**EDIT**...I found out something very interesting today. (READ POST #9)

I'm a little confused about which lines on the temp gauge are for what temperature. (On my '81) Obviously the first "Thick" line is the 100 degree mark. Then there's a thin line before the next "Thick" one.

What temperature is that second thick line? Is THAT the 200 degree mark or is it maybe a 180 or 190 mark? (I'm running a 180 stat) It looks to me like the 200 degree mark is the next thin line after the 2nd thick one. (12:00 position - 200 sits directly below that line)

I ask because when I'm in town sitting at stop lights in 85 degree weather, my needle stays on that second thick line constantly. The "Only" time my needle ever moves above that mark is when I'm on the freeway. Then it moves up between the 2nd thick line and next thin line after that. (11:30 postion)

Yes, I said that right,.......when I'm sitting in stop & go traffic in HOT weather, my gauge comes down and stays on that 2nd thick line. It only goes up about the thickness of the needle when I keep the RPM's up around 3k and higher. I'm running a 3000 stall converter, and at 65-68 mph my tach reads 2800 rpm. At 75 mph I'm right at 3000 rpm......which is when it starts moving up to the 11:30 position.

 

Dash gauges are not marked with numbers because they vary a lot.

Why don't you get a thermometer to check the temps against the dash gauge and assess your gauge's calibration.

You could also borrow an infra-red thermometer for spot checks around the block to see if there are any issues with cooling jackets in the block.

It does seem very odd that temps rise whilst you are cruising at speed.
Have you got the proper lower return hose (with internal coil spring)from the radiator? Maybe your return hose is collapsing reducing coolant return volume.

cheers
tom

 

Yes, I have the correct lower coil spring hose. And don't you mean: "Dash gauges are not marked with ALL the numbers", because I have 3 different numbers on mine. (100, 200, and 260)

My car doesn't over heat, I simply want to know which lines on the gauge are for which temperature reading. I wouldn't expect a gauge from a 74 to be the same as mine, so I hoped that someone with a similar gauge would be able to answer that Bold Highlighted Question.

It's already in the upper 80's here and my car has never run hot enough to even make it to the 12:00 position,......which I'm still thinking is the 200 mark on the gauge.

Thanks for the reply though Tom!!!

EDIT.... I actually just found the thread below in the Search engine. (It didn't show up the way I worded it earlier)
http://forums.corvetteforum.com/show...the+Temp+gauge

 

the first heavy line is 100. then there is a smaller line representing 150 . the second heavy line right near the 2 is 200. .from there they go up in increments of 15 . if you needle ever goes past vertical i would say its a good time to shut down. any more than that and your engine is getting damaged. i run an autometer mechanical gauge to be more accurate.

i am also running a 3000 stall and it is normal for your temp to rise higher than what it would at slow speeds. on hiway speeds my temp sits at 190. in slow moving traffic 185 and with thermo fan on even lower. this is because your engine is working hard at 3000rpm on highway and your water pump is cycling the water at high rate. it has less radiator time so runs a lil warmer.

 

The C3 water temp gauge is merely an "indicator" of temperature. The accuracy of the gauge, sender, etc. is poor, at best. The intent of that gauge design is to provide an analog indication that the engine is NOT heating up properly or that it is OVERHEATING, not to provide the actual engine operating temperature. If you need that kind of info [not sure why you would], buy a precision thermocouple and calibrated gauge. Then you only have to decide where to place the thermocouple on the engine....because anywhere you place it will give different readings than for any other location on the engine.

 

Ok, that makes sence. My engine's actually gonna run a little hotter than most of yours anyways since I have a small block 400. (Not by much though) I bought a 16" electric fan for it, although I haven't thrown it on yet. Hopefully that will get it down into the 190 range.

Here's another question though,...nobody sits with their head directly over the e-brake console, so they're looking at the gauge from a slight angle. If I move my head over and look at the gauge straight on, that's about the thickness of the needle. Nevermind, that doesn't matter.......I'm going to go buy a mechanical gauge for it today.......that should answer all my questions.

 

i asked this awhile ago myself an numerous folks confirmed that the skinny mark at 12:00 o'clock is 200 degrees. I always though it was the thick one to the left too, but everyone told me different. I think if the needle is vertical, thats 200 degrees.

