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MG MGB Technical - Direction of Coolant flow?

Paul Hunt's wonderful website refers to the "coolant return pipe" laying along the top of the tappet cover. I'm half-way through r and r of heater box in order to put in a new matrix; all has gone smoothly in respect of removal of heater box, strip and paint in readiness for new matrix - and I originally thought the flow of coolant would be from the "up" side, powered by the water pump, down through the matrix and out of the lower pipe and on to the valve which governed whether flow was allowed or not. But that would make the pipe atop the tappet cover the "supply" pipe, so have I got it wrong?? Is the flow governed FIRST by the heater valve, then drawn upwards through the matrix by the water pump and out of the top pipe? I'm confused - and it makes a difference to where and why my old matrix developed a leak. All help gratefully received - I don't have a direct contact for Paul Hunt. Regards, John.
J P Hall

The water flow is out of the radiator at the bottom with the help of the water pump draw, up through the block past the thermostat into the top tank. This means the hottest part is the cylinder head so the heater supply is there. Also the water pump lowers the pressure in the lower hose helping the flow through the return pipe. At the same time the syphon effect of the hot water rising in the block and cooler water falling in the radiator keeps it all going. Denis

In the past I have measured the temperature of the heater valve at 71C and the return pipe at 65C, so I am confident it does flow that way in practice, although as I have found in domestic heating systems turbulence can cause the flow to be in the reverse direction to that expected.

As Denis says the flow is governed by the pump, which simultaneously pulls coolant from the bottom of the rad and pushes it into the bottom of the block, where it flows up through the block and head, and from there into the top of the radiator. The heater matrix is effectively another radiator, which is why the flow to it is from the head just like the main radiator, and the return from it goes into the bottom hose. When the thermostat is closed during warm-up the pump forces coolant from the head to flow through the heater matrix and back to the pump via the return hose, as well as a bypass port in the head allowing cooling to flow from the head back into the pump.

Hadn't noticed my email wasn't being shown, it should be now, but there is also an email link on the website. Thank you for the kind words, by the way.
Paul Hunt

Incidentally I also meant to say that direction of flow should not have any effect on where and why a leak developed in the matrix. The resistance of the matrix to flow is minimal so the pressure will be relatively equal throughout. The leak will have occurred where the weakest point was.
Paul Hunt

Another often overlooked, and little understood function of the cooling system is the radiator cap itself. When the cap is removed and the engine is running, cavitation, or air bubbles, form at the entrance to the inlet of the water pump. With no radiator cap installed or one that isn't holding pressure, there is a %20 drop in cooling system efficiency. RAY
rjm RAY

Thanks all - I'm the wiser for your input. The plot thickens, because in fact when I submerged the tank and fed air through one pipe with the other blocked, no air bubbles could be seen. This is despite evidence of long term water sitting on the matrix ends and in the heater box. So it looks as though, as Paul states in his detailed notes, my problem might have been water escaping from hose clamp areas and gathering where gravity dictated - over a period of years, undetected. I'm going to fit the new matrix anyway, as it's on its way from the UK; and probably double-clamp at hose ends. In case it's of interest, I'll post the final outcome. I'm off today for a shoulder reconstruction, so it won't be for a week or two! Regards, John.
J P Hall

John, if it's anything like what I went through, your shoulder reconstruction should go without a hitch. I had mine done, a year and a half ago, at Stanford University Hospital in Redwood City, CA. It took less than three hours and I stopped taking the pain medication the very next day. Recovery was complete in less than six months. I can't believe the difference that it's made in my life. I was fortunate enough to have the work done by one of the staff professors. I hope everything works out for the best and here's to a speedy recovery. RAY
rjm RAY

Thank you Ray - I'm just back home and feeling very sore; only micro-movements possible at the moment, but your words give me encouragement. As you might notice from a new thread today, I've managed to sneak into the garage and check the engine number and ask for more help on the BBS! Regards, John.
J P Hall

Just out of interest, what did you end up having done to your shoulder----------I'm interested in the outcome/ recovery
William Revit

Hi Willy - the original diagnosis from MRI was a Supra Labral Anterior/Posterior Tear ( a "SLAP" Tear). When I saw the orthopaedic surgeon (a fellow hockey player but at 52,10 years my junior) he said something about possibly reattaching one of the two biceps tendons to the bone, and something about a sub-acromial repair. I was none the wiser. After the op. last Thursday, he visited me while I was still half-sedated and I THINK he said he cleaned out detritus which was causing biceps tendon to impinge on nerve somewhere; also using a dremel(!) to remove bone at the same point of impingement; nothing said about sub-acromion or SLAP tear, so I'll remain confused until I see him in a week's time. My overall impression is that the MRI was "indicative" at best, and that only when the surgeon "goes in" can he really see what needs doing. As to recovery, you'd better not ask me yet, as all I can feel is more pain than before, at the original sites of pain! Kind regards, John.
J P Hall

John, I hope that you heal quickly, with minimal pain. However, don't push your luck trying to do things that you shouldn't or you will be back to square one. This was made very clear to me by my doctor. I heeded his advice and am very glad that I did. RAY
rjm RAY

Very sound advice Ray, thank you. I'm definitely on light duties for the next couple of weeks - just a bit of sandblasting and priming of parts today; how good is this hobby that we can find things to do any time, night or day! Regards, John.
J P Hall

This thread was discussed between 06/01/2016 and 12/01/2016

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