator (to be sure it isn't clogged), and the water pump, but, if the car runs without overheating, these three are presumably all working OK.

Edited 2 time(s). Last edit at 2017-12-03 01:33 PM by course2kid.

ozieagle Avatar
ozieagle Gold Member Herb Adler
Geelong Victoria, Australia   AUS
1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"
The simplest first test would be to feel the heater hoses to see if they are hot, once the engine has warmed up. If they are hot, then you need to check the heater, like is the flap that controls the air flow actually moving.

Also check out this extract, from Paul Hunt's website.


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Alpha-1 Avatar
Alpha-1 Silver Member Len Geiger
Jacksonville, FL, USA   USA
1973 MG MGB "Blaze"
1995 GMC Yukon "Bonnie Blue" much heat were you expecting?

‘73 Blaze Red roadster. ANSA exhaust. Rick Ingram struts front & rear, Weber 32/36, Schlemmerized 1974 Lucas 25D points distributor with Pertronics Flame Thrower coil, Minator alloy wheels, I prefer Levi’s 514.

My MGB is like a former girlfriend:
Beautiful on the outside, a little broken on the inside...
...often topless

DrewM Avatar
DrewM Silver Member Drew Maddock
74 MGB roadster, Southern California, USA   USA
Fredrik, you've got the opposite problem of mine! I've got a thread about "too much" heat in my '74 roadster. I've got defroster heat I don't want. And I've got hot air coming into the passenger compartment I don't need. In Southern California, you don't need a lot of heat in an MGB. Maybe we should trade cars?! cool smiley

The suggestions above are all excellent. Yes, check the hot water hose to the heater box. I think it's the lower hose on the passenger side. If it's hot when the car is warmed up, then presumably there's no problem with the heater valve or engine, but instead a problem inside the heater box. Apparently, there's a flap or door in the heater box that has to open to let heat into the car. It's moved by the heat-defrost heater knob. Maybe that flap / door is stuck closed? Removing the heater box should be your last resort, though so consider all the other suggestions first.

Also maybe install seat heaters? Or buy a heated blanket? Moss Motors sells them. thumbs up

You may find some useful information in my thread:,3638105

Drew Maddock, So. Calif. USofA

Edited 1 time(s). Last edit at 2017-12-03 07:17 PM by DrewM.

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CMCon98 Colin C
Dedham, MA, USA   USA
Have you considered that British sports car heaters are about equivalent to an old English lady blowing into the footwell? But seriously, there should be at least some heat coming out. It could be that a flar door in your heater box isn't moving and thus you're blowing outside fresh air into the car rather than air routed through the heater core. If you have good flow through the heater valve (make sure the block isn't clogged with rust where the heater valve bolts on) and heater core, I'd suspect air in the system or a stuck flap.

BH Davis Avatar
Thompson, CT, USA   USA
1973 MG MGB
The heater in my 73B roadster works great. It's good down to at least 20° outside.

My money on the problem is a plugged heater valve where it mounts to the block. There have been many photos posted here showing the valve mount hole completely plugged. Checking for hot heater hoses is an excellent idea. If not hot you know where to start looking.......valve or plugged heater core. Again though I'd suspect the valve mounting surface water hole.


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Steve64B Avatar
Steve64B Steve Opitz
Phoenix, AZ, USA   USA
1966 MG MGB
Fredrik, once the car is warmed up, touch the hose going from the side head to the heater core. If it's cool to the touch the problem is in the area where the valve attaches to the head. Often this area becomes blocked up with sediment, if it's blocked then there is no flow through the heater core. The solution is to take off the valve and dig out the junk causing the blockage.

sweetfred Avatar
sweetfred Fredrik Nilsson
Malmö, Skåne, Sweden   SWE
Thanks everyone! Have flushed it all and will check accordingly, when I get the engine back in.

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