 

Have tested several C3 gauges and with the correct sending unit, they are all pretty close to this.
To get them to go over the tstat temp, I put cardboard against the radiator. Measured with a pyrometer.

 

Ok, I decided to go out there today since it was 96* in the shade. I started my car up with the Radiator cap off and let it idle for 15 straight minutes. At no time did the coolant ever start flowing even when my gauge was reading 200*.

I have a 180 tstat in there with a hole drilled in it. My first thought was that my tstat was bad until I went in the house and grabbed the Thermometer you push into a Turkey when cooking. (I figured it couldn't hurt)

So I went out and stuck the 6" probe down inside my radiator.........Low and behold my temperature was holding steady at 170* for another 10 minutes. (Yet the whole time my gauge was reading 200*)

Here's the proof........



96 degrees outside while testing!!!




Can't see the fan blades because my engine is running




Here's my gauge reading 200*...(and NO, my oil temp gauge is not hooked up)




Here's my tester stuck down in the radiator holding steady at 170*




After idling for 25 minutes in 96* it's still not flowing because it hasn't reached 180* yet





I know why my guage is off now,......I forgot about the fact I'm running 1969-70 Camaro/Corvette 186 casting heads. It doesn't have the correct ohms for the temp sender.

So once again, I definitely need to go buy a mechanical gauge!!!

.

 

If coolant is not flowing thru the radiator, as you stated, then the tstat is not open and you are not measuring the engine temp, just the cooler coolant temp in the radiator from the coolant being circulated thru the hole drilled in the tstat.

Your stock gauge is reading the engine temp and it should be way over 170°, as it shows, after 25 minutes, especially with ambient temps of 96°.

Do your test again after a drive and your tstat has opened with hot coolant running thru it. That will give you a more true reading of the stock gauge accuracy.

Looks like your tstat is a little slow like you first suspected.

 

Yup, that certainly worked. The gauge is still off by quite a bit though. I took it for a 60 mile drive with the ambient temp of 100*.

When I got home I pulled the rad cap off and watched as the coolant was flowing steady. I went inside and grabbed the tester again and stuck it down in there, and it came up to 185* this time. (and it stayed there) As you can see from the gauge in the first pic, it shows it as being about 210*.

I was actually worried last night the more I started thinking about it, .........I figured if it wasn't circulating through the radiator and holding steady at 170*, well that isn't good for it either. It needs to circulate and run hotter than that to burn the fuel properly.

So, thanks for the suggestion. I'm gonna go buy a mechanical gauge for it as soon as I finish this post!

Here's what it looks like today...............

 

I think you are confused about what marks on the gauge are which temps. The line at 12:00 (vetrical) is about 200F....not the one to the left of it (11:00). From what I've seen on your pics, you are running around 180F. Just note where it runs and quit worrying about it...as long as it keeps running in the same vicinity.

 

Where the hell do you get off telling me what I should and shouldn't do? DO NOT tell me to "quit worrying" about my own car,.. ...I'm trying to make sure I protect my investment. I just spent a ton of money on this brand new motor and only have about 400 miles on it. The temperature here is VERY hot and I don't wish to take any chances of overheating it.

As I said I was going to do twice now, I've gone and bought a mechanical gauge for it, so now I can watch a much more actual reading of how hot it's really running.

If I remember correctly, this is a website where we can all come to ask questions about things that we're unsure of. What you just did was insulted me on a personal level by insinuating that I was asking too many questions.

Read my last post,......it clearly states that I realized what the problem was and also shows how I intended to resolve it. Besides, the truth of the matter is, I was never worried about it in any way, shape or form. Not once did my car overheat or even smell hot,.....I was simply asking a question about which marks on the factory gauge represented which temperature.

**EDIT**.....Oh yeah, what makes you so sure that second thick hash mark isn't the 200 reading??? Why is it that there are only 3 thick hash marks on the gauge, and there's also ONLY 3 numeric numbers. (3 marks, 3 numbers) Unless you can prove to me with 100% certainty that that the straight up 12:00 position mark is in FACT the 200* temp reading, then your statement is nothing more than just your own personal guess!!!

