'67 S Oil Temperature

[Bob Schaefer]

Hello – My car is a stock, thoroughly restored / rebuilt ’67 911S.

After seeing the oil temperature continuing to climb at 230 F @ a steady 60 mph and 70 F ambient, I removed the thermostat and observed it was not opening at all on a hot plate. Now, after thermostat replacement, the oil temperature stabilizes slightly over an indicated 210 F @ a steady 60 mph (level road) with an 80 F ambient. (Interpolating between the 210 and 240 gauge graduations, it looks like maybe 215 F.)

From what I remember seeing on this board, “slightly over 210 F” is still slightly high for this car. I do find comfort that driving my car now will probably not risk engine wear / damage due to high temps, but I’d like to be confident the oil / cooling system is functioning correctly for my car. The old thermostat appeared to be original (or at least not new) and so does the case mounted oil temperature sender. I’ve no idea about the condition / calibration of the oil temp gauge.

Questions:
1. Am I correct that 210 F is a little higher than normal for this car? Should I investigate further, or just leave well enough alone?

2. If I do decide to dig into this, I’d like some confirmation that the indicated temp is true before pursuing other things (oil cooler plugging, etc). I’m considering removing the temp sender and dipping it in boiling water while connected to the gauge to check the indicated gauge reading @ 212 F.

3. Can anyone tell me what the electrical characteristics of the oil temp sender are? Is the output electrical resistance vs temp? If so, anyone have an idea of the desired electrical resistance at 210 F?

Thanks,
Bob S.

[Bob Schaefer]

'Guess I've answered my own question.

Putting the sender in boiling water revealed a gauge reading of about 225 F. Therefore when the guage was indicating about 215 F during operation, that true temp was less.....probably around 200 F. I notice that the ceramic insulator on the sender around the electrical tab has a crack.

I'll replace the sender, and should be fine.

Thanks.
Bob

[Rick Cabell]

Bob,
Am I on the hot seat for not putting new sending units in??
I usually use those $100 laser hand help units, (that shoot the little red dot) to check actual temp. I have tested those little units, and they are pretty dam accurate. I guess a new sender is in order.

[roblav]

I just ran into a similar issue yesterday, with both my oil temperature and oil pressure sending units. I had swapped out engines, putting the 2.2S engine in the '66 car (green gauges), and after starting it up, the oil temperature gauge now read very high and the oil pressure gauge very low (both not good). So then I swapped out sending units and all is OK. Perhaps the '70 vs the '66 gauges have different resistance.

[schmidt]

Sending units always have calibration numbers on them, this number should be the same as the HIGHEST reading number on your gauge.

[hdavis]

Jeff, could you please elaborate. You mean you can calibrate the sending units instead of replacing them?

[72targa]

Hello – My car is a stock, thoroughly restored / rebuilt ’67 911S.

Would love to see pictures...

[Bob Schaefer]

The more I investigate this, the more confused I get:

Here’s what I know:

1. After replacing the non-functional thermostat, my car doesn't seem to be overheating. The best I can tell is that the oil temp is about 195 – 200 F at a steady 60 mph with 80 F ambient.

2. Under this condition, with the ‘old’ sender, the gauge indicates slightly over 210 F, maybe around 215 F.

3. With the sender immersed in boiling water on the stove, the gauge indicated a hair under 225 F.

4. After installing the replacement sender from Porsche, the gauge indicates about !?! 260 F !?! under the 60 mph / 80 F ambient condition described above.

5. I put both senders into water and measured the electrical resistance of each as a function of temperature from 75 F up to boiling. There was very little difference……within 0.5 % over the range of 75F to 212 F! (Resistance measurements were taken every 10 deg F.)

6. Here’s what is stamped into the hex flats of the senders:

“New”-----------“Old”
200 C-----------200 C Max
12-24 v---------24 v Max
VDO-----------BeruIreland
----------------08241 31020
7.67------------1.00
901.741.632 00---901.741.632 00

7. After reinstalling the “old” sender and seeing the indicated oil temp again at about 215 F, the resistance was measured to be 153 ohms…..about half way between what was measured at 190 and 200 F on the stove.

8. Wayne Dempsey’s 101 Porsche Projects book states that the sender and gauge must be matched (intended to be used together), and that wrong combinations will give erroneous readings.

MY QUESTIONS: I’m relieved to know that my oil temps are ok, and I can probably live with the gauge error I have now, but I’d like to correct it if possible. Can anyone offer any solution for what to do? Is there a different sender or gauge that I should be using? Is there any way the gauge can be recalibrated to properly read temp either with the “old” or “new” sender?

Rick - Now way do I fault you in any way for any of this!!! When I took delivery of the car from you, the gauge was working properly. I don’t think any reasonable person would expect that each and every component would have been replaced during restoration…..even ones that were working properly.

Here are a few pics of Rick’s handiwork for those who are new to this board or don’t recall the car from a couple of years ago. I'll let them speak for the quality of Rick's work.

Best Regards,
Bob

[Justin]

Earlier in the year I also had problems with oil temps. My engine, although rebuilt 12 years ago, had sat for all this time (never fired with assembly lube) and only had a few hundred miles on it when I started noticing I had an issue with temps. When it was 85f outside I was getting up to 215-218f.

I took the sender out (original from '67) and took my gauge to the VDO servicer/distributer here. They used a new sender and calibrated it to my gauge. I think its more that they tweaked the gauge to work with the new sender. After that it was worked perfectly.

I also did some other things to lower the temps as I think I was actually running a little warm. Its funny, based on comments here, knowledgeable people in Melbourne, Rennlist, etc, people seem very polorized as to whether 2.0 litre engines run hot or cold - people seemed pretty divided on both camps. Some people said they don't get over 180 max, while others regularly saw 220f and didn't think it was a problem. I also had people that used the sighted IR temp sensor and swore that it was accurate, but in my situation I found it was (when shot at where the sender is located) about 10-20f low of the actual. You might get more mileage with one but I wouldn't rely on it after my experience.

Anyway, the engine was running at peak temp around 215f and was highly variable. I could be doing 65mph and temp would be around 190f and then the sun would come out from behind the clouds and with nothing else changed the temp would rise to 215+ (very sensitive).

The two things that were done to lower temps was change the engine shroud to a later T one (for carbs) that had the cooler duct. That change was good for 15-30f drop. I also had the crank pulley changed to a larger model, but had that changed back after I couldn't crack 140f no matter what I did. The other day it was in the mid 70s outside and my engine temp got up to around 170f with spirited driving (with only the shroud change). I am sure when the ambient temps get up to 85+ I will see 180-190f as its only just starting into summer down here.

Good luck! And, BTW, great looking car

[e72phil]

Is everyone here just blaming their gauge only or do some oil coolers need a good clean out as well ?

we just gae my 2.2 T engine a birthday with a really good clean (out of car) and it was surprising to see how much crap was trapped in the oil cooler channels. Mine was the std BEHR unit mounted at the engine.

We ran the car long and hard last weekend in warm spring weather and never saw over 210 C. Maybe its your oil cooler ? When was it last cleaned out ?