M70 using a lot of water – any ideas why?

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    • #5690
      John KingJohn King

      I have a 1948 M70. It has been completely refurbished and is pretty well as original.
      It runs very well and is used every day – except in snow and ice – but seems to use a lot of water.
      If I drive say 20 miles it uses about 1.5 ltrs of water. The engine is running at around 150 deg.C and oil pressure around 20 when warm. Is this normal? Any suggestions??
      John King

    • #5691
      Tim WilsonTim Wilson

      Hi, John:

      First, you need to establish where that water is coming from/venting. It is exactly the problem l had with my M Special when l first got it, back in 2015. I was losing large volumes of water, but couldn’t determine where the egress point was.

      John Peskett id/d my rad as an early type and l was able then, to ascertain that a ball-valve at the top of the rad was missing, thus allowing water to vent, via the overflow pipe, straight to the outside as soon as pressure built up in the cooling system. That overflow pipe was well hidden : ), due to the nose cone of my car being such a close fit around the radiator. Only once l’d taken out the rad was l able to trace the outlet pipe; I had this pipe soldered up and a new, accessible overflow outlet grafted into the header which is a peculiar custom arrangement on my Special.

      I then made up a simple expansion bottle and pipe system into which pressurised overflow can spill (and siphon back, as the car cools down after a run). This seems to work well, except perhaps on the hottest of days in standstill traffic.

      So you need to ascertain where and whence your leakage point is. I assume that your head/block are not cracked. Does your car have a heater – in which case, might there be an airlock somewhere in the system?

      Best of luck, Tim.


    • #5698
      Peter LovePeter Love

      Are the water pumps leaking? Yours PL

    • #5702
      roger murray-evansroger murray-evans

      John,I presume we are talking about an M Type?Oil pressure is very average, and nothing to do with your problem.The first thing you must address is the temperature gauge if you are running at 150C.That is 1 1/2 times boiling point!Assuming the gauge is disfunctional, and that you are not continuously boiling the coolant, it would be quite normal for a radiator, having been filled to the brim, to displace 1.5L water through the overflow system as the water warms up and expands.Try not to top up the radiator before doing quite a few more miles and determine if the 1.5L is a fairly constant refill volume.If it is, then you don’t need to investigate further (or top up), apart from the gauge of course!



    • #5704
      Charles GoughCharles Gough

      Hello John, I did some work on my cooling system when rebuilding my M type. The pressure relief valve on top of the radiator was not very good and the system would not hold any pressure. This was adapted to run a hose to a header tank fitted with a 7lb radiator cap. The overflow from the header tank ( water expansion ) goes to a catch tank. My system holds about 41/2 gallons about 22 Ltrs, when full to the brim including the header tank. When up to temperature about 185/190F on the gauge and the 7lb cap releasing excess pressure ( water expansion ) It displaced approximately just over 1Ltr . When the system was left to go stone cold again, the water in the overflow tank returned to the cooling system via the 7Lb radiator cap ( water contraction ). I was using a 50/50 mix of antifreeze / water. If your cooling system does not have any form of catch tank or a properly working radiator cap any water that is expelled is lost to the ground. When you check the radiator again you will see that the level has dropped to just above the core and could be misleading ( no other leaks accepted )  do not trust the original relief valve. Hope this helps you out kind regards,



    • #5709
      John KingJohn King

      Thanks gents for your replies.  I will investigate and revert with my findings.

      John King

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