Hmmm, something tells me that after this, I'm probably going to get a factual answer from somebody who knows forsure. (But then again, it won't really matter anyway. I'll have that mechanical gauge installed in the next hour)

 

straight up on my 72 is 202 degrees ( measured with a thermocouple) @ t-stat end of rad hose. also don't assume a mechanical guage is bullet proof,some of those are off, i've had a few over the years . also most guages are only accurate in the middle 30-40% or the range,extreme ends are sometimes off , sometimes by a lot.bottom line,if you REALLY want to know the temp, get a calibrated guage of somekind.

 

What you really need is the correct sending unit for your gauge. Then you won't have to add another gauge and try to mount it somewhere so it doesn't look like a kludge. GM used different sending unit gauge combinations over the years. If you try to mix and match, you'll end up with an incorrect reading gauge. Easy fix: Get the correct '81 sending unit. You might have to use an adapter if the correct sending unit is smaller than the hole in the head.

Cheers,
Pete

 

i think your wrong 7t1. on your car straight up and down might be 200 but str8upchevy stated he has an 81 and they have different gauge markings to yours . u can even see that in the two earlier pictures in this post by myself and noonie.on the 81 the heavy line to the left of vertical is 200. i like noonie,s comments and i agree with him you should get a new thermostat.after 25 minutes it should definatly be up to temp with thermostat open. also its not really good to leave them idle for that long. you can glaze your bores.

7t1 what you said about it running in the same vicinity and quit worrying is B.S.
so if my car runs on 240 (or same vicinity ) thats ok and quit worrying...i dont think so.

str8upchevy you seem to have the problem sorted and i think running a more accurate gauge is an excellent idea.not totally necessary but i do it and wouldnt have it any other way for the two more important gauges. oil pressure and water temp.

 

The poster already measured the actual temperature and knows it is around 180F at the present needle position. All I said was, that needle position is all he really needs to monitor....watching for some significant change either way from that might indicate a problem. Does that suggestion indicate that I'm "telling him what to do"?.....only if he's paranoid.

 

I'm with you on this one 7t1.
There was NO malicious intent on your behalf.
str8upchevy must have other issues to sort out.

Once you know that the actual temp IS OK, and you know where the actual temp sits on the guage.... then there's no problem.

But if str8upchevy likes to spend money to make himself feel better, so be it.

And by the way str8upchevy..... with a short wick like yours, I wish you all the best with future advice. You'll learn quick that jumping to incorrect conclusions and jumping at posters who try to provide feedback will net you less responses.

ciao

 

NO, what you just said above had nothing to do with my reply. (You just stated everything except the two reasons for my responce) I responded to you telling me I was confused (or wrong) and that I need to "Quit Worrying" about it and just drive it the way it is. I would much rather read a gauge that's correct rather than one that's off by 25 degrees. I obviously proved by the pictures that my factory gauge is not even close to being accurate. So you think I should continue to trust a gauge that I've proven to be inacurate and "HOPE" that it continues to keep giving me "in the vacinity readings"??? Sorry, but I don't take chances like that with my cars. I have much more "Pride of ownership" than to be that foolish........if you feel comfortable doing something like that on your own vehicle, well good luck.

The thing is, when "noonie" came up with a simple easy suggestion for me to try, I went ahead and tried it and realized exactly what the problem and solution for it was. "END OF STORY"!!! Then you come along and tell me that I'm confused about the marks (Without ANY PROOF) and then told me to "quit worrying" about it like I was some little whiner going on and on about something that didn't really matter. If I'm not mistaken, this is in fact the place to ask questions about something you're unsure of. As I said before, this is a brand new high dollar motor I just installed and wanted to make sure I was getting an acurate reading of the temperature so as not to harm my investment. Is that so wrong to do???

And I don't give a Rats A$$ if "OzzyTom" thinks your reply was done without malice, and thinks I have issues or whatever.. ...I just finished flushing his opinion down the toilet about an hour after I finished my dinner.

My gauge is now installed and I have the correct temp readings, (within reason) therefore I see the original subject closed.
So, if you 7T1 (or even you "OzzyTom") wish to continue discussing this rediculous matter, by all means lets take it to a PM status.

 

str8upchevy - cool down - check your own thermostat setting. The folks here are just trying to help. Doing it via the Internet is not as easy as being there.

FWIW, not having a working oil pressure gauge would worry me a lot more than the absolute (175* vs 195*) accuracy of my temp gauge.