oil temp probe - how does it work?

[N74DV]

excuse the ignorant question, but how does the oil temp gauge/probe function? Upon removing my oil screen today during an oil change I was checking out the temp bulb that screws into the oil screen. Does heat transfer through the copper wire to the gauge?

I guess I'm too young cause all I've known is electric senders. :rolleyes2:

[melndav]

Re: oil temp probe - how does it work?

It's known as a bordon tube. The bulb that goes into the engine is filled with an inert gas (I sure someone here knows what it is) that expands when heated. The tube goung up to the back if the instrument is actually a very small copper capillary which allows the expanding gas inflate a bellows inside the instrument. The bellows is connected to the needle which gives you temp. without any electricity. Be very careful when you are working with the line especially where it screws into the back of the screen as the are fairly delicate and expensive to fix if fractured.

[Winston L.]

Re: oil temp probe - how does it work?

It is a thermometer so it actually has mercury in the capillary tube.

[Len Petterson]

Re: oil temp probe - how does it work?

So if you dont know you ask a ? what is legal and what is what the forum is for.
No mercury in the sensor, but a liquid or gas what expand and the gauge is acctualy a pressure gauge. A medium as a gas or liquid what is heated expands, thereby generatign pressure as everything is enclosed and the burbon tube in the gauge moves the needle in relation the temperatur. DO NOT overtighten the sensor bulb, if it leaks it is ready to be filed under G.:grumpy:
And you have to visit the local auto part store. A good one is not a lowpriced item.
To test it :Put the bulb in boiling water, the gauge should read 212 Deg F.:clue?::
Explanation: a burbone tube is a oval shaped and bent tube what have a tendency to straigthen out when pressurised. They are used in pressure gauges as indicator drivers, as they straightening they drive the neddle over a gearsegment with precisition of a watch, if you get a good one.
The airspeed indicator is also a pressure gauge but is measure so low pressure what it uses a bellow instead of a burbone tube.Never blow into the pito tube, you bust the airspeed indicator . Blowing ONTO it about 6 inches away from it will give you a reading of 30 to 40 mph.
Len

[Winston L.]

Re: oil temp probe - how does it work?

I have been present when one of those capillaries was broken and it was full of mercury. The mercury expands with increased temperature and causes the bourdon tube to move the needle exactly like a gas or liqiud.

Winston

[flyguy]

Re: oil temp probe - how does it work?

I'm just trying to remember if I still have my old one that I could cut open and see what is in it. Very interesting. I would have thought that there might be some problem with the mercury coating the inside of the tube, but that was just my first thought. Piqued my curiosity, have to check it out now. LOL.
DC

[3Dreaming]

Re: oil temp probe - how does it work?

When I broke the one on my Cub I heard the gas escape. There was no mercury. Tom

[Winston L.]

Re: oil temp probe - how does it work?

The probe I saw broken was on a Luscombe so I guess it's different. Sorry.
Tom what did you do to fix yours?

Winston

[3Dreaming]

Re: oil temp probe - how does it work?

I sent it to John Wolfe and Co., and had it repaired. Tom

[Winston L.]

Re: oil temp probe - how does it work?

I called John Wolfe to ask him about the mercury I had seen in a temp probe and he said they only made that type in England and Spain. So I doubt that the installation was original in that Luscombe.

Winston