Public service message: set a low voltage alarm!

In case your alternator decides to depart from its bracket, which is apparently a thing, you also lose the single belt that drives the water pump. Mine let go, and while I was getting intermittent high temp warnings, it was bouncing between 180 (normal) and 226, so I thought it was a bad sensor. My voltage alarm was set at 12.4 (which was just below what the old generator would maintain at idle), but my battery stayed above 12.6... so I ran 6 laps with no water pump. 3 weekend engine going back to Enterprises for rebuild. Looking at data, the alternator is consistently above 13.5 volts... so set your alarm somewhere around 13. Would have saved me.

Where is your water temp sensor? If in the motor, I would have thought that the lack of circulation would result in such high water temps that you'd get an alarm for that?

-Mark

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Originally Posted by lowside67

Where is your water temp sensor? If in the motor, I would have thought that the lack of circulation would result in such high water temps that you'd get an alarm for that?
-Mark

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It's at the back of the engine, in an assembly with a bleed line and the pipe for the radiator hose/tube.
From the first increase in temperature (from 183 to 184), which I assume is within a couple seconds of when the alternator broke off, it took 8 seconds for the voltage to drop below 14.0.
Within another 10 seconds temp reached 200 and I got my first alarm (and voltage was 13.1). So, if my alarms were set for 200 and 13.2, I could have known to shut off after 18 seconds.
Another 10 seconds, temp was 226 and voltage 13.0.
Curiously, the temp never recorded higher than 226... not sure if that's a function of the sensor range, or the PE3 calibration limits, or what. I will look into that, as well. My car normally runs 180-183 coolant temp.
Also curiously, over the next few laps, the temp reading would bounce between 180 and 226. Maybe that's a function of the sensor being splashed vs steam, or the system burping. Not sure, but I think if the sensor isn't immersed, it doesn't function properly. Unfortunately, this tricked me into thinking it was a bad sensor, loose wire, etc.
Oil temp started to rise also, from 230-ish, up to 287 6 laps later. I guess I should set an oil temp alarm, as well.

Could you run a coolant pressure sensor? Or just a dummy light?

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Originally Posted by Mike B

Could you run a coolant pressure sensor? Or just a dummy light?

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Not sure if there's a port available for pressure. Knowing what I know now, alarm for high temp and low voltage and at the correct limits serves the same function. Having this type of detail from SCCA-E would have been nice. On many SRF3 cars, there is an rpm sensor on the alternator, for the same reason. Guess I could have added something like that, as well.

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Originally Posted by Mike B

Could you run a coolant pressure sensor? Or just a dummy light?

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This is what I run. 4lb pressure switch with light. But it won’t tell you if the water pump goes since system will hold pressure until it cools.

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Originally Posted by mikey

This is what I run. 4lb pressure switch with light. But it won’t tell you if the water pump goes since system will hold pressure until it cools.

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Yeah, I've always thought the WP pressure sensor was for something like a holed radiator or loose hose or clamp.

Good info and thank you for sharing.

A friend also ignored a water temp gauge they thought was faulty, several thousand$ later they were back racing.

The takeaway I get from this is don't ignore gauges (we put them there for a reason). If we think they're faulty, wiring or sensor on the fritz pull off/in and check it out back in the paddock. Unless you're fighting for, or in the lead at the RunOffs on the last lap, then feel free to ignore all gauges and funny sounds. Or if you're just having so much fun and engine rebuilds aren't a major concern feel free to carry on.

If the water is leaking your temp gauge will let you know as it will fluctuate a bunch while you are driving, same is true if water stops moving in the system. Good reason to glance at the gauges and any needle that is moving around is certainly a warning sign meaning you already have a warning device on board!

I think what threw me is that the temperature stopped at 226°. That is not inordinately high for a glycol/water automotive system with a pressure cap. Then, it was bouncing between 226 and 180 (which is the normal temp). So, frankly, I didn't understand the messages I was getting. Like I wrote before, if I'd seen temp and voltage warnings I'd have stopped. If I saw 240° or 250°, I would have stopped.

Lap 12 data (water temp is the bottom signal):
https://www.apexspeed.com/forums/att...id=93348&stc=1

Lap 13 data:
https://www.apexspeed.com/forums/att...id=93347&stc=1

So did the bracket on the alternator brake ? Or did it loosen up? Any photos of the bracket if it did brake?

Based on how the temp graph gets 'clipped' at 226, I'd say there is something that is artificially limiting your data to that maximum - either logger config, or sensor calibration.

I believe the lower, pivot bolt broke first. There appears to be some fretting on the mounting face between the alternator and the lower machined mount. The upper machined mount then broke at the forward bolt hole.
Attachment 93349

Both the PE3 and CDS systems do not appear to limit temp to 226 - they should read up to 240. Possibly a bad sensor, or a bad sensor calibration.