temp sender

[rutter123]

i have fitted this little number into the dash, just a digital temp gauge stripped out and adapted to fit with a little dremelling of the cluster, my question is can i use this with a standard bx temp sender in place of temp switch on the stat housing, or will i need to use the sender supplied with the unit which is the wrong size thread and will need an adaptor?

[Vanny]

Orignal sensor simply varies resistance with temperature. If the digital guage you've fitted uses a similar sensor (and it probably does) then you might be able to use the original sensor. However you'll need to know if they give the same resistance per degree of temperature change, this is pretty unlikely but possible.

To figure it out, you need to put the two sensors in a mug of water with a load of ice in it and measure the resistance between the body of the sensor and the connector on the top. This gives you resistance at an approximation of 0degC. Then do the same with a mug of room temp water to give you an idea of the temp at about 20dg. Then finally the tricky bit, you need to get a pan of water on the hob, get it to the point where it is just starting to boil (bubbles on the surface of the pan). Put the sensors in and measure again. This will give you resistance at 100dg. Not a perfect way to do it, but a very good way to see if the sensors are the same.

PS you only want the measuring head in the water really, think on the BX sensor its about 10mm long, up to the thread.

Good Luck!

[rutter123]

so for the sake of prob less than a tenner i will buy a bx sender and fingers crossed, save the messing around, i was thinking surely a sender is a sender? they are all pretty much the same thing the old school type arent they? also would it make any difference if i lengthened the sender wire as its about a foot short.

[Vanny]

You'll find they often have different ranges, given by a code on the side of the brass body. They can be easily tuned to suit a specific application by using an offset inline (internally to the sensor). I wouldn't be surprised if the measured location and the real water temp are actually different, so by tweaking what sensor is put in, you can give a more accurate idea of the actual water temp in the block / worst case.

Extending the wire shouldn't do any harm, especially if done correctly, but it will depend on the normal resistance of the 'new' sensor. If the one that comes with the guage uses a range of say 0.1 to 1 ohm, then an extension could give an offset. But i doubt that would be the case!

EDIT
I do really like the idea of having a digital read out though. Might have to consider something similar myself!

[mat_fenwick]

You may be able to tweak the total resistance the display sees with a combination of resistors in series and parallel with the sender. The other point to consider is that sometimes the senders use a number of temperature sensitive resistors in the housing, to give a degree (ha!) of non linearity in the read out - i.e. a 10 degree change in the middle of the scale gives more movement than a 10 degree change when the engine is cold. Or you could simply buy and adaptor for a few quid to fit the new sender.

All that said though, you're interested in changes in the temperature rather than accuracy, so I'd just try it and see. Even if the display is obviously wrong, it'll still give you information about when the temperature is different from normal.

[rutter123]

prob more hassle than its worth, having to completely dismantle the binnacle, and cut away part of the internal plastics. finding a power supply etc, dont even know if it will work yet.

[rutter123]

thread sizes, anyone know these thread sizes as i may have to get an adaptor, on the left is a stock bx temp switch, on the right is the sender supplied with the digital unit.

[barry badger]

It might be possible to drill the centre out of the bx sender and tap it so it can be used as your adaptor. The one on the right might be bsp, there's one taper pipe tap that comes in the metric snap-on tap and die set. I have one, it may be the right size.

[electrokid]

to give a degree (ha!) of non linearity

Oh dear

If you take the sensor that came with the digital thermometer and dunk it in boiling water with an ohmeter attached then you'll get some idea of the resistance that is needed. The correct sensor for the BX (which normally fits at the back on the engine - not at the 2 sensors for THE LAMPS OF DEATH which you seem to have replaced with the digital display) should read 130 ohms at 100 degrees C but if you buy the official part I think it reads about 10 degrees out. That might be so that the normal gauge reads 100 when it's about to boil (whereas us bright people know that a pressurised system with an antifreeze mix boils at closer to 110 degrees C).

The sensors for THE LAMPS OF DEATH are a different thread to the normal temp gauge sensor - check to see if the sensor you've been supplied with the digital gauge actually fits in the normal place at the back of the engine.

If you don't have an ohmeter then hook up the sensor you need to test to the digital gauge.

[rutter123]

i didnt know diesels were fitted with a sensor at the back of the engine as it has no temp gauge fitted so why would it have a sensor? i have never seen one on any of my diesels but on the contrary have never looked for it. maybe there is a blanking plug in place of this?

[mat_fenwick]

The new sender is probably 1/8" NPTF; the BX one is M12 x 1.25 mm. This should do the trick.

[rutter123]

have today fitted a temp sender (interpart 52220 from pug 205/405 t/d) £4.90 and on the shelf at my local factors, in place of the 110 degree c switch, seems to do the job ok generally giving a reading of between 66 and 75 deg which i would guess is not too far out, certainly accurate enough to notice any sudden change in temp. i have still kept the yellow lamp of death early warning your head gasket has gone but will be looking for a lower temp switch maybe 90 degrees to put in its place as a secondary safety measure.

[electrokid]

i have still kept the yellow lamp of death early warning your head gasket has gone but will be looking for a lower temp switch maybe 90 degrees to put in its place as a secondary safety measure.

That's a good idea - the original switches operate at temperatures that are so high - if you drive for more than 5 minutes without noticing one of the lamps is on the head is fubar.

If you find such a switch I'm sure it would be appreciated if you post the details here

[rutter123]

im sure i see one somewhere on the web 90 degree switch same fitment RENAULT?? rings a bell, will have a look and post up if any joy, i agree with what you say about the temp switches i think early warning at 100 degree c is far too late, at least with a 90 hooked up to a separate warning light (i wouldnt trust the dash bulbs) you may buy a little more time before meltdown. prime example last week my 19 year old niece on her way to work in her 57 plate corsa 1.3cdti low water warning light came on by the time she pulled up the engine was cooked fubar. 57k on the clock, when she called me in tears on the hard shoulder i asked if she looked at the temp gauge, and her reply "what temp gauge?" none fitted on these cars.

[rutter123]

just had a quick look on ebay there are plenty of lower temp switches that will fit, the thread is m14 x 1.25 (on a diesel) and prob best option is a radiator fan switch as these switch at about 86-92 degrees c, these are available as single and two pin and cant see any reason why they wouldnt do the job. you can test them first by bringing them to the boil in the kettle, but dont tell the wife. i would just remove the old switch first and check you have the depth in the stat housing to accept the longer probe in some cases.