The Dodge Challenger Message Board

HI all - on a SB engine (mine is a mild 360), what should normal operating temp be reading on the rallye gauge? I have had the gauges checked over and have tested 3 sending units. It is reading very cool at normal operating temp, just barely off cold. All the small blocks i have had all seem to read low. Is this a Chrysler thing? The sending units are all different when tested. One was 900ohms cold to 85 ohms in boiling water, the other two were 250 and 180 ohms cold going to 44 and 22 ohms in boiling water. Obviously in an overheat situation it should go top zero ohms which would be full scale hot on the gauge. But i would think that normal operating temp, the gauge should read about the middle. Thanks

ByTheWay, the sending unit that was in it was the lowest ohms, so it should read the highest...

For what it's worth, mine has always read in the lower range. I have replaced thermostats many times to check and they had no bearing. Just having a feel for under-hood temps, it seems 180 is about where she runs.

Oh, bye the way, there has been recent conversation about the amp gauge by-pass effect on the the stock reading. The low "discharge" in the picture is normal in this particular situation. It does move due to a change in idle and when accessories, such as the headlights on/off. After a while I learned how to judge the scale for charge in my car.

Interesting post. I am curious for an answer because mine reads the same as yours. It just barely moves off of the cold reading.

Thanks for replies fellows, Jon, love that picture! You took that shot in First gear at 14 mph, am i right? Very nice, i put it in my collection. Yes, my temp gauge reads exactly that - ! a little annoying. You have got great oil pressure, mine is not that high at normal temp, a bit above halfway. Also have not seen that colour dash pad - is the whole interior that colour?

Bob, looks like yours is the same too. It must be the way the gauge is calibrated then. At normal operating temp the sending unit will give a certain resistance, obviously it is not letting quite enough voltage through to put the needle in the centre. I took off the send wire and with Ign on, earthed it to the body. The damped needle moved smoothly right up past full. Steve.

Yes, that picture I took slowly chugging up out dirt road. It was during winter with temps around 60 degrees. Even in the summer it reads about the same. I have a newer 3 core radiator with a flex fan and she never hints at overheating. Only heat related problem is some fuel boiling after I shut it down, probably the heat crossover in the manifold.

Oil pressure is reads high due to the Mellings oil pump I believe.

Possibly you/we are losing continuity somewhere between the sender and gauge. Have you tried jumping a wire directly from the sender bypassing the bulkhead connector in normal operating conditions? Not sure how the in dash voltage regulator plays in so maybe not a good idea without someone else's expert advice.

I know there are places to get the gauges calibrated. It would seem to be a lot of down-time and effort though.

i bought an infrared hand held thermometer ,i use it at the track for brake rotor,caliper temp,etc., i always have wondered the engine temp and have used it alot now since i installed an oil cooler and a trans. cooler,when my dash temp gauge is half way(which is where it normally runs) the infrared unit says at the thermostat is 175 degrees F ,at the back of the engine where the dash temp sender is located it says about 185 degrees F to me when the dash gauge is at half way it is around 180 to 185 f, now i know your cars are different,and the gauges will be different ,but i want to know the actual temp. in numbers,so i really need to install a gauge with numbers so i know what true temp is

Those inferred gauges are cool. The inspector on our job had one to check the temperature of the Asphaltic concrete as it was placed and compacted.

I'm cheap though so maybe using the wife's turkey thermometer in the radiator fill would do the trick. Heck she may not even miss it till November if I'm lucky. Or just clean it up nice and sneak it .....

Jon wrote: Possibly you/we are losing continuity somewhere between the sender and gauge. Have you tried jumping a wire directly from the sender bypassing the bulkhead connector in normal operating conditions? Not sure how the in dash voltage regulator plays in so maybe not a good idea without someone else's expert advice.

I know there are places to get the gauges calibrated. It would seem to be a lot of down-time and effort though.

That's a good thought, i might pull off the sender wire and while its runnning at normal temp, check the resistance. Yes the Voltage limiter does power those gauges, it is dropped to 5V. Battery voltage will fry them. I have just installed a new Solid state (electronic) volt limiter from RTE (DashWorx), not cheap at $50, so i don't want to play around with that! It is a lot of effort to go to, to get the gauge reading like Drew's (lucky you). However i have another rallye instrument cluster, i might take that into my instrument place and have them look at the gauge and see if they can be recal'ed, but i doubt it, without a lot of effort.

BTW, Drew, thanks for those temp numbers. Now i have to convert to degrees Celcius, as Deg F , i have no clue about.

Celcius, as Deg F , i have no clue about, can rune some tests with it in celcius,and i dont do that kind of math but i will run some time this week justso we know, it will be hot here this week so we can really know

175 F = 79.44 C

180 F = 82.22 C

185 F = 85 C

I think the Americans are the only people left in the world that still use that obsolete Fahrenheit scale.

[°C] = ([°F] − 32) × 5⁄9

Thanks Dave! Those numbers are pretty low then, not even near boiling. I can throw some sender units in the saucepan with a thermometer and measure at different temps.

As another addition - i had a newly rebuilt 340 in my (oz) Charger and when i first started driving it, it was running way hot and right up the scale on the gauge. In the first 5min of running it fried off the paint from the extractors. It was hot weathr too and i was getting agitated watching the temp gauge go right up on my new motor, in city stop-go-stop traffic.

I nearly cooked that bastard - finally found it was an inoperative thermo fan hub. I put a good one in and it ran cool. And i found that normal operating temp then was very low on the gauge - just out of the blue, in fact. But the motto of this story is that the gauge will use all of its scale when the engine goes hotter than normal, and so i think it is a true indication. When that gauge goes around and past halfway, its time to stop and check things out.

Steve

When that gauge goes around and past halfway, yes thats where i like it mine does go hotter depending on what im doing, i have run it at about 3/4 on the gauge on the track for quite a long time with out boil over so yea half way up the gauge is the safe area