How to replace a oil tank level sending unit?

[randywebb]

It's funny - I've had 2 911s ('75 & '73) and both have had oil level gauges that worked fine. I replaced the one on the '73 but it reads just fine now.

But, based on posts, this is one of the most failure prone parts of the 911.

Report back after you try it fully warmed up.

You can test it with an ohm meter - measure the resistance of the unit with the arm in various positions.

Sometimes a PO will get frustrated and disconnect the wires to the gauge - that happened on my '73 - worth a check.

[Chuck Jones]

I went out and fired up the car, let it idle until it was good and warm, and checked the dipstick....over the full mark. Then I checked the oil level gauge and saw that it was sitting in the red. I shut off the engine and turned the ignition and pulled off one of the wires with a spade connector fitting. I then turned on the ignition and the gauge pegged all the way to the top. I did that several times to make sure that the needle was moving freely. I hooked the wire back on and turned the ignition switch on and off several times and noticed that the gauge tried to go up, but it was stopped abruptly in the red zone by seemingly by some unseen obstacle. I could hear the gauge click like it was hitting something...yet when I pull off the wire, the needle easily moves all the way to the top of the gauge. This would seem to point to the sending unit...perhaps something in there blocking the float.....As much as I don't want to, I think I'm going to have to pull the dogone sending unit out again and fish around in the tank....it could be possible that the PO dropped something in there and it's hitting the float. If someone dropped the dipstick in there...would it hit or obstruct the float? The dipstick is still in the retaining tube, but I was wondering if perhaps there might be another on that's been dropped in there by the PO? I don't know....just looking for options.

[skipdup]

Both my SC & 930 have gauges that read/work perfectly. For once, I must be lucky.

[randywebb]

that's a reasonable next step - good luck

[Chuck Jones]

Ok...I decided to tear into it again, and checked it by first pulling off the ground wire and rechecking the gaue...it registered all the way to the top...so the gauge works fine. Then I took it out (using the methodology and orientation from the cardboard cutout explained in earlier posts) and held it next to the old one to see if the float arm was the same angle, and it was. I checked the resistance of the sending unit with a multimeter and it registered as I moved the float arm up and down, so the sending unit works. (PS..the old one checked out fine too!)

I checked inside the tank to make sure there was no obstruction in there and everything seemed in order....I did see a fine wire mesh at the back end of the tank....must be a baffle of some sort to keep the oil from sloshing.

I reinstalled the gauge...it (took about 15 seconds this time...I'm getting good at this) and hooked it up. The sending unit can only go in one way due to the offset pattern of the bolts. I fired up the engine and let it warm up. I could see the needle moving this time...so it looks like its working, but it the float arm must be set at too high of an angle, because with the dipstick reading full, the gauge barely moves off the red...even when the engine is hot after a good run.

I think the only thing left to do is bend the wire of the float arm down to lower the float and allow it to contact the surface of the oil sooner...thus providing a reading on the gauge. I haven't read of anyone doing this because the sending unit comes already calibrated from the factory, and that wire arm that holds the float is pretty stiff and hard to bend. In the end, I guess this is about as good as it gets...and I might as well leave well enough alone...use the dipstick for an accurate reading. Isn't that where I started?

[randywebb]

Hmmmm... there are 2 different p/n's for sending units. I was told they were the same but just maybe they are 'calibrated' differently.

Sounds like you've covered the bases and bending is the fix.