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Porsche Crest Center Console Temp Gauge

I previously had an oil temp/fuel combo gauge mounted in the dash. When the car was warm, the needle would sit about half way between the little white hash and the red mark consistently on the combo gauge.

I have now added a center console temp gauge and removed the in dash temp gauge. I am using the same sender with a brand new NOS temp gauge, but the needle camps out maybe 1/8" away from the little white hash, much further from the redline than it did on the combo gauge.

I have only changed minimal things on the motor, by adding SS heat exchangers and a K&N air filter which were done at the same time. I am using the same sender in the taco plate as before. Is the readout on the gauges usually this different?

The only other variable is the ambient temperature, as I am driving the car in 20 degrees or so cooler weather than I have ever driven it before (now that I have working heat). Does this really have that dramatic of an effect? Please help. Steve
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Old 02-12-2005, 06:01 PM
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both gauges use the same sender.....
i too worry that my indash 914/6 style gauge is reading low...
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Old 02-12-2005, 07:49 PM
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Anybody else have any ideas? Steve
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Old 02-14-2005, 06:05 PM
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What can affect the gauge reading and calibration is the voltage on the gauge - assuming the gauges have identical characteristics. I suspect that your 12V is running a little higher in the console than in the dash, due to the nature of the wiring harness (number of loads on your circuit, wire length, etc.). A slightly higher voltage on the gauge will cause the temp reading to be lower.
If you're using the red/wht wire for 12V in the console, one thing you can try is to watch the gauge when you apply the brakes. The console picks 12V off the brake light switch. With the brake light on the voltage drops a little and the temp should slightly increase! If that's the case you can run a wire off your original 12V in the dash to power your gauge, to get the same reading.
Old 02-14-2005, 06:30 PM
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If you want to know your oil temperature, then use a long candy thermometer down the dipstick hole--or a thermocouple with long leads--or dunk the sender in boiling water while still hooked up to the car's electrical system. (Run a ground wire to the threads of the sender in that latter case.) Those will give you references where the needle points for some specific temperature.

Otherwise, you're just guessing "warmer" or "cooler".... Than what??

--DD
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Old 02-15-2005, 01:09 PM
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Steve,
Don't worry about it. It's only a relative readinig anyway. If it pegs, your hot, if it doesn't move, something is defective. The stock oil temp.
indicators in the 914 are about as precise as putting your hand on the top of the engine after shutting down, if you can't touch the case, it's been running too hot, if you can keep your hand on the case for 3 or 4 seconds, it' A-OK.

Phil
Old 02-15-2005, 02:02 PM
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Quote:
Originally posted by philinjax
Steve,
Don't worry about it. It's only a relative readinig anyway. If it pegs, your hot, if it doesn't move, something is defective. The stock oil temp.
indicators in the 914 are about as precise as putting your hand on the top of the engine after shutting down, if you can't touch the case, it's been running too hot, if you can keep your hand on the case for 3 or 4 seconds, it' A-OK.

Phil
I agree, it's almost worthless in it's stock form. I calibrated mine and added tick marks with temps marked from 170 - 210 in 10 deg. increments for water temp. I'm too cheap to buy a real one!
Old 02-15-2005, 03:36 PM
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oil temp gages

I posted this elsewhere a long while ago, but here it is again
if you search for the prior posting you will also find pics of the gages & temp ranges for the various senders


914 high oil temperature

Bruce Anderson
National Technical Chairman
Porsche Panorama, 1990

914 high oil temperature: My 1974 91.E seems to be running too hot. Even with outside temperatures in the 80s, the needle on the oil temperature gauge gets up to about 90 percent of the way to the red zone. Does this mean it is too hot? Could I substitute a calibrated 911 gauge for the 914 console gauge to determine what the temperature really is? If the car is running too high an oil temperature, does it mean there is something wrong with the oil cooler or the air cooling flap adjustment? If there isn't, what can be done to reduce the oil temperature?

Alan Caldwell responds:

This question was the most frequent 914/4 inquiry received during the warm weather months. Causes for higher-than-normal oil temperature can include too low an oil level, blockage of the cooling blower intake or internal passages, improper ignition timing, too lean fuel mixture or a spark plug heat range warmer than specified.

