Testing oil temperature sender. Help please.

[heimtun]

The oil temp needle does not go out of the little box area on the bottom part of the gauge - E.G. does not go to the "normal" range, the line between the box and the red areas.
I pulled the wire, cleaned the sensor contact and changed the wire connector no joy. I then grounded it and the needle pinned to the top of the gauge - so it would appear that grounds power to the gauge are good as is the gauge.
What resistance readings should I expect from the sender when engine is hot? And/or is there another test I can perform before I replace the sender?
Alternatively, is a reading at the top of the box on the gauge "normal"?
Thanks,
Wayne

[GH85Carrera]

Get a small container that can hold boiling water. Rig up the sender so that the probe part that is normally in the oil stream will touch the boiling hot water. Obviously it should read just under 212 degrees or a nice normal warm side full operating temperature. If not, replace the sender.

[cmonref]

Has this just started after some time of correct operation?

Did you recently change either the gauge or the sender? Mismatches can occur and present the symptoms you describe. When I changed the oil temp gauge in the instrument, I had to change the sender also.

Normal for a 911 would be 180-210, depending on whether the 28-tube cooler or the trombone are installed.

Look at the gauge from the extreme right. Notice a short white mark at midgauge. That is 212*F. There are other marks, above and below that one, but I forget what the temperature indications are for those other marks.

[javadog]

That reading might be normal. You don't specify which gauge or sender you have, or even if your car is a US spec car, or a ROW car, or what sort of oil cooler you have, etc. So, too many variables to give you an answer.

What I have noted is that some cars run that cool. I once had an '80 turbo that never ran very hot. About 180 degrees is all the oil temp I ever saw, and less than that in the winter months. My US spec cars always ran warmer.

You might test the sender and see what temperature you are actually getting when the gauge reads at that value. Or check the oil temp in the tank, when fully warmed up.

For what it's worth, there are several different gauges and they don't all require the same sending unit. Pair the wrong sending unit with a given gauge and you will get inaccurate numbers.

Can't help with specific resistance readings, sorry.

JR

[T77911S]

you dont need to go thru all that trouble.,

just remove the wire from the sender, the needle should go to max, then ground the wire, it should go tto min. if that is good then replace the sender.

you can also check the resistance of the sender cold then warm the engine and check it again. if it does not change it is bad.

[heimtun]

Thanks for your replies. Some answers:

- I've had car for about a year - always showed this reading.
- U.S. spec car with relatively low mileage ~64K - if I believe the odometer.
- Trombone cooler.
- Re T77911S - my gauge acted in the opposite directions, wire off -> needle low, wire grounded -> pin to top - resistance does change as engine gets hot and needle moves.

Gauge style - see photo.



Readings when hot - somewhere above 90C based on gauge - nowhere near center line (100C as described by cmonref) - this would indicate that oil is over 90C (194F) - so I guess I'm within range mentioned by cmonref).

So, maybe all is well :-) ???

[javadog]

The middle of the gauge is much hotter than 100C, so you are probably normal.

JR

[T77911S]

some gagues work different than others in that when grounding the wire the needle goes up or down. all you are looking for is that one way it pegs hi and the other it is low.

look on the left edge of the gauge. notice the "calibration" marks with the temp numbers. that will give you an idea of where "normal" should be.

[heimtun]

Thanks all for your feedback! Based on everything I've read here and elsewhere - it would seem that all is working as it should and that my readings are in the normal range.
More feedback is always welcome if someone sees something I've missed or misinterpreted.
Wayne

[DRACO A5OG]

If it pegged when you pulled off the connector at the sensor means your gauge is working as designed.

Get a cheapo IR temp reader and check the temps at the rear wheel well thermostat.

If at 194F does your oil level rise?

[evan9eleven]

I have the same readings on my 1981 SC.

When I got the car the temp gauge never moved, so I tested the gauge by grounding the wire, it pegged. Ordred the correct sender from our host, and when fully warm the needle now moves but still never gets higher then the top edge of the box. With the car off/cold the needle is as in the picture you posted. Between freezing cold and fully warm the needle maybe moves 3-4mm.

When I get my gauges redone I will get the scale changed and get a new sender. Its hard to see what is going on the way it is now.

On my Dad's '86 the needle goes about 1cm above the box on a warm day, everything functioning fine.

[heimtun]

evan9eleven - Many thanks! It's comforting to hear another similar car reacts the same as mine. Have a great weekend.

[cmonref]

The middle of the gauge is much hotter than 100C

Javadog: that unlabeled white mark at gauge center is 100C/212F per design. The other marks, all labeled, show that the gauge is not linear.