Gauge problem...sender-gauge compatibility?

pwd72s · 03-16-2003, 04:54 PM

The problem: When Evern bought his 1971 911E, somebody had previously installed a later model (I think SC) combination temp/pressure gauge. This makes for a funny looking dash, so we obtained a used gauge from Jim in sacto, parting out a '71T. I sent the gauge to N. Hollywood speedo, where it was refurbished and checked for function. I ordered new sending units for a 1971 from Pelican...for the temp & pressure gauges, also for the pressure warning light. Now the question...should Evren replace all the sending units before plugging in his refurbished gauge? I mean, let's say the sending units were to match the later gauge, could using them on the earlier gauge hurt the gauge? Or, would it be okay to experiment, just plug in the gauge, see if it works okay in case the P.O. left the '71 units in without changing them for the later model gauge? Are the sending units "tuned" for the gauge over different model years? If so, is there a multimeter to determine if the sending unit and gauge will match up? If you guys knew what we went through in time & arrangements just to get these pieces to Istanbul, you'd know why we want the job to be well planned out before the switch back to stock is made. Tell ya guys, our hassles here are nothing, compared to Evren's, when it comes to parts...we're mightly lucky here is the USA...
Warren? John? Jim? Ron? Anybody?

pjv911 · pjv911's Garage

I had to change the temp and pressure senders when i put a 2.7 in my 69`. I did hook it up and it was not right. I forgot what it did wrong but there was no damage to my gauge. Im sure someone will offer some better info but i figured I would add my 2 cents anyway

Kurt Williams

tryan · 05:11 PM

from a persons earlier post, the sending units for the oil pressure gauge changed in 68 ish. another person had a temp gage that got colder as the car warmed up. so , no. i would not hook up the gage until i was sure.

i would have evern check the part #'s on what is installed and compare that to the proper year / gauge sending units. you might not have to buy any senders.

edit . look at the date stamp on the gage to be installed and check that years senders number in pelicans catalog to what evern has installed. i think the proir posts where for the green faced units.......................... how's you period button?

pwd72s · 03-16-2003, 05:33 PM

........period button still stuck! Sorry, but it's a habit that will remain with me for the rest of my years. Good idea on the date stamp thing. My car's temp sender still has a date stamp of 4/72. It left the assembly line on 7/72, so this makes sense? So...(there I go again! do it while I'm thinking of what to type.) if Evren's later than '71 gauge works, we should assume it has the later senders that may not work with his gauge? All the new senders already purchased and are now, with some effort, in his hands. The question is whether he should use them, or keep them as spares?

tryan · 03-16-2003, 05:48 PM

i would check the #'s on the existing sender against the new matching ones. somebody said that theirs lasted 30 years....

i would install the new ones and pack rat the old ones as spares. unless they are taxed as personal property in istanbul.

yes, we piss and whine, but we are very lucky.

studeb · 03-16-2003, 07:55 PM

i think that he can plug the gauges in and try without changing the senders. i think that the only changes to the gauge after '69 (until the 90's) are the markings on the gauge. Some have numbers some don't. Electrically they are the same. I doubt that the PO would have changed the senders.
If it was my car, i would plug them in and fire it up. If the needle pegs to top when you turn the key, you need to change senders. That is what i have seen for incompatability problems with temperature guage. Just mark the wires when you remove them from the existing gauges. There will be three terminals per guage: "+" "G" and ground.
You can't really go wrong.

evren · 03-17-2003, 12:23 AM

Thanks for all the input, guys!.. With Paul and the Pelican board on my side these are fun problems to have.

So, where does the sender for the low oil pressure warning light go? I've located the larger cylindrical oil pressure sender (behind the air cleaner housing) and the oil temp. sender (to the lower right of the fan, p.211, 101 projects...), but I can't find the last one. If I can't find it I suppose I can try it with the old sender in place, though i'm not sure if there is a way to test it to see if it worked or not....

pwd72s · 03-17-2003, 07:49 AM

warren? john?

Superman · 03-17-2003, 08:09 AM

The switch for the oil pressure dummy light is at the rear of the engine, mounted to the breather plate in the center of the engine.

studeb · 03-17-2003, 08:43 AM

I thought the oil pressure can came in two versions. One for pressure only with one tab, and one for switch and pressure, with two tabs.
I think the breather plate switch is for a thermotime coupler, there isn't any oil in there, just vapor.

Superman · 03-17-2003, 08:54 AM

I could be wrong, but I do believe that the oil pressure switch is back there. I have two temp sensors, but they are both in the chain housing covers.

tryan · 03-17-2003, 12:44 PM

my 72t with s gauges. the big can above the flywheel at the case halves split/ breather is the mechanical oil pressure gauge/gage sending unit. the oil temperature thermo sensor is on the block at the right side cam/tensioner oil line. my it's to late you blew the motor light does not function and i have not a clue to the senders location. green wire w/red stripe.

pwd72s · 03-17-2003, 01:05 PM

Thanks Tryan...same thoughts here...except another thought hit me with a D-OH!, about the same time the morning coffee kicked in. A light bulb is a light bulb. As long as Evren's present warning lights function, there is no gauge incompatibility to worry about, right? If the sender works, which model it was made for shouldn't matter. Oil pressure is oil pressure, volts are volts, and a light bulb doesn't care...

tryan · 03-17-2003, 01:43 PM

.....my handed down from generation to generation vega would flash the oil pressure light on every corner even at the full mark. i never used fresh oil, just the old stuff out of moms buick.

i drove the honda so long with the low fuel light on, it eventualy burned out.

i did not even think i had an oil pressure light until you made me look. i still develop 60 psi at 3k with the oil hot ,but the pressure gage is quite scary at idle. gauges are the most accurate in the mid range so i ignore it.

if my idiot light did work, i would probably develop a sever case of depression. i am waiting to see what develops with the cam tower oil restriction mod.

the color code shows a green wire with a red stripe for the idiot light. i would assume it would be near the mechanical pressure sensor, but supers post make me think it is hiding behind the dizzy. as paul said, if it worked on the old dash instrument, it will work on the new one. most vw idiots lights are 4-6 psi.

pwd72s · 03-17-2003, 01:46 PM

Super's car is an SC, I believe they may have a different pressure sensor mount, closer to the fan...hidden behing the (ugh!) air conditioning compressor....is this right, Super?