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MG MGB GT V8 Factory Originals Technical - Water useage

I am sure this is a basic question, but....

...how much water useage is normal? per x miles, or x months?

Thanks, as ever....
Richard Saunders

Richard,
Since the V-8 has a closed cooling system with a coolant recovery tank, theoretically there should be no coolant loss over time. In the real world, due to small seepages I would expect the coolant level in the radiator to drop maybe 1/2 inch or so per month. Any more than that and I would suspect a head gasket or other problem, check your freeze plugs (engine core plugs) for corrosion. Sometimes the heater cores leak slightly as well, you know there's a problem somewhere if you catch a whiff of coolant odor every so often.

Hope this helps,
Paul Kile
Paul Kile

Mine has always 'lost' water and I couldn't really see where. Eventually I put a catch-tank under the overflow from the expansion tank and, guess what, that is where it goes. It is quite a large system and it does get very hot (hence the 15lb cap) and I have found that even though the recommended level when cold is 'half fill the expansion tank' it pushes out the 'excess' and ends up nearly empty again. My engine is quite old and coming up for a rebuild sometime (I remember saying that 50k miles ago) but I have heard the same from Roger Parker. With the catch tank it does draw the 'lost' water back in as it cools.

You might like to try a new radiator cap. When I first bought mine (car!) I noticed that after a run it would 'vomit' a little water a few moments after a good run, a new cap stopped that.

PaulH.
Paul Hunt

I notice exactly the same symptoms on my V8, the water is pushed out of the overflow as the engine warms up, but once equilibrium is reached it doesn't lose any more water.

Keep meaning to find a bigger expansion tank.....
Chris

It sounds like I need a catch tank as it sounds like I too am losing water through the expansion tank overflow (I always seem to need just enough water to take the tank up to half full). Is a catch tank a stock item? And is it easily fitted? (for a technical dimwit)?
Richard Saunders

Richard,
A catch tank should be easy to install, you need a small (~1pint) plastic bottle with either a connection through the lid or a nipple on the bottom. The secret is that you need the connection to either enter at the bottom of the bottle or a dip tube that goes all the way to the bottom (like the pickup tube in a spray bottle). Connect the bottle to the overflow tube just under the radiator cap. The idea is that the overflow coolant will enter your catch tank, then will be sucked back into the system as it cools.

A lot of Japanese cars over here use this type of catch tank on their cooling systems, check your breaker's yards and you should be able to come up with something. I don't know why BL used the design that they did, with the pressurized catch tank. With the BL design, you still end up with an overflow. They should have put the pressure cap on the radiator and then used a non-pressurized catch tank like the one I described. With the BL design, you need a catch tank for the catch tank!

Cheers,
Paul Kile
Paul Kile

I am not sure why they went for the pressurised tank, perhaps it is because there is no room for the radiator cap with the rad so far forward.

I think it is just a question of volume - the same tank works fine with the iron 4 cylinder engine but the V8, with an increased water capacity just needs a bigger tank.
Chris

I've done pretty much as Paul K suggests - I happened to have ("If you haven't found a use for something yet you haven't kept it long enough") a plastic bottle that neatly wedges between the RHS horn, the inner wing and the front of the radiator diaphragm. I use the standard overflow hose curled round the neck of the expansion tank, through a very handy notch at the top of the radiator diaphragm under the bonnet rain channel and into the bottle. The length is just right to reach the bottom of the bottle. The only thing you have to be aware of is that removing the rad cap while the engine still has some warmth in it will loose the suction and you will have to tip the catch tank contents back into the rad. No big deal though.

Same as Chris, my 73 roadster has no expansion or catch tank but doesn't lose any water, in fact I find I can remove the rad cap without problems immediately after a run, something I would NEVER attempt with the V8.

PaulH.
Paul Hunt

The priciple of the standard overflow tank was to allow for expansion of coolant so it could be retained within the overall system and returned into the main system automatically when the engine cooled. The problem is that the tank doesn't have enough capacity so you have the situation decribed here with a catch tank for the expansion tank. I have used a larger pressurised tank for what I can't remember, but I had to double the length of the mounting strap, and the result has been no need for any top ups.

Rog
Roger Parker

This thread was discussed between 07/03/2000 and 10/03/2000

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