gas gage - sending unit confusion

[Mike Webster]

Pagoda Scholars,

I have a 230sl (built in December'65) which was restored about 5 years ago. My problem is my fuel gage is reading empty when the tank is more than half full. Thinking I may have a crud problem, I removed and cleaned the unit (it's the cylindrical style). Every thing seemed to be in order so I reconnected the unit and found the same result. After researching this site I thought I had had a sending unit for a 280 so I purchased a new 230 VDO unit for $150.00 made for chassis numbers #008954 and newer (mine is 014654). It appeared identical to my old unit, but what the heck, I bought it so I put it in. Same result except I'm now $150.00 poorer. Now, I think I have may a 280 fuel gage with a 230 sending unit. Before I go off and spend another $150.00 for a new 280 sending unit, does anyone have any ideas?

Mike from Detroit
230sl DB180 silver/red

[jeffc280sl]

Hi Mike,

Does you fuel gauge read full when the tank is full?  I'll assume yes.  The problem may be a matter of electric resistance.  As you know the cylindrical sender has a float.  This float is supposed to move up and down with the fuel level in the tank.  As the fuel level drops the sliding contact on the side of the float ioncreases resistance.  As this happens voltage drops to the gas gauge and the needle falls.  Let's assume for the moment that the problem is not with the sending unit.  I would check the wiring from the sending unit to the gauge with an ohm meter. There are 3 wires on the sending unit.  One goes to ground, another to the low fuel light and the third to the fuel gauge.  Fuse 5 feeds the other side of the low fuel light and gauge.  There is a large connector under the driver dash that feeds the instrument cluster.  Sorry I don't know the wire color or number of the gas gauge stuff.  I would check all of the wires and measure the resistance between the connector for fuse 5 and the gas gauge.  As the you move the float up and down the meter should change.  Does this happen?  What are the readings when the gauge is up (full), 3/4, 1/2, 1/4 and all the way down (empty)?  If the readings are good I would say the gauge is inaccurate.  Maybe dirty?  Clean the pins and connector well.



Jeff C.
1970 280SL 4-speed

[JimVillers]

I also just bought a sending unit for my "1967" 230SL (built in 1966).  The part number I received is 110 542 12 04 64.  The "empty" resistance between pin "G" and the brass pin is 65.5 ohms.  The "full" resistance is 4.6 ohms.  

I have not installed it yet so I don't know if it will work correctly or not.  If yours is the same, I'll just plug it into the connector to check the gauge compatibility.


Jim Villers
190SL, 230SL 5-Speed, 190E 2.3-16 Kompressor

[jeffc280sl]

Thanks Jim,

That's great information to know.  Do the readings track nicely between full and empty?  Assuming yours is good, at half full Mike's could be reading 65 ohms which would indicate empty on the dash gauge.  If so, its the sending unit.  I suspect Mike's sending unit should read something like 35 ohms at half full.  If so, I'd check grounds, connectors, wiring and lastly the gauge.  You know how hard it is to pull the center cluster and what other jobs it leads to while out.

Jeff C.
1970 280SL 4-speed

[JimVillers]

Jeff ... It is hard to tell the readings at "half" with the unit not installed in the tank.  I can measure the resistance as the float moves from one end of the cylinder to the other but I can't see the float to estimate where it is.  My assumption is that the resistance change is linear from empty to full.

Jim Villers
190SL, 230SL 5-Speed, 190E 2.3-16 Kompressor

[hauser]

I'm not sure if this helps but when my gauge went bad I was getting a reading of 3/4 when it was just about empty.  The times that I would fill up it would still read 3/4.  Once the new gauge was installed the problem was cured.

1969 280sl 5 spd
Gainesville, Fl.

[ja17]

Hello Mike,
I think some of the early cars had the lever type sender. These do not interchange. I am not sure whene the break point was. Of coarse as hauser states, it may be the guage in your case also.

Joe Alexander
Blacklick, Ohio

[German Dude]

Mike,
I have a 64 Pagoda. I did have the cylindrical shaped sender in it too. It showed empty when the tank was full, and slowly crept up when driving. An empty tank would produce a half full showing.

I am sure the cylindrical style sender is the problem. You need to put in the old-style sender which has an external float. I put one in and it worked like a charme. Installing is the easiest job you can think of - just make sure the tank is almost empty. Well, you have done it before so no need to tell you how.

I have now a working gauge which bounces happily at turns - just the way it is supposed to be.

You should be able to sell off both cylindrical senders and get a float sender without having to shell out too much money on top. SLS will sell it to you.

Juergen
64 230SL #2933, 4sp, signal red, white hard top
93 Citroen XM station wagon

[A Dalton]

>> Mike,
I have a 64 Pagoda. I did have the cylindrical shaped sender in it too. It showed empty when the tank was full, and slowly crept up when driving. An empty tank would produce a half full showing.
>>

 Correct. The early .042 used the external float/arm and these had a circuit that used higher resistance at full/lower at reserve.
 Resistance specs. for early units are:
 Full-180 ohm, +12/-2
 1/2-100 ohm, +/- 5
 Reserve-10 ohm, +/- 4

[Mike Webster]

Pagoda Scholars,

Thanks so much for you're input. Some of my findings:
1) I really beleive I don't have a wiring problem because all the wires appear to be new, everything else works fine and the readings are consistent.
2) I thought I had a cylindrical style sending unit because thats what it shows in my 230 BBB parts book. Upon looking further investigation, I found that my book is a Janurary 1967 edition, which superceeds the December 1964 edition (rookie mistake). Since mine is a '66, I beleive Juergen and Joe are on to something, mine should be a float style sending unit. Oh, those dreaded engineering changes!!

