Dipstick and Oil level gauge not agreeing !

[Deschodt]

When I got the car (73.5T) both oil senders were shot. Since I replaced them both and changed the oil, the oil level gauge indicates full even when running at constant RPM (4000) as if I overfilled (it only goes down when I stomp on the gas - it works, it's not a short).

I refilled based on the usual method: trust the dipstick on a level, warmed up car...

Wondering if maybe the dipstick is incorrect...

Is that the correct size for a 73.5 T ? Seems short to me. If short that could make the oil level gauge correct....


PS: Who sells the tiny hex bolts that attach the seat rails to the floor ? Couldn't find them on Pelican !

[svandamme]

those hex bolts are pretty standard M8x15

PN 900 076 078 02, any decent hardware store should have those


the dipstick

29.5 cm from end to end

min mark at 2.8 cm from the tip
max at 9.2 cm

[Jack Olsen]

The dash oil level gauge only means anything when the car is stopped, on a level surface, with the engine idling and the engine temp at or near 180 degrees. Under most other conditions, it will flop all over the place.

The dipstick is more reliable, but the car still needs to be idling and warmed up and on a flat surface. You want to fill it to the midway point between the two marks on the dipstick.

[Tyson Schmidt]

The gauge will peg full if the wires are disconnected, so check the connections, including the ground wire at the sender. Any resistance in the circuit will give a false high reading.

[Yellowbird RS]

only trust in the dipstick

[Deschodt]

Jack, that is exactly what I did - this is not my first 911 - but I've never had the gauge peg so high while warmed/idling or while the motor is turning high revs, so it kinda looked high to me... Thanks for the reply though ! BTW just saw black beauty 2 on a pelican ad in Panorama, beautiful ! How does it feel to be famous ? ;-)

Tyson - much appreciated, but like I said in my post I know it is not a short, the gauge does work - it reads low briefly if I get hard on the gas but returns to reading high if it's turning stabilized revs, even high revs. Looks overfilled ! My SC did not act that way, it read low or empty most of the time except idling - trying to figure out if the gauge needs calibrating or if my dipstick is too short, which might explain why the new gage/sender indicate too much oil in the tank.

Svandamme, thank you !!! That was my question and it seems that indeed my dipstick is short by about 5 cm per your measurements !! If that is true that would explain why the oil level reads high even on level ground and fully warmed up - even though the dipstick reads fine! Short stick = more oil !

Does anyone have any idea what model of 911 was the cut off between short/long dipsticks ? I know my 83 SC has a longer one than this car (73.5), which seems incredibly short and might have led me to overfill....

[Tyson Schmidt]

Originally posted by Deschodt

Tyson - much appreciated, but like I said in my post I know it is not a short, the gauge does work - it reads low briefly if I get hard on the gas but returns to reading high if it's turning stabilized revs, even high revs.

Who said anything about a short?

If the connection is poor, the gauge will work like usual, but just read a little high. The sender is a variable resistor. The higher it swings, the higher the resistance. So if the connections are dirty or corroded, or just not making good contact, etc. it will make the gauge read artificially high. It's very common for the ground tab that sits under the lower right sender retaining nut to be loose or making poor contact.

[PorscheGuy79]

tyson knows all

[javadog]

Greg,

The dipstick in 1973 shows to be 911.107.731.01, according to PET. There was a different dipstick used from 74-80 and another one from 81-89. Ironically, I probably have one of each in my warehouse but I can't make it over there this week. For what it's worth, the one used from 81-89 is 295mm long, with the low mark 25mm from the lower end and the high mark 85mm from the lower end. The later ones have the part number stamped on them; take a look at yours and see if you see a part number.

One other thing, if the dipstick proves to be the correct one and the electrical connections are good. You said that you changed the sending unit. Are you sure you installed the correct sender?

JR

[Deschodt]

Tyson - I stand corrected... Thanks for your reply and clarification. You are right, it could be that the resistance is too high. I cleaned the connectors at both ends when I installed a new sender and rewired the gauge, but I cannot vouch for the wire itself...

If that is the case I can live with it but I'd like to know for sure so I guess I'll have to investigate the dipstick length issue ;-)

Javadog - I can't be sure, I ordered a sender from Pelican for my model year and it looked 100% similar (just new). I'll just have to find a kind soul with a 73.5 and ask him to measure his dipstick ;-)

Thanks guys !!!

[Joe Bob]

12 quarts.....ya got a lot of wiggle room.

[RSBob]

Be sure you check that you have solid connections at the sender - Give each wire a good pull at the sender and make sure they are not corroded as mine were.

EVen though the connections were tight, the ground only had about 4 good strands left. I unfortunately didn't catch on until I received a new sender, installed it and then noticed the ground wire twisted a little too easily. Now I have a spare sender - just need another cork gasket.

[Bob Schaefer]

If you're serious about the oil level gauge reading correctly, try this (it worked for me after I installed a new level sender in the tank last fall):

After properly filling the oil tank as shown on the dipstick at temp, disconnect the temp sender wire and use a hand held volt/ohmmeter to measure the resistance across from the sender lead to ground with engine idling on a level surface. Record this resistance for later use.

Remove the level sender assy and place it on a clean surface. Now reconnect the lead wire to the level sender and ground the sender housing to the car. With the ignition on, move the sender until you find the proper position that indicates 'full' on the dash guage, and measure the corresponding resistance across the sender.

Disconnect the sender from the car. With the sender on a clean flat surface that you can mark on, hook the voltmeter to the sender and move the float arm until you see the same reading you got at idle. This shows the proper float position relative to the sender housing when the oil tank is at the full level on the dipstick. Be sure to make a mark on the paper for the float position and for the mounting holes for the unit while the assy was laying flat.

The final step is to carefully bend the sender arm to get the guage "full" resistance with the float in its proper dipstick "full" position as marked on the paper.

This worked for me and took maybe an hour or so. Now the guage reading matches the dipstick.