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rundwark

How complex are the stock temp and oil pressure gauges?

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Hey all, I tried searching for more details on the gauges our cars came with but couldn't find anything conclusive.

 

The water temp and oil pressure gauges in my '73 240Z started slowly waving back and forth today: 

 

At some point while driving, they were both stuck close to the low end of their scales. All the other gauges are unaffected.

 

Does anyone know whether the water temp/oil pressure combined unit has a built-in voltage regulator (like the 510's one does, see: http://community.ratsun.net/topic/54598-bad-gauge-cluster-voltage-regulator-easy-2-fix/) that might be failing? Or are they just simpler than that and am I more likely looking at a bad ground connection or something like that?

 

The car's alternator died on me recently and I had to drive it for quite a while off of the battery alone, it must've run on 10V or maybe even less by the time I got to a safe parking spot. This made me think the gauge acting up might not be a coincidence, there might be something a little more sophisticated in there that got damaged by a brownout… Anyone ever open one of these up and remember what's in there?

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It's a bimetal strip. There isn't any type of regulator inside. If your battery voltage isn't consistent, it would do this. Those gauges don't have much in them, just a wire wrapped bimetal strip that heats up and bends when current is passed through it. If the source voltage changes, then the current will change. Check your voltages with a multimeter.

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Sweet, thanks for the reply Winston!

 

I checked voltage and it's very consistent while the car is running. Also there's no obvious correlation between slight fluctuations in voltage and gauge bounces. Sounds like it's most likely a bad connection then.

 

Good news, this means I have a reasonable shot at getting them to work again before a track day next weekend.

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Where's the overvoltage protection in the pic? Is it the secondary white insulated wire spool that sits to the right of the one around the back of the needle?

 

At this point I'm just curious :)

 

Looking at that picture (I failed to extract my gauges this week so that's what I got) the elegant simplicity of these old-school electronics is lovely. As much as I'm tempted to rip it all out sometimes and replace it with something solid-state, modern and more precise. It's pretty impressive to see this stuff last for 40 years and somehow I don't think any of my Arduino's are gonna make it for that long…

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Its the second spool of wire to the right of the oil gauge. Although they are simple, they are not that accurate. I have my Megasquirt controlling the temp gauge through the RB25 temp sensor. It has a dead spot like a newer gauge that sits in the middle during normal operating temps. Works quite well, but it does move around a little due to changing temps in the cabin. 

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I think that the later service manuals might mention that if there's a problem it could be a bad voltage regulator.  Think I've seen it in the 280Z FSM's.  If both needles go wacky at the same time it's likely that, you'd think.

 

Picture from 1973 FSM.

 

 

post-8864-0-56341800-1479525272_thumb.png

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