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Old 11-23-2019, 04:08 AM   #1
oemoilleaks
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Default R-Sport cluster's temp gauge question

Can anyone tell me what the volt limit is for an r-sport cluster temp gauge? (or better yet, post a picture of the back of one, or link to a part number?)

Some Context:

This is going to sound silly but I have been using an r-sport temp gauge as an auxiliary oil temp gauge in my 140.

I run it with a sender in the drain plug which hasn't been an issue until this very day. Originally I had a 150ºC VDO sender in there but the gauge would always read above 120ºC. So I said to hell with the numbers and put in a 200ºC VDO sender figuring that at least I would see some upward movement if it got any hotter. I never saw it go above the 1/2 way until today.

I'm just trying to figure out the cause for the sudden sensitivity of the gauge.
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Old 11-23-2019, 05:09 AM   #2
John242Ti
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Pegged will be battery voltage. The sender is a ground contact. When the temperature is cold, there's no ground. As it heats up, the resistance goes down, causing the needle to rise. The water temp gauges are rated up to 125 deg C. What I would do is hunt for an oil temp gauge, either a Volvo-branded one, or the equivalent VDO cockpit/vision gauge. Use that with a 150 deg C sender. Then things will work properly, and you'll actually know what the temperature of the oil is. Better than trying to use a VDO Rallye water temp gauge as an oil temp gauge with a sender that's rated for an extremely high temperature.
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Old 11-24-2019, 09:52 PM   #3
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Pegged will be battery voltage. The sender is a ground contact. When the temperature is cold, there's no ground. As it heats up, the resistance goes down, causing the needle to rise. The water temp gauges are rated up to 125 deg C. What I would do is hunt for an oil temp gauge, either a Volvo-branded one, or the equivalent VDO cockpit/vision gauge. Use that with a 150 deg C sender. Then things will work properly, and you'll actually know what the temperature of the oil is. Better than trying to use a VDO Rallye water temp gauge as an oil temp gauge with a sender that's rated for an extremely high temperature.
To clarify, it didn't just go straight to pegged. It rose steadily, and even after the car cooled would rise again quickly.

I'm planning on switching out the sender on the next oil change and trying to run a temp sender on a 'T' from the oil pressure sender port.

The theory with that is that it will take oil temp from a place with flow as opposed to the bottom of a baffled oil pan, where we think there might just be a layer of oil that's never getting sucked up into the pump.

Last edited by oemoilleaks; 11-25-2019 at 12:30 AM..
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Old 11-25-2019, 02:47 PM   #4
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Originally Posted by oemoilleaks View Post
To clarify, it didn't just go straight to pegged. It rose steadily, and even after the car cooled would rise again quickly.
More clarity: Does it rise steadily with key on engine stalled? Or can I assume it is a steady increase as you drive along over a period of ten or twenty minutes?

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Originally Posted by oemoilleaks View Post
I'm planning on switching out the sender on the next oil change and trying to run a temp sender on a 'T' from the oil pressure sender port.
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I have no idea what I'm doing.


Neither do I, but it is fun.

I wouldn't expect any flow at all at the pressure sender. Just enough to move its tiny diaphragm, and that's done. Gotta be more mixing in pan slosh despite the air cooling. What is the purpose of taking oil temp measurements in this particular engine? Track? Do racers ever use a thermistor dipstick?
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Old 11-25-2019, 07:34 PM   #5
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More clarity: Does it rise steadily with key on engine stalled? Or can I assume it is a steady increase as you drive along over a period of ten or twenty minutes?
Depends. If the engine is cold, the gauge won't rise until the engine is starting to get up to temperature.

If the engine is already warm it'll rise without the engine on. But as the oil cools, the needle will come back down. It's acting like it's reading the oil temperature.

We are talking oil temps simply because I happened to have the gauge hooked up and noticed it spiked. More info = more worries = more problems.
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Old 11-25-2019, 08:07 PM   #6
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Originally Posted by oemoilleaks View Post
Depends. If the engine is cold, the gauge won't rise until the engine is starting to get up to temperature.

If the engine is already warm it'll rise without the engine on. But as the oil cools, the needle will come back down. It's acting like it's reading the oil temperature.

We are talking oil temps simply because I happened to have the gauge hooked up and noticed it spiked. More info = more worries = more problems.
OK, that's clear. The normal failure mode of a temperature sender wouldn't explain that behavior nearly as well as the failure of the gauge voltage stabilizer, especially if it is the old mechanical variety.
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Old 11-26-2019, 02:48 PM   #7
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OK, that's clear. The normal failure mode of a temperature sender wouldn't explain that behavior nearly as well as the failure of the gauge voltage stabilizer, especially if it is the old mechanical variety.
Ah that brings up a good question. Were these gauges (the water temp specifically) meant to run on a voltage stabilizer? If that's the case I think we've found our culprit.

Although, to be fair, in 2+ years of having this setup, it has never once spiked like this.

I have procured a proper oil temp gauge and matching sender from a friend for the purposes of diagnosis and will report back today or tomorrow.
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