I have worked out a ‘plan’ to get over the Boyce-Motometer problem, what do you think of this? Get a garden thermometer from Wilko @ 75 pence it looks just the job but too long. Grind a mark with an oilstone at the length required ( I think 3 ½”), snap the glass. Insert the thermometer into a tin lid using a rubber grommet. Boil up and watch the red stuff leak out, when you have a good boil going plug the end with araldite or similar when the red has stopped coming out. Hopefully the red will go back down when cool. That was plan’A’. Got home with the thermometer and removed it from the plastic bit, boiled up some water to see how far it would go up, put the thermometer in, the red shot straight to the top and blew the end off !!!. So plan ‘B’ is to spend another 75 pence and cut the top off first and gradually bring to the boil this time. Will it work? Is the theory correct? Will report back on progress. Beware red stuff makes an awful mess!

Blimey !!!!!!

Ian - as requested elsewhere, 'cos I get emails to you rejected, please contact me with your current address. May be able to help you with the thermometers but would prefer to first confer with you direct. Chers, Bill

Have done so Bill

Doesnt there have to be a vacuum in the thermometer?

Yes there does need to be a vacuum, but if the end is sealed up whilst the red stuff is at the end of the tube, there will be no air in there and therefore a vacuum will exist when it cools down and shrinks back. Not quite true as the pressure can never be less than the vapour pressure of the liquid but near enough for our purpose.

However......

The fluid in a normal air thermomter is usually ethanol with a rather potent red dye (the dye has to be a dense colour to be visible in such a thin bore tube) and ethanol has a boiling point of about 78 deg centigrade, rather lower in a vacuum, so sorry but this is never going to work if you want to measure engine temp.

Mercury is usually used (used to be used) for temperatures in this range but tends to be frowned upon now due to its toxicity - heavy metals and all that. There are weird concoctions used now - dont ask me what they are, I havn't a clue - which can be coloured red.

Was the original thermometer red? I never had one so not familiar with it.

Martin

Thanks Martin, Looks like I am on a loser with this one,still it was worth a try.The originals are red.The one that exploded on me was red,stunk,and the red was really hard to get off the inside of the mug I had it in! I was dead lucky that it missed the carpet!!!Her indoors would be VERY unhappy and would have cost me a lot of 'Brownie points'and I didnt have many to spare this week!!!

is it really worth the effort, I have a repro/new Boyce Motormetor on my car, when fitted square I can read it ok from the drivers seat. I do admit however that my passenger can read it clearer.