The USA 914 factory installed oil temperature gauges never included any numbers on them and the owner's manual advises that the needle will normally vary up and down within the white zone depending upon ambient temperature and engine load, but the owner is not required to take any special action unless the needle goes into the red zone.

Most Porsche owners don't trust gauges without numbers and the 914/4 situation was made worse by the first console oil temperature gauges (914.641.118.20) in the 1973 models showing very little needle movement regardless of conditions. The white zone on these early gauges was about an inch wide and the red zone about three-fourths of an inch. The sender unit with these gauges had a temperature value of 200C (392F) stamped on the headend. the normal operating range of 160 F to 210F occurred over a small portion of the white z6ne (Figure 1)

In 1974, a new gauge (914.641.118.30) was introduced which had a much larger white zone and much greater needle travel than the earlier design. The sender unit that came with the newer gauge remained the same (part no. 039.919.268)

The first step in oil temperature peace-of-mind is to find out just how high your oil temperature really is.
The quickest and least expensive way to find where you are is to determine at least one pertinent calibration point on your existing gauge equivalent to 212F.

The most convenient time to do this is during an oil change when all the oil is out of the engine. This can be done by removing the gauge from the car and also removing the sending unit at the left forward side at the bottom of the crankcase. (Keep track of the way the wires are connected to it).

Connect a positive (+) wire from the battery to the gauge (+) terminal and then run a connecting wire from the gauge to the center electrode on the sender. A ground wire from the sender base to the gauge ground (-) and also to the battery ground completes the circuit. The sender can then be immersed in boiling water and the needle on the gauge should stabilize at the point on the scale equivalent to 212F.

This procedure is only approximate since increases and variations in line voltage with the engine running may cause slightly higher needle positions. However, the results should be close enough to tell you if you have a problem.
Even the single 212F point obtained with boiling water is a significant position to know on your temperature scale, since it is toward the upper end of the normal operation zone of 160F to 220F.
If you want to get really scientific and have an oven or candy thermometer, you may be able to also check a wider range of temperatures up to the red zone by using cooking oil instead of water.
This latter type of calibration was used to arrive at the temperature scales shown in Figure 1. Since we found three different 914/4 sender units stamped with 120C, 150C and 200C, the primary combinations of gauge and sender were also calibrated.

On my 1973 914/2.0, my calibrated gauge has read as high as 200F on a warm day under normal driving conditions and up to 2501F for sustained track driving. When coming off the track, the temperature quickly falls to the 200 F region. If your car has the 2000C sender and the late style gauge, it is possible that your oil temperature at 90 percent of the way to the red is about 250F and is probably too high for continuous running at that point.

Although a calibrated 911 gauge and sender would work in the 914, it would not be particularly convenient in size unless you wish to mount a 911 combination oil temperature and oil pressure instrument in the dash and put a separate fuel gauge in the console.

Alternatives include a 914/6 combination instrument or the similar 914/2.0 combination instrument that included an oil temperature gauge and was used on the two-liter cars that did not have the appearance group and console.

The 914/6 combination instrument (914.641.101.10) is shown in Figure 2. The oil temperature gauge portion of the instrument has five factory calibration marks. The marks are along the upper edge of the interior face and are not very easy to see without looking at a very small angle or removing the temperature gauge portion of the instrument by taking out the four screws in the back. The calibration points include 50 C (1220F), 68 C (154F), 109.5C (229F) when the needle is vertical, 129 C (2641F) at the beginning of the red-shaded zone and 144C (291F) at the beginning of the solid red zone. There is also a red oil temperature warning light at the high end of the scale that was planned for use with the sportomatic cars, but not connected to anything on the manual transmission cars.

The 914/6 oil temperature gauge uses a different sender than the 914/4, part number 901.641.632.00, which is a 150 C unit. A calibration check of this gauge similar to that used for Figure 1 is indicated in Figure 2. The gauge readings were found to be within five to ten degrees of the factory calibration marks from 160F upward.

The four-cylinder, two-liter cars without console used two different combination instruments with oil temperature gauges. The original gauge of this type (914.641.101.30) was used until the end of the 1973 model year and pictures of it show a wide red zone similar to the 1973 console gauge. In 1974 and later cars, an updated gauge, 914.641.101.50, was used with a smaller red zone. I was able to borrow one of the 1974 and later gauges and found, like the 914/6 and 911 gauges, it had factory calibration marks on the edge of the gauge face indicating that the bottom of the white scale was 30C (86F), the beginning of the red zone was 156.7C (314F), and the middle of the red zone was 170C (338F).

