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    M type drops about a pint of water it’s got a 10lb psi radiator cap on it is this the right one. Not had the motor long it’s had an engine rebuild about a thousand miles ago.  Anybody got any advice.  Thanks.


    Hello Samuel, The standard cap that should be on your M should be a 4Ib cap. Having said that I have a 7Ib cap on my M and seems fine. As for the water loss this requires a little explanation. If you have just a radiator only and it is filled to the brim, when the engine gets hot the water will expand and be passed out via the cap overflow this is normal. The cooling system has about 41/2 gallons in it and to loose a point of water due to expansion is about right. When the engine cools down that lost water is then replaced with air back via the cap. The next time you run the engine up to temperature air will be expelled and no water. This was how the original cooling system worked. Today we have a more modern approach to our cooling systems that include expansion tanks and catch tanks. The catch tank, collects the lost water via the cap overflow and stores it. This is then siphoned back into the radiator when it cools down via the cap so the radiator always remains full. Hope this is some help to you. If there is anything that you are not sure about please ask, we are here to help.

    Kind regards Charles Gough





    Thanks for the feed back this is all new to us and a bit frightening.  We haven’t had nothing this old before.  So it wouldn’t hurt if I bought a 7lb cap and replaced the 10lb one that’s on it now.

    Thankyou very much Samuel Smith


    Hello Samuel, A 7Ib cap will be ok, use a 50/50 mix of Blue antifreeze and see how you go. By the way, our flathead engines do tend to run a little hotter than most because of its design. Your temperature gauge takes its reading from the centre of the cylinder head (where the top hose connects). I mention this because this area is also shared by two common exhaust ports just below the head. As a result, the temperature in this area can get quite high and your gauge will read accordingly. Bear this in mind when looking at the temperature gauge. Modern cars take there temperature readings from the radiator which is more a average temperature rather than a hot spot like ours. Please keep in touch and let us know how you get on with things.

    Kind regards, Charles Gough



    Charles Thanks a lot you’ve been a great help.

    I’ll try these bits and pieces and you will be the first to know the results.


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