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Factory Temp Gauge Inaccurate


B0oStEr
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Since I've owned my r32 the temp has always read about 3/4 on the gauge where most say theirs runs about 1/2.

It's not actually running hot and once the gauge rises to 3/4 in about 2 minutes from a cold start it stays there.

It doesn't read any higher when driving it hard even on hot days.

Once the motor is warm if I park the car for a 1/2 hour when I restart it the gauge goes to 3/4 in a couple of seconds.

I know the factory temp gauge has a bad reputation but is the problem in the gauge or the sender.

I tested the ohms between my sender and earth with a multimeter.

I don't have a thermometer so I timed the readings during cool down.

At normal operating temperature it read 56ohms.

15 minutes after I switched the car off it read 60 ohms.

After half an hour it was 120ohms.

Dead cold it was 651ohms.

Does that seem about right or should I get a new sensor?

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I'm sure it's been covered before - try a search.

2.5k comes to mind for the sensor resistance when cold.

EDIT: No that's the ECU temp sensor. Don't think it's covered in my workshop manual.

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They are notoriously unreliable in R32's from what I hear and experienced. Mine was probably overheating for a long time before my top tank on the radiator let go of what coolant was left (the temp gauge read pretty normal 1/2 way, and never changed much) and overheated. My water pump had died, and was draining out what I was putting into it.

Re. Your problems, if you car is reaching 3/4 in 2mins, thats pretty quick. Mine takes at least 5mins idle to go up much at all, and has been taking around 8-10mins of driving to get up to 1/2 temp.

Check your water pump is not on its way out, and check coolant levels.

Do yourself a favour, buy a water temp gauge.

Fixxxer

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I have done a number of RB25DET conversions in R32's and I have to use the original RB20 sender to get a correct reading as the resistance profile of the RB25 unit is different. I would suggest replacing the the RB20 item with the original CA or SR item as this obviously has the correct resistance characteristics for the factory gauge.

Cheers

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I'm sure it's been covered before - try a search.

2.5k comes to mind for the sensor resistance when cold.

EDIT: No that's the ECU temp sensor. Don't think it's covered in my workshop manual.

I tried searching but could only find posts on how the factory gauges are crap and nothing about why they are crap.

Re. Your problems, if you car is reaching 3/4 in 2mins, thats pretty quick. Mine takes at least 5mins idle to go up much at all, and has been taking around 8-10mins of driving to get up to 1/2 temp.

Check your water pump is not on its way out, and check coolant levels.

I guess it might take a bit longer than 2 minutes at idle but within a couple of ks it's up there at 3/4.

I've owned the car 4 years and it's always been like this.

Cooling system is fine. I've had it checked.

Temps run in the low 80s.

Never loses coolant. It's just that the gauge reads 3/4 or nothing.

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I have done a number of RB25DET conversions in R32's and I have to use the original RB20 sender to get a correct reading as the resistance profile of the RB25 unit is different. I would suggest replacing the the RB20 item with the original CA or SR item as this obviously has the correct resistance characteristics for the factory gauge.

Cheers

Why are they obviously the correct resistance for the r32 gauge?

Have you tried the CA or SR sensor in an rb20?

Do they screw straight in?

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The gauge in the R32's and the sender unit in the Rb20's are designed to operate together. If you install another motor in your silvia/180sx, you should try and retain the original sender if the orignal cluster is being retained. I know the sender units from the RB25 and Rb20 have the same mounting details as it is simply a matter of removing the RB25 item and screwing in the original RB20 unit. I can't comment specifically on the compatability of the CA or SR temp senders but I wouldn't be at all surprised if they simply screw into place.

Hope this helps

Cheers

Why are they obviously the correct resistance for the r32 gauge?

Have you tried the CA or SR sensor in an rb20?

Do they screw straight in?

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The gauge in the R32's and the sender unit in the Rb20's are designed to operate together. If you install another motor in your silvia/180sx, you should try and retain the original sender if the orignal cluster is being retained. I know the sender units from the RB25 and Rb20 have the same mounting details as it is simply a matter of removing the RB25 item and screwing in the original RB20 unit. I can't comment specifically on the compatability of the CA or SR temp senders but I wouldn't be at all surprised if they simply screw into place.

Hope this helps

Cheers

Sorry, there seems to be some confusion here.

My car is a factory r32 with rb20 so I'm not sure why we are talking about silvias at all.

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Just went and tested mine. Now this is a R32 with a rb25det transplant - I don't recall if I had to swap in the RB20 sender or not. But the gauge works perfectly.

Anyway, mine measures 640 ohms to earth, dead cold.

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Just went and tested mine. Now this is a R32 with a rb25det transplant - I don't recall if I had to swap in the RB20 sender or not. But the gauge works perfectly.

Anyway, mine measures 640 ohms to earth, dead cold.

That would be within manufacturers tolerance of my rb20 sensor (651 ohms cold) so yours was probably swapped to rb20 as others have said is necessary for the rb25 in r32s.

I found the thermo couple sensor for my multimeter so I pulled the temp.sensor from my spare motor and set it up in a pot of boiling water and logged the ohms as it cooled.

deg.C ohms

100 = 25

90 = 35

80 = 49

70 = 55

60 = 72

50 = 100

40 = 193

30 = 257

20 = 580

This seems to be pretty right and from what I can tell is the same as the one in my car.

By these figures my original measurement of 56 0hms at operating temperature means my car is running at about

71 degC so I guess the high reading is coming from the gauge itself.

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