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MG MGB GT V8 Factory Originals Technical - Not enough heat

Now that it is getting cooler I need to use the heater and the defroster but it just does't have the heat it did when I had the four cylinder in it. There is a new heater control valve installed on the 3.5 Liter V8 and this is open.
Has anybody had a problem with the water pumps by- pass being to large and not permitting the water to be forced though the heater core? (I have flushed the core) And I have a 180 degree thermostat also! Any ideas would be helpful.
Leroy Cook

It's not uncommon and may need a revision to your plumbing - my guess is that there is not enough pressure differential from the input to the output.

Tha factory arrangement provides plenty of heat. have a look at the manual.

If you can not rearrange the supply - consider one of those high temp circulating pumps - many cars - Volvo amongst them use a pump to cool the engine after it has been switched off. You just need to find some space.
Roger

I have a factory manifold on my V8 and the heat in the cabin is great - what manifold do you have?
Chris at Octarine Services

On the factory car the thermostat bypass pipe is about the same bore as the heater pipes. The heater is longer and has the resistance of the matrix but I get about 140 degrees out of mine on a 40 degree day. My stat bypass was blocked but even when I cleared it the heater gives about the same output as before, stat open or shut, so the pump must have enough pressure to force coolant through all the passages. You do have a stat or restrictor I presume? It is possible that without either the flow through where the stat should be is that muvh bigger and easier bleeding flow away from the heater. There are many things that can affect the performance of the heater: valve not opening wide enough (non-OE valves can be incorrectly assembled so that the main valve does not open enough), blocked water passage (reverse flush heater core until clean), air passages in matrix blocked with leaf crumb, heater flap nor operating correctly or felt strip blocking the flow, fan motor connected the wrong way round (try both and see which is best).
Paul Hunt

It's not simply that the air ducting has come away?
Or do you still have a control box below the heater?. I had to remove mine (and substitute mark one foot well flaps) as I set the motor (and bellhousing) about 2-3 inches further back and had to dress up under the heater (and went a bit too far).
Peter

Which way round should hoses to heater go (valve to bottom or top of heater)/

Paul
Paul

Paul,
Heater supply (from the valve) should always plumb to the bottom of the heater matrix - this promotes natural deaeration of the system. It follows that the heater return to the water pump is the top port.
Graham Creswick

Thanks Graham,

Its just that it is other way round in Roger Williams book.

Paul
Paul

I am an new owner of factory MGBGT V8. I am getting little warmth from the heater on these cold days. I appreciate that the heater matrix could be blocked or the valve taking hot water from the block could be clogged. However the water temperature is usually on the cold side of normal which will not help.
To warm the cabin any recommendations welcome.
Iain Hallifax

Currently my V8 temp gauge rises to about 1/4" below N in a couple of miles after starting from cold, but once it reaches there the air coming from the heater is at about 140F. If you can't hold your hand on the radiator header tank (careful, it should be HOT!) when the gauge has stabilised then the coolant is probably hot enough and the problem is one of restricted water or air flow as previously discussed. Is the heater any hotter once the fans have cut in? I would doubt it, but if it is I would suspect a stuck open or missing stat. You can check for this by feeling the rad header tank as the car warms up from cold. As the temp gauge rises the header tank should only get slightly warm, but as the needle get close to or reaches N it should stop moving and the rad should suddenly get hotter, that is the stat opening as it should. If the rad warms gradually the stat is your problem, some people take them out in the mistaken belief it will help summer cooling. It won't, and it can make things worse unless a restrictor is fitted in place of the stat. Without the stat or restrictor the coolant flows too quickly, causing turbulence and local hot-spots which can cause localised boing and overheating even though the gauge may show N.
Paul Hunt

This thread was discussed between 11/11/2003 and 15/11/2003

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