Early XK120 oil level float

XK
#1

Hello List,

I remove my sump mounted oil level float as it was not showing actual oil levels, (always read full), and discovered that the float arm and float had detached from the oil level rheostat housing and was resting on the bottom of the oil sump. On inspection of the float the solder joint for the float arm had cracked and allowed oil to enter the float. The set screw fixing the float arm to the oil level housing had loosened allowing the float arm and float to separate from the housing.

Removing the float from the float arm a small amount of oil drained out, however, the weight of the float indicates that solidified oil crud has built up in the float. Several fills of the float with solvent have not been effective. I would like some suggestions from the group as to a more effective method and what soldering method should be used to reattach the float to the float arm so that this doesn’t reoccur.

Geoff
670203

#2

I must admit that I have never heard of a sump mounted oil level float. Is this something unique?
Pat H

#3

Hello Pat,

The oil level unit part C2349 was incorporated on all early engines that featured the studless cam covers at the front of the engine over the timing chains and was located on the right side of the sump.

Since the float lever arm is only 1/16" diameter the holes in the ends of the float are quite small and removal of the built up oil crud is difficult. I could unsolder one end of the float, remove the oil crud and reassemble the float complete with the lever arm if I new what soldering process was used on the (galvanized?) steel float.

Regards, Geoff

#4

Interesting. So, are there separate gauges for oil level and oil pressure?
Pat H

#5

My '120 has one. The fuel gauge will indicate the level of the oil in the engine by momentarily pushing a black button on the far right of the dash.

#6

I have had success with removing solidified crud by immersing the part in acetone for a week or so. Pretty much liquifies everything.

#7

Thanks Geoff. I will give it a try

#8

IF you can find toluene you can try that…the best crud cutter/degreaser I’ve ever used.

#9

Mine has it too. All 120s had it up to these engines.
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I have used both acetone and toluene and they both seem to work well.
I thought the float was brass, and the arm is steel.
Soldering technique for the float is get it really super clean with fine sandpaper, then propane torch on low flame, tin the area using flux core solder and an acid brush, then feed in some more solder. Shake off the excess; you don’t want it inside.
Same with the steel arm, get it super clean, then tin it, then feed in some solder.

Apparently Mark VII never had it. Early cars with the same aluminum sump as 120 had a blanking plate.
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One of the researchers has found that on the latest 120s the hole in the sump was not even machined, so didn’t even need the blanking plate, you’ll see a round lump there instead.

#10

The sender units for the oil level and fuel level look to be the same. If so, it could be possible to copy the float arrangement for the oil level sender and attach it to a new fuel sender (which seems to be more generally available). Does anyone know if this could be the case?

#11

Yes, the basic design is the same, but most fuel senders have two terminals, one reading the level and the other switching on a light when you are running low. The oil sender has just one terminal and just reads the level. The wire float arm would be a different length and bend configuration.

#12

If I can expand on that, cleaning is a bit of an understatement. What you are doing with the sandpaper or steel wool is removing the oxidized surface layer. The thing that makes copper, and copper alloys, corrosion resistant is not their native crystalline structure, but their proclivity to oxidize extremely rapidly at ambient temperature and pressure. That metallic oxide layer is very hard and inert (same thing goes for aluminum) and will repel soldering attempts unless it is mechanically removed. You can improve your chances for a successful solder joint by tinning the abraded surface. Easiest way to do that is with tinning paste, which is simply powdered tin combined with rosin flux. Rosin flux is a combination of organic acids. It is largely inert as a solid, but is reactive to metal oxides when heated and liquefied.

1 Like
#13

Hello Mike,

The float is definitely not copper or brass as a magnet is attracted to it when placed on it. I will thoroughly clean it and tin it as described. Thanks in advance.

Regards, Geoff

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#14

Thanks, Rob. I didn’t clock that difference. However, might it not still be possible to use a fuel sender (with appropriate arm & float) just using the terminal connected to the internal rheostat, and ignore the one for the fuel low-level light?

#15

Yes, certainly, but you would have to figure out the correct length and bends in the wire float arm. If you were clever with wiring and wanted to have a low oil warning light you could rig one up somewhere.