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1986 Unimog U1700L (435 series)
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Discussion Starter #1
Just tried to fit up an oil temperature sensor to the oil filter drain plug. Its M10x1mm. Its not tapered and I fitted with copper washer and thread tape. Fitted well, but I tightened to what I thought was enough to stop an oil leak but it sheared off. As its a thin hollow tube, then torque is less than a normal brass bolt. No details came with it. Some sites suggest for 8Nm to 18Nm. All over the place. Does anyone have an idea what sort of torque I should be looking at. I don't expect the exact value, just that I don't have a feel for what sort of value to use on a thin hollow brass tube.
 

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I would not go above 20Nm for sure. The big issue is getting a good seal and with the type of copper washers we normally have on oil plugs, you need a fair bit of torque - maybe a fibre washer is better or a bit of Loctite PTFE paste.
 

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Discussion Starter #3
Thanks Krietpiel. I'll give a fibre washer a go, with thread lock.
 

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1988 U1300L RW1 Working gears Dual Tanks AC Rigged for Camping Plus: 91 F250 HD 4x4
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Jason, based on my recent experience, you have got off on the wrong foot here. Parallel threaded fluid fittings, such as your sensor, DO NOT seal the sensor threads to the female threads of the fitting you are installing into. Do not use sealant tape, although you might use anti-seize on the male threads before inserting (the danger of gooping the female fitting is that the goop is pushed forward in a glob that might cover the input port of the sensor).

The seal is created by the washer that you place under the head of the sensor, and presupposes that this sensor is screwing down onto a flat machined surface: you are sealing between sensor face and female fitting, face ONLY. I say this in case you are inserting into one leg of a cast Tee fitting: it would likely be too irregular a surface to seal properly. Manifolds with a machined face are the best receptor for these sensors.

I am currently deeply involved with a sensor-dependent industrial project. I started with 1/4" NPT threaded sensors, but sealing of these tapered threads is touchy and problematic. On my Mog, some time back I had pulled an M20 x 1 (?) air line test port out of the 4-way valve, and installed an M20 Male x 3/8" MPT adapter. Parker-Hannifin set me up with a washered O-ring to seal the M20, to replace the steel washer under the M20 test port (all for 300psi, mind you). The integral steel washer bonded to and surrounding the O-ring sets a crush limit for the O-ring, and prevents it from extruding outwards away from the threads, due to rotation/ advancing of the fitting face. These washers are used in hydraulic fittings, at thousands of psi pressures: because everything is steel, high torques are no problem. Picture shows the removed fitting and steel washer, and on the right is the replacement O-ring washer used for the new fitting. It has held fine for 1 1/2 years now.
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If you have a good hydraulic hose and fitting supplier within reach, I expect they could set you up; the ID should match the M10.

In my industrial application, I have moved to a sensor with a stainless steel G1/8-27 male threaded process port, with an integral O-ring groove under the face of the sensor body. This is a parallel thread metric standard, and very close in diameter to your M10. You should check your sensor, if it has the groove cut in the face, you just use a plain O-ring (NOT the washered type). Meanwhile, my supplier specifies a torque of 20-25 NM (15-18 ft-lbs), which is not very much, and this is for a SS body. I would go no higher than 20 NM on your brass fitting. By way of comparison, the spec for a 3/8" (close to M10) brass bolt is 16 ft-lbs, and specs for brass flare fittings of similar size are 17-20 NM (steel significantly higher). To finish, I believe that your copper washer is very good for high pressure steel fittings, but you will not likely be able to generate enough torque and therefore compressive force to effect a seal in your application. And, if you do not have the O-ring groove in your sensor then you really need the washered version pictured above.

Hope this helps

Lee
 

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The o-ring washers are great. As for torque, I would never use a torque wrench for a fitting like this. Just seat the washer by hand then use a wrench or socket to gently snug up the fitting. Then check for leaks. Anything more is excessive Really.
 

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Discussion Starter #7
Thanks Doka TD. Also relevant, as I am fitting the temperature sensor to the oil filter canister, there will not be a good earth connection, so I am fitting a copper eye lug on the sensor to ensure a good earth connection. I'll now likely use the eye lug as the copper washer with thread lock.
 

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Thread lock should not be required with a crushable copper washer. You can anneal your copper earth connection to insure it is crushable. Once crushed well enough the hardware should not loosen with use.
 

