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  • thedawnpatrol
    Rank 5 Registered User
    • Oct 2009
    • 611

    RR Merlin Thermostat Question

    before I endeavour to strip and rebuild my Hurricane Thermostat, does anyone have any advice or experience with getting these to work, or indeed know of any new old stock availability ?

  • Vintage
    Rank 3 Registered User
    • Aug 2018
    • 46

    #2
    Have you asked BBMF? Cheers

    V

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    • Beaufighter VI
      Rank 5 Registered User
      • Sep 2005
      • 519

      #3
      Spitfire Modification 1323 issued in 1946 deleted these thermostats on Merlin & Griffon engines with two piece cylinder blocks.

      If you still want to try to get one functioning I can help with NOS and Teddington manual.
      " I'm not young enough to know everything." - J M Barrie 1903

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      • thedawnpatrol
        Rank 5 Registered User
        • Oct 2009
        • 611

        #4
        thanks Beaufighter, that's interesting as my Hurricane was fitted with a Packard Merlin 29, (two piece block) but still had this thermostat fitted to the airframe, i guess the aircraft was obsolete before the 1946 mod date.
        so i'm now wondering how many, if any of the present warbirds fly with them ? taking into account that most have two piece blocks. ?

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        • powerandpassion
          Never Be Afraid to Ask
          • Jul 2012
          • 1237

          #5
          BeaufighterVI, very interesting about the 1946 mod - what is the logic behind it ? I assume this is also for two stage supercharging? In this case keeping the engine colder for longer aids in managing pre ignition of boosted, high temperature, high octane fuels? Is it possible to post the mod or explain the logic behind it.

          I would be interested in NOS or tech info on how to refurbish these thermostats, after the redback spiders have been shaken out. Happy to pay for a copy. Certainly in two stage Packard build Merlin 69s used in postwar RAAF Mosquito PR41 the thermostats continued to be used. These same engines, rebadged as V3 -V7s were used in CAC Mustang, not sure if they had thermostats fitted. Can't tell you f Griffon powered Fairey Fireflies had 'em either.

          I guess the application in PR41 was lean running, long distance flight, rather than short, sharp climb to height of a UK based Spitfire. Did the 1946 mod incorporate the use of heated oil pumped into the engine?

          Another aspect of these cooling systems looked into postwar was electrolytic corrosion set up between aluminium engine and copper based pipework, header tanks, radiators, solders etc, with materials like tungum thrown in the mix that may have shortened engine life. Not such an issue during conflict, more of an issue with postwar Transport Merlins.

          I think today there is a good argument for the fixing of sacrificial anodes in the cooling system to assist in the long term integrity of aluminium based engines operated for intermittent, short periods but expected to be in service for decades. This is an unremarkable thing for marine racing engines using seawater-freshwater cooling systems made of various metals. In the case of Merlins the sacrificial material would have to be magnesium. Most interesting that in 1935 , based on remains pulled from under a chook shed, RR50 Kestrel engined Hawker Hinds were fitted with cast magnesium coolant pipe elbows, in an accessible place for replacement. I can only think that there was some recognition of the value of extending engine life this way in 1935, lost in the fury and urgency of the war.

          Comment

          • QldSpitty
            Rank 5 Registered User
            • Apr 2006
            • 2604

            #6
            AvspecsFrom Avspecs quite a few years ago now during the restoration of BL628
            Attached Files
            "If the C.O. ask's you to be Tail End Charlie...just shoot him!!!....A Piece of Cake.
            http://spitfirea58-27.blogspot.com.au/

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            • powerandpassion
              Never Be Afraid to Ask
              • Jul 2012
              • 1237

              #7
              Never drink soup offered by a Kiwi...

              Comment

              • MerlinPete
                Rank 5 Registered User
                • Jan 2006
                • 1274

                #8
                As far as I understand it, whether the thermostat is fitted or not has little to do with coolant temperature, the radiator shutters do the same job, but conversely, I don`t know therefore why thermostats were used at all? Later installations on Lancasters tend not to have them, neither does the Shack.
                If I had a quid for every time someone mentioned "buried crated Merlins", I could buy one!

                www.flightengineering.co.uk

                Comment

                • Beaufighter VI
                  Rank 5 Registered User
                  • Sep 2005
                  • 519

                  #9
                  The thermostat aided a quick warm up by allowing coolant to bypass the radiator up to a specified temperature. This would reduce the temperature difference between head and skirt/liner which would give uneven expansion and distortion. This would be relevant too once piece cylinder blocks and narrow flange blocks.
                  Of course it would also allow a quicker warm up and shorten time to take off.
                  " I'm not young enough to know everything." - J M Barrie 1903

                  Comment

                  • Vintage
                    Rank 3 Registered User
                    • Aug 2018
                    • 46

                    #10
                    Hmmm, There is no doubt that a thermostat on liquid cooled engines is generally used to give shortest warm-up and minimise the time that the engine is running with low coolant and oil temperatures. The specific implications for the integrity of an engines construction joints and working clearances is going to be very type specific but, maybe there is detail somewhere that explains how Rolls-Royce viewed this for the incorporation of a coolant thermostat on Merlin installations? I agree that, particularly for fighter types, warm-up times can be problematic. Of course, the oil temp is often slowest to build and is perhaps the more limiting factor, oil system thermostatic control and short-circuiting for warm-up is often a feature. The importance of oil system warm-up in some applications can also be seen in the use of oil dilution with fuel for cold start. Cheers

                    V

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