Temperature sender high reading

Post by **plantscience** » Fri Jan 23, 2009 4:16 pm

Wonder if anyone can help. My Morris 1000 (1958) had a temperature guage fitted by the last owner.
However, it seems to read at around 100DegC (rather than the expected 90Deg C) when run for a while. And this weather stationary at high revs (to test it) or moving. I have changed the thermostat so can discount that. Also all those issues around binding brakes etc which may cause high temperature. In fact the engine does not seem over hot when I open the bonnet and feel the water pipes (just quite warm). And even when I open the radiaotr cap... Carefully... It is not boiling. (Also, new radiator and pipes and flushed out the system)

So I am wondering if there might be a fault with the temperature sender. Is this likely?

I read that some guages (and this is a 'Smith' guage) need a voltage regulator to step down to 10v. Could this be the problem? Higher than required voltage if no regulator present? So higher than actual reading?

Can anyone help please as I have run out of ideas!!

Thanks

Post by **bmcecosse** » Fri Jan 23, 2009 4:21 pm

Yes - if it's an electric gAUge - it needs 10 volts. Happily - if your car has the 'slow moving' fuel gauge - it also needs 10 volts and there will be a little regulator in beside the speedo. However - I suspect 58 car has fast fuel gauge - so you will need to source a 10 volt regulator from a later speedo - or get something suitable in Maplins.

Post by **PSL184** » Fri Jan 23, 2009 4:22 pm

Your last sentence is indeed the problem "IF" you are feeding the gauge with 12 volts. They are designed to run on 10 volts and will read high if not correct. Simple to fix. Just obtain a voltage reg from a scrapped Mini or later Minor and wire the gauge feed through it. The reg body needs to be earthed so just screw it somewhere convienient behind the glovebox....

Post by **plantscience** » Fri Jan 23, 2009 6:40 pm

Thanks to you both. Good of you to help.
Much appreciated. I will nip down to maplins tomorrow and see if they have a regulator. I guess I just need to ask for a unit that will step down 12v to 10v and connect in line witht he temperature guage. I suppose this is not the wire from teh temperature sensor itself but the 'other' one?

Post by **PSL184** » Fri Jan 23, 2009 6:53 pm

Correct - The wire from the sensor is the earth - the other one supplies the voltage...

Post by **plantscience** » Fri Jan 23, 2009 8:14 pm

Thanks PSL. Will let you know how I get on...

Post by **IslipMinor** » Mon Jan 26, 2009 10:06 pm

This is the one that I seen suggetsed before, but have not tried it.

Maplin Product Number: N38CA (1A positive)

http://www.maplin.co.uk/Module.aspx?ModuleNo=46475

They are only available in 10v POSITIVE, i.e. for negative earth cars only.

Be interested how you get on?

Post by **PSL184** » Mon Jan 26, 2009 10:55 pm

Interesting to note that the modern ones are polarity sensitive - The original type fitted to Minis and later Minors don't seem to care which way round the earth is.....

Post by **bmcecosse** » Tue Jan 27, 2009 12:47 pm

Because they are simple bi-metal strip type - they switch on/off as the bimetal heats and cools - giving an 'average' output of ~10 volts, but in fact it varies from 14 volts to zero! So - they are only suitable for 'hot wire' instruments - where they operate by current flow which depends on the resistance of the sender unit.