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1988 U1300L RW1 Working gears Dual Tanks AC Rigged for Camping Plus: 91 F250 HD 4x4
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Thanks Doka TD. Also relevant, as I am fitting the temperature sensor to the oil filter canister, there will not be a good earth connection, so I am fitting a copper eye lug on the sensor to ensure a good earth connection. I'll now likely use the eye lug as the copper washer with thread lock.
Jason, since you haven't used the O-ring washers before, I am thinking you might be missing a key point. The O-ring rubber is thicker than the steel washer. When fully seated, the O-ring squishes into more of a square cross section, creating a seal between the manifold surface and O-ring, and between the O-ring and the face of the sensor. There is no seal between male and female threads. The steel ring sets the crush depth, and prevents sideways blowout of the O-ring. For your application, this is far superior to the copper washer, which needs a lot more torque and compressive force to create a seal. See attached:

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Your reply makes me think you are going to stack a copper washer between O-ring and sensor. That will NOT seal, as it will increase the height the O-ring has to fill.

Think of the drain plugs on the portal boxes: steel bolt, copper washer, machined surface and tapped hole. You need a lot of torque to get a seal on the copper washer, and you DO NOT use any thread lock or thread seal. The O-ring does the sealing at very low torque value, just enough to not rattle loose, because of the softer rubber.

Your plan to put a temperature sensor on the oil filter canister is certainly novel. Based on my experience with this sort of sensor and O-ring I would suggest something like the following. You must have a good, machined surface facing the sensor, perpendicular to the threaded hole, or the steel washer will hit at one side only. If I were doing this, I would get a 30mm +/- diameter steel round stock, and mill the face, then drill and machine tap (to keep straight, on axis) the M10 x 1. Then cut off, grind to cope concave to fit the curve of the canister. Then drill oversize in the can and do TIG seal weld all around. For the ground, I would simply do a M6 weld nut (sand off the zinc first) nearby, on the canister, and then a ground strap with a ring connector and M6 RH MS will work fine, and detach easily if needed to change oil filters. This is a reason to NOT use goop in the threads, that is your ground path. Another reason to not use thread locker: if you have to remove, you have to clean well to re-install, and if this is your seal point, it must be really clean. Pretty much everything you do for a tapered thread seal is bad or wrong for parallel threads with O-rings.

Section of suggested weldment/ sensor

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Permatex has a product Seal + Lock Thread Compound, that I have used. It does seal tapered threads, but does not lock that securely, and as a hard-setting material, it is a devil to get off the threads when you must remove and replace. I got away from it pretty quickly.

I would definitely put in my best effort on this, as it is in a bad location to start leaking engine oil.

Having started something, figured I better make clear the issues with what I suggested.

Lee
 

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Discussion Starter #10
Thanks Lee. Lots of effort in your replies. I will certainly take this all on board.If I can solder a return connection to the body of the brass sensor without buggering it, I'll be able to use the proper O-ring washers.
 

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Thanks Lee. Lots of effort in your replies. I will certainly take this all on board.If I can solder a return connection to the body of the brass sensor without buggering it, I'll be able to use the proper O-ring washers.
Jason,
a couple years ago I had a ground issue on the oil pressure sensor on my F250. I did a sleazy fix by bringing over a ground wire, and securing to the sensor body with a hose clamp (!). If you are in fact performing surgery on the filter canister, a ground to the canister will work fine; after all, the whole truck is grounded thru steel components, with a few copper straps to jump the gaps.

And do post photos of the finished product, I am really curious how this turns out.

Lee
 

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Is your sensor not grounded by the body of the sensor? I’m lost on why this is getting so complicated.
 

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All due to the second law of thermodynamics :p
As I understand it, the

Three Laws of Thermodynamics are:

1) You can't win
2) You can't break even
3) You always lose

Not sure if 2) is the best applied, to this situation, but I'll go along, to get along.
 

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I'm thermally confused!
 

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I'm thermally confused!
But hopefully not e-thermally confused. That would be never-ending.

Now, no pressure here, but my sense is that everyone needs to chill out and not get too torqued up over this.

So, in the interest of being less serious......

There is a simple way to decide a course of action, which is to gather data. Crawled under my truck and looked at the oil filter drain plug (I had forgot the details). It sits on a nice boss on a cast canister / filter housing, which is non-ferrous, so any comment I made about welding on a fitting should be re-evaluated. However, running a continuity check between the filter housing and a randomly selected bolt on the truck frame shows 1 ohm, same from the plug itself. The filter housing is a perfectly fine ground connection. If the threads match, and the boss on the casting is at least as large as the O-ring washer, it is an excruciatingly easy fit-up. The sensor body is the ground (typical of sensors for automotive applications, whereas the industrial sensors I am using are dedicated 3-wire types), and one need only attach a single wire to the electrical contact on top of the sensor. There, that was not so bad. And remember, no thread sealant, that is the ground path.

If there is a second sensor involved somewhere, the point to watch for is parallel surfaces on sensor and receptor tapped hole.

Lee
 
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