Temperature issue driving me crazy!! Could my gauge be wrong??

[Dana_Drury]

Hi guys,

Some of you might recall I had some questions regarding my 3.0l Carrera getting hot. I have done the following things:

* Replaced external thermostat
* Replaced internal thermostat
* replaced external oil return lines (both uptake and return)

And my temperature gauge is still rising to and staying at 110C in 18C ambient temperatures (and often rising to closer to 120C after 30 minutes of driving). I feel like I am chasing my tail now.

Could my numbered 'C' gauge be out of calibration or the sensor faulty? If so how do I test it?

I have replaced all the major components, the car is not running lean and there were no obstructions in anything. The internal oil cooler is in excellent condition, it has a new internal and external thermostat, and new oil lines to the front cooler)

At the indicated 110C the internal oil cooler is very hot to the touch, as are the oil lines to the thermostat, and the uptake line to the front cooler is hot for about a metre after the thermostat (is that radiated heat as the return lines aren't as hot). The front trombone cooler isn't getting hot after 20 minutes of driving though.

I know the external thermostat is working fine because my original external lines were somewhat crushed, so we took them off, flushed them clean and decided that they might be okay, put them back on the car, drove it, found the same 110C+ indicated and then I decided to replace them. When pulling the old ones off, I found they had oil in them, now there are brand new lines on them.

I am guessing that maybe my gauge is faulty (or the sensor). After speaking to a german Porsche mechanic, he said that in germany, they often had cars that after storage in winter, would display inaccurate readings when brought out and driven in the summer. When I said that it was sitting at 110C he laughed and said that number was often thrown around and he suspected my gauge was out of calibration.

I sincerly hope this is the case, but I want to test it to put my mind at ease. I am happy to get the gauge calibrated, as long as I am satisfied that something else is playing up and my actual cooling system is working okay.

My understanding of the gauge is that the temperature sensor (I believe its located on the right hand side, at the front (facing the engine) of the engine, on the chain tensioner cover?), sends out a certain voltage based on the temperature, so there are two possible issues. The gauge is reading the voltage wrong (or incorrectly), or the temperature sensor is not working properly.

I don't know how to test the gauge, I assume you supply a voltage to it, but I don't know what it should be getting (say .025v = 30C, .05v = 90C) so forth. And also how does one test the actual temperature sensor (and which one is it exactly???)

I am happy to haul it off to the p-mechanic, but if I can narrow it down and say "I've tested the gauge, its 20C out of whack etc". That also puts my mind at ease.

Thanks for answer my questions...

[Wayne 962]

Yikes, the sensor would have been the first thing that I had replaced. A good thermal temp sensor like ones on this page are a great investment:

http://www.pelicanparts.com/catalog/shopcart/DWKS/POR_DWKS_toolsC_main.htm

That will tell you right off the bat if your gauge is off...

-Wayne

[Dana_Drury]

AAAAAAAAARRRRRRRRRGGGGGGGGGHHHHHHHHHHH!

(Falls in a heap). Thanks Wayne.

I am in Australia, I have bought stuff from you guys before but can't wait the time for temperature/thermometer tool to get shipped out to me. How do they work, where would I test the temperature... and what kind of tool should I be getting (looking at the page there are few non contact ones etc?? ).... I will try and get one now.

Thanks again.

[beepbeep]

Dana_Drury:

Temperature sensor is basically a NTC-resistor. It costs 10$ and is pretty much interchangable with other car types.

Change it first and check out the temps, if you still get high oil-temps, measure it's resistance with ohm-meter and check out the chart to see if your gauge is out-of-whack.

Also, temperature-sensor being pretty standard item, you could probably buy add-on 52mm oil-temp meter and plug it in instead of original one just to check.

[Dana_Drury]

Thanks for the suggestions. I don't have a temperature/ohm chart which is something I am trying to track down. The Haynes manual has no information. Does anyone have one they can send me?

[Early_S_Man]

Dana,

Here is the data from a new '73 sensor tested in oil with a Type K thermocuple probe and Fluke Model 52 Thermomete, and Fluke 8800A DMM:

100°F -- 607 Ohms -- 38°C
110°F -- 504 Ohms -- 43°C
120°F -- 424 Ohms -- 49°C
130°F -- 357 Ohms -- 54°C
140°F -- 301 Ohms -- 60°C
150°F -- 260 Ohms -- 66°C
160°F -- 219 Ohms -- 71°C
170°F -- 189 Ohms -- 77°C
180°F -- 152 Ohms -- 82°C
190°F -- 142 Ohms -- 88°C
200°F -- 122 Ohms -- 93°C
210°F -- 108 Ohms -- 99°C
220°F -- 92 Ohms -- 104°C
230°F -- 82 Ohms -- 110°C
240°F -- 73 Ohms -- 116°C
250°F -- 64 Ohms -- 121°C
260°F -- 58 Ohms -- 127°C
270°F -- 51 Ohms -- 132°C
280°F -- 44 Ohms -- 138°C
290°F -- 38 Ohms -- 143°C
300°F -- 35 Ohms -- 149°C

[Dana_Drury]

Thanks Warren, I appreciate it.