Since my car is restored, I don't know if it has the origional tank. Before I go SLS and purchase a float sending unit, would it be possible someone could provide these answers:
1)Is there a difference between earlier and later tanks?
2)Is the mounting flange and the connections the same for a float style vs. a cylindrical style?

Mike (still confused in Detroit)
1966 230SL DB180 silver/red
2005 Chevy Impala (great car, no kidding!!)

[A Dalton]

The sender unit change on .042 was at chassis 008954 and on.
 Up to then should have the exterior float system.

 These early units can be diagnosed by simply unplugging the sensor and substitute a 100 ohm resistor [ Radio Shack] from the gauge feed wire to ground . The gauge should then read 1/2 full.........
 That should be terminal G at sensor

[A Dalton]

Later unit , if anyone is looking..

 http://cgi.ebay.com/ebaymotors/MERCEDES-108-109-111-113-FUEL-LEVEL-SENDING-UNIT_W0QQcmdZViewItemQQcategoryZ34198QQitemZ4577742595QQrdZ1

[hands_aus]

Arthur

Did the 'early' 250SL have the external float sender or the cylindrical sender?

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[A Dalton]

quote:Originally posted by hands_aus

Arthur

Did the 'early' 250SL have the external float sender or the cylindrical sender?

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

 cylinder style... [only early 230 used ext. float.]

[German Dude]

Mike,
the connections are the same.
You have 5 or 6 small bolts there. Fits like a glove.

I am positive all you need is an external float sender.

Best,

Juergen
64 230SL #2933, 4sp, signal red, white hard top
93 Citroen XM station wagon

[Mike Webster]

Jurgen,

 
Another rookie question, who is SLS? I tried Google, and I get no hits.  

Mike

[A Dalton]

http://www.sls-hh-catalogue.de/bin/dbframes.phtml?mid=IN02

 Item #3 ..part 247016

 The gasket is the same for either unit.  The float goes to the right of the tank. The bolt pattern is off-set for this orientation.

[Mike Webster]

Thanks for the info, I ordered the part from SLS. Will keep everyone advised.

Mike (a little less confused in Detroit)

[rwmastel]

quote:Originally posted by German Dude

I am positive all you need is an external float sender.

But Mike's VIN ends in 014654, so according to info in this thread, his car would use the cylinder style not the external float style.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[hands_aus]

Arthur,
Thanks for the info.

Just checked/cleaned mine because the gauge shows almost empty when half full.

This is a 108 replacement sender because the sender that was in my car was way too short.
This unit is about 40mm longer and I still have the problem.

Still not accurate but I have been living with it for 2 years now and know how it works.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[A Dalton]

BS
 Is there a part# on the sender.

 All the 108 senders I see are the same # as 113 cyl type.
Even the 4.5

[hands_aus]

quote:Originally posted by A Dalton

BS
 Is there a part# on the sender.

 All the 108 senders I see are the same # as 113 cyl type.
Even the 4.5

Arthur,
I had another look, there were no MB numbers but this is what I found.

OLD cylindrical SENDER that was originally in CAR

TOP MARKINGS

VDO      nur f Benzin

11  66   <<is this the make date?    
21/169  
LENGTH   150mm

RESISTANCE  WITH FULL TANK   59.4 Ohms
RESISTANCE  WITH EMPTY TANK   118.4 Ohms


NEW cylindrical SENDER FROM 108

TOP MARKINGS
VDO   
xxx  73   
21/293
673

LENGTH   190mm  approximately

RESISTANCE  WITH FULL TANK   4.5 Ohms
RESISTANCE  WITH EMPTY TANK   65.5 Ohms

Neither of these senders give me a correct reading that is why I asked about the 'EARLY' 250sl and the float type sender.

There was a discussion about this some time ago and it came out that the gauges were different for the different types of sender.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[German Dude]

Rodd,

I know that with respect to the VIN, it should be a cylindrical sender. But the symptoms are identical to what I experienced, hence my confidence. I even get the red low fuel warning light - which kind of made me happy.

Juergen
64 230SL #2933, 4sp, signal red, white hard top
93 Citroen XM station wagon

[Mike Webster]

Pagoda Scholars,

I beleive Jurgen's suggestion will work.  After I install the float unit, and if it works, I'll offer my slightly used cylindrical unit free as a token of my thanks to anyone who needs it.

I'll keep you posted.

Mike in Detroit

[n/a]

I'm quite certain the float sender will solve your problem.  I had this exact problem with an early 1964 230sl we had.  When I installed the float sender, everything was perfect.  It is possible that somewhere along the way someone swapped out your gauge to be the early type.

don't always trust the VIN

-Lewis

'66 230 sl 113042-10-016238
'67 Saab Sonett II #43 of 258
'69 Porsche 911S
'00 Saab 9-3 viggen conv
'02 Saab 9-5 aero