Temp Gauge on a ’69 911T

I have a ’69 911 which I have now owned for 6 months (first Porsche). Recently I had the temperature sending unit replaced, to remedy an inactive gauge. The gauge now appears to work, moving off the initial white band after approx. 10 minutes of easy driving.

My question is that despite the weather and driving, the gauge doesn’t seem to move beyond the quarter to half mark, is this reflective of the normal cooling performance of these vehicles? Do I need to have the gauge looked at? Is there a simple way to test the gauge’s correct operation? The car does not have an oil pressure gauge so I cannot detect excess engine heat through a drop in oil pressure due to thinning.

The last time I tested this involved sitting in a traffic jam for approx. 20 mins on a hot day (32C((89F)), during a lengthy trip, which later involved some fairly hard driving. At no stage did the gauge read over the half way mark. I should also add that there were no noticeable changes to engine performance or idling at this time.

The subject vehicle is a 911 T, 2.0 litre rebuilt 30k miles ago. Pressure fed tensioners, electronic ignition, plus the other usual early engine upgrades. The car runs like an absolute dream, is maintained by one of our local P. guru’s who specialises in early P.cars. The vehicle is not a daily driver.

I don’t know whether this is normal behaviour and given we are in the middle of an Australian summer (37C ((99F) today) I am conscience of cooling performance. The only respite we get from the heat this time of year is hearing how you guys freeze on the other side of the planet!

Kind thanks in advance for replies and advice.

Paul, It isn't freezing in West Texas, it was 85 F last Thursday, and 78 F here today! I think you could test the sender/gauge combination in the car, but off the engine by removing the sensor from the engine block, and rig up a test lead extension for the sender lead to sensor, and a temporary ground strap to the body of the sensor, then take a small pan of water and immerse the sensor in the water, testing at a minimum, at around 160-180 F, and 200-210 F (boiling water) ... you could use motor oil, or vegetable oil in the pan if you didn't mind the mess, but I think you should at least check your comparison dial thermometer from the kitchen in boiling water for accuracy, first.

It does sound to me like your gauge-indicated temps are low for summer driving!

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Warren Hall
1973 911S Targa

Warren,
Thanks for the advice and the quick reply; I will test the gauge as per your advice this evening. The gauge in my car does not have labelled graduations so where would you expect the needle of the gauge to appear at either end of the spectrum you mentioned?

Warren,
Thanks for the advice and the quick reply; I will test the gauge as per your advice this evening. The gauge in my car does not have labelled graduations so where would you expect the needle of the gauge to appear at either end of the spectrum you mentioned?

Paul, The graduated marks are non-linear, starting at the bottom, 120, 180, 210, 250, and 300 F. The 210 F mark is about two or three 'needle widths' below the 9 o'clock level, and the 180 F mark is only up about 25% of the sweep range up from the bottom. For all practical purposes, you NEVER want to see that needle above the 9 o'clock position, which is what I judge to be an 'imaginary' 230 F mark!

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Warren Hall
1973 911S Targa

Thanks Warren, I'll let you know how it works out.