Recalibrating Oil Temperature Gauge 1966 911

[304065]

My oil temperature gauge in the 1966 911 isn't working. Engine type 901/05. If you ground the sender wire to the block the gauge goes to full hot, so it's not the wire or the gauge, it's the sender. Either the sender is kaput, or someone has installed one from a later car with a different resistance value, causing the needle to stay around 140 regardless of operating temps.

Now, I could replace the sender with the appropriate one for an early car. The correct one for a 1965-1968 911 is 901.741.632.00. Ol' Wayne gets about $300 for this baby, other sources have it for as low as $110 (hey, great!).

Has anyone gone the other route, e.g., had their 1965-1967 gauge recalibrated to work with the later oil temperature sender? The modern sender is a whopping $25, and it seems like IT is more likely to require replacement in the future.

I will be calling NH Speedo and Palo Alto speedo with this question but was curious as to whether any of you had faced this issue before. I'm pretty confident that I could get a modern gauge refaced and re-needled for less than the cost of the NOS original part.

[Grady Clay]

John,

The HUGE difference between the early gauge-sending unit is its sensitivity. I have put many early combinations in later cars using the ’68 parts. Very desirable in an SC because of the calibrations and sensitivity.

I would spend some time and find a good used one with the correct date stamp and patina. I’ll bet you can find one in a shop somewhere. What is the date on your failed sending unit?

I judged these cars at the Parade for many years. If I found a nice ’66 converted to later, it would loose points. If I found one with the wrong date on the sender it would be about neutral. One with the correct date and patina would earn a few points.

I know your project is going to be done correctly, within reason. This is one of those reasonable efforts.

Best,
Grady

[Early_S_Man]

John & Grady,

That is the 280° F gauge, right?

From a few pics I have seen posted of the early 'green' scale, and white scale '68 gauge [also 280°F] ... it looks to me that the '69 - '74 gauge with top mark of 300°F is just different scale makings on essentially the same range, that is, the 300°F mark is just a higher mark on the same range dial ...

I have a spare sender [same as below] that I tested [using a Fluke 52 Thermometer and 8800A DMM] on a hotplate in a pan of old vegetable oil a couple of years ago ... and I posted the results here from 70°F to 300°F along with the resistance values. That data is in a spreadsheet on a different computer ... but I will see if I can find it, and post it later.

Temperature Sending Unit, for numbered gauge (requires 1 J-123-007-30 sealing ring), 911 (1969-73)
A-641-632-00 $26.90

A potentiometer or resistance decade box could be substituted for the sender to detrermine the required value at say 140°F, 210°F, and 280°F ... if the values are close [within 2 - 3 %] to my test results, then the $26 solution is at hand!

There has been a bit of discussion in the past over long and short nose versions of the sensors, though I don't believe there was ever a definitive answer ... as to whether the '69 -'74 sensor can replace a '65 - '68 sensor in the electrical sense.

I have to wonder if there are generic versions of the early 901.741.632.00 sensor from VDO or other sources that will work???

If the aswer is a positive NO, then it seems like the $97 'update kit' insert gauge could be relabeled in green fairly easy.

[Early_S_Man]

Found the old posting!

I ran a test in the summer of 2002 on a new ['69 - '73] early VDO sender in a pan of cooking oil on a hotplate ... using a thermocouple probe and Fluke 52 thermometer, and measured the resistance at 10°F intervals from 70°F to 300°F.

If you substitute a 1000 Ohm potentiometer for your sensor ... you could test your gauge by sweeping the range, and temporarily disconnecting the pot. to measure the resistance that produces readings at your gauge marked points ... I wouldn't worry too much about the 300°F to 340°F range!

Temp - °F -- Sensor Ohms:
70 1148
75 1000
80 918
90 756
100 607
110 504
120 424
130 357
140 301
150 260
160 219
170 189
180 162
190 142
200 122
210 108
220 92.4
230 82.2
240 73.2
250 64.2
260 57.6
270 51.2
280 43.8
290 39.6
300 35.4

[304065]

Thanks gentlemen. Grady, I hear your point about originality- perhaps an old sender can be found, and I would only have to swap from the orange to brown distributor caps before judging starts! Next time I'm with the car I'll take some pictures of what's installed, and go through the spares box to see if anything's there.

Warren, thanks for the research results. I'll dig up a 1K pot and run some tests on the old gauge and report back here.

[Grady Clay]

John,

So long as the brown cap is electrically functional. Hehehe. I’ll bet some of these serious guys find the original brown and coat the inside with some dielectric insulating material. Probably good for a few hours running.

I should read the current rules. Then, the cars had to start and run. Some got serious penalty from me for fuel leaks. Nothing like burning down a Spyder or 917. There was a contender for the Manhattan that had rust pouring out of the fan pulley after running. The two halves had never been tightened against the intermediate shims (probably not enough shims) and had had been working against each other for some time. It was a 906 and it wouldn’t have made more than a lap or so on the track. Functionality is primary.

I had a friend with a restored P-38. A couple of days before he was going to take me up again, he lost an engine on takeoff at SLC, killed him and destroyed the aircraft. Functionality is primary.

Warren, I’ll look through the parts manuals to see where the change was. It is easy to tell looking at an engine. The early version has a push-on spade from the rear of the 911. The next later versions had a slide on the side connection. I don’t remember the exact year of transition – I used to know.

Best,
Grady

[304065]

Update:

The sender that's in there is original to the car, evidenced by the 2.66 build date. It's also DOA, showing zero ohms.

I stand corrected: when the sensor wire is removed the gauge goes full-hot, when it's grounded, it goes to 140F.

[304065]

Replaced the sender, engine reads 210F.

Replacement sender was made in Ireland by Beru, said "200C Max" and "-24V", and no date code, otherwise indistinguishable from the original with straight tab and long temp probe.