Figure 3 shows the 914/2.0 combination instrument and the oil temperature calibration using a 200C sender and the same method as for the console gauges. The results were very close to the factory calibration marks: the calibration thermometer indicated 308 F at the beginning of the red zone instead of 314, which seemed within the accuracy of the method and gave some confidence that the rest of the numbers weren't too far off. The overall calibration of the combination instrument was also reasonably close to that of the console instrument with the smaller red zone. In the gauges checked with the stock 200C sender, the red zone starts at approximately 300F.

A nice advantage of the dash-mounted combination instruments with their removable oil temperature gauges is that small white transfer numerous can easily be added to the face of the gauge so you don't have to remember the calibration. In addition to the Porsche gauges, VDO offers an aftermarket oil temperature gauge with numbers on it (the range is from 120F to 300 F) and the sender specified for it is the 150 C unit. The gauge is somewhat smaller in diameter than the stock console unit (approximately two inches compared to 2 3/8), but an adapter is available which allows it to fit.
We also compared the electrical resistance versus temperature curves of the VDO 150C sender (901.641.632.00) used on the 914/6 with the VDO 150 C sender used on the aftermarket VDO gauge. Below 180 F, the 914/6 sender had substantially greater resistance, so it is probably a good idea to stick with the sender recommended for a given gauge.
Current thinking is that continuous operation of air-cooled engines at oil temperatures over 220-230F is not desirable and will degrade engine longevity. If you find you really are running in the 250F range, you should first check all the contributing factors.
The 914/4 engine oil level needs to be at or slightly over the full mark under warm running conditions. The viscosity range of the oil should be high enough to cover the maximum expected ambient temperatures. Make sure all cooling passages are open and that the intake to the blower is not blocked. Adding the fully-screened engine deck lid that was used on the 914/6 competition cars will also allow more cooling air into the engine compartment.

The thermostatically-controlled cooling air flaps that are designed to assist in initial engine warm-up might be a contributing factor if not properly adjusted or if the thermostat has failed.
Old 02-15-2005, 07:00 PM
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Re: oil temp gages

Quote:
Originally posted by larrym

This procedure is only approximate since increases and variations in line voltage with the engine running may cause slightly higher needle positions.
My experiments with the stock gauge shows it will read a lower temperature as the voltage increases. It's normal for the voltage to run around 13- 13.5V when it's running. If you calibrate at 12V it'll read cooler when installed on the car. To eliminate this variation I wired a 12V regulator onto the back of the gauge. Mine is finally a useful gauge. Even my clock works.
Old 02-15-2005, 07:19 PM
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I hadn't red caldwell's article but I did exactly that test to calibrate my gauge to 212 deg F. a couple weeks ago.

I don't run an alternator so calibrating at 212 deg with 12volt source is perfect.

dr
Old 02-16-2005, 03:56 AM
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Well, the voltage is about the same at both points, and when I relocate the center console gauge to the dash and plug it in, there is no difference in the reading. The needle still hangs out almost right on top of the bottom of the white zone of the gauge.
Does anybody else have the 73' center console gauge 914.641.118.20 installed? If so, where does the needle sit when you are at normal operating temperature? The bottom of the white zone?
I have found out that the combo gauge I had in was the 74' 914.641.101.50 with a much smaller red zone (and different needle travel), so this alone may be the source of my problem. However, it'd be nice to know where the needle usually hangs out with these early console gauges. Steve
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Old 02-18-2005, 07:44 PM
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Steve, do the above test yourself. That will tell you what your temp gauge is reading, rather than someone else's combination of sender and gauge and whatever extra resistance is in the connections on their car and on and on... Far better to actually know, than to say "Well, Bob's car usually runs at the 'E' in 'TEMP', so mine is running cool because it's at the 'T'..."

--DD
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Old 02-22-2005, 10:42 AM
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Run your car HOT. Check various points on the engine, oil filter, etc with a laser thermo and take note.

I couldn't find a spot over 210 degrees with the needle pointed to "P".

KT
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Old 02-24-2005, 06:46 PM
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