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I’m trying to figure out where to mark the warning indicator on my custom gauges for water temp. I tried to figure out what temp the yellow mark started out on my original gauge but then read on some older post that the marks don’t equate to equal number spacing. The sales rep asked me what would be considered a normal higher temp range on a big block and I said I didn’t know.
Their gauges go from 140 to 280 with 195 being in the center. 220 is between 195 and 280. I’m trying to stay close to the original style but would like the yellow warning mark to be useful.
Would 220 be the right place to start for the yellow warning mark?
Are you using a pressurized coolant system and a coolant recovery tank as original or a higher pressure more modern system? Water boils at 212F at sea level, and a 50/50 water/coolant (typically ethylene glycol) boils at around 220F at sea level. When new, C2s used 15 pound radiator caps, meaning that the cooling system was pressurized to prevent the coolant from boiling as long as it stayed under about 250F. If you're going with a higher pressure cap, you'll want to find the boiling points for those higher temps, but it is approximately 2-3F for each pound over 15, but you'll need the entire cooling system rated for higher temperatures and pressures. What did C2 big block temperature gages red line or yellow line at? Do you know what temp your engine tends to run at?
Hi Easy. I have a Dewitt’s 15 psi cap and radiator. No recovery tank as I don’t believe big blocks had them. Here is a pic of my original gauge. Engine hasn’t ran yet but I would think it would run below 220.
I'd make it warn me when things are getting a bit too warm for comfort...220 is a reasonable warning point, 230 is also reasonable. When it gets to 240 I'm ready to park and let it cool down.
But you can make up your own numbers. There are lots of things to consider, besides when the engine will sustain damage from overheating.
Yeah, I don't know about big block cooling systems. But I did look at this from 66-67: https://www.zip-corvette.com/66-67-t...ure-gauge.html which appears to match your faded original. Clearly it's not linear going from 100-210 on one side and from 210 to 250F in the same sweep on the other side, but that would seem to say around 230F is yellow and 250 is red, but I'm not sure that even makes sense. So are you wanting to go with technical 'accuracy' (such as it is?) or visual 'balance' (i.e., what looks good?). Not sure it actually matters technically. Edit: But those are sure some good looking gages, although it appears that they are also not exactly linear.
Hi Easy. I have a Dewitt’s 15 psi cap and radiator. No recovery tank as I don’t believe big blocks had them. Here is a pic of my original gauge. Engine hasn’t ran yet but I would think it would run below 220.
Chris,
With your setup (DeWitt's Radiator and pull fans) you should see normal operating temps between 185*-190*. Just as an historical note, see what the 1967 Owner's Manual said about operating temps.
IIRC, factory installed thermostats were of the 180-195F variety. Seems to me that the engine once warmed up would be in the high 190s or just over 200F range unless hot outside, sitting in traffic, and running lots of accessories (e.g., AC?) if the cooling site was up to snuff?
Clearly, their gauge is not linear with 140 to the midpoint of 195 being 55 degrees and then 195 to pegged at 280 being 85 degrees. Half way between 195 and pegged is about 240 (3/4 mark) and I wouldn’t run the engine beyond that temp. So, at a minimum start the yellow at the half way point between 195 and the 3/4 mark and red at the 3/4 mark. Remember, you have aluminum heads and they don’t like to get as hot as iron heads.
I agree with having the warning zones conservative. I'd want to verify the readings with an IR gun after I get up and running.
You never know what the accuracy of the sensor/gauge is, hopefully better than the OEM replacements are.
My Blueprint 496 stays at my thermostat temp of 180*. I have a Dewitts radiator and an aftermarket 6 blade fan with a thermal clutch.
This may help a little on factory gauge calibrations.
Well maybe not - I thought it described approx temps for the hash marks but it doesn’t.
While it doesn't provide a direct correlation to temps, testing a temperature sensor with an ohmmeter at different known temperatures could result in having a good match between readings and actual engine temps. I'm guessing that the temp circuitry is a simple Wheatstone bridge?
While it doesn't provide a direct correlation to temps, testing a temperature sensor with an ohmmeter at different known temperatures could result in having a good match between readings and actual engine temps. I'm guessing that the temp circuitry is a simple Wheatstone bridge?
Yes, if you assume the ohm reading is a direct, linear relationship to the water temperature and gauge reading, it looks like the hash mark between the 100 reading and the 180/210 mark is not exactly half of the difference, but more like 2/3 of the difference. But between the 180/210 marks and the 240/250 readings, the intermediate hash mark is pretty close to half the difference. Not sure if that is a good assumption on my part as I’m no electrical wizard.
Yes, if you assume the ohm reading is a direct, linear relationship to the water temperature and gauge reading, it looks like the hash mark between the 100 reading and the 180/210 mark is not exactly half of the difference, but more like 2/3 of the difference. But between the 180/210 marks and the 240/250 readings, the intermediate hash mark is pretty close to half the difference. Not sure if that is a good assumption on my part as I’m no electrical wizard.
Okay, since I'm geeking out on this item, I'm all but certain that some smart C2 electrical guy has figured out all about non-linearity, trimming resistance, and resistance matching and has posted it somewhere. I'll see if I can locate it, although it may be more than Elwood the OP cares to know.
Actually, I think it would be interesting to know Easy. I wonder what the difference is between the original senders and the new ones?
I told the guy at Classic Instruments to mark the yellow from 220 to 240 and red from 240 to 280.
Once she is up and running I will compare the dash gauge, the ECU reading and hit it with the IR gun. Of course with my luck they will all read different and put me in an OCD spiral. Lol.
Typically it’s an Easter egg hunt to find a sender that will go much below 100 ohms and as the chart above shows, to go full scale hot it needs to go as low as 50 ohms. But even above 100 ohms they often read higher ohms at lower coolant temps, making owners think their cars are running hotter than they should. (Hope I got that right) There are a few shops that sell resisters to go in line with the gage to calibrate the sender to the gage. Wilcox is(was) one place.
04-09-2024, 11:48 AM
Big Block Running Water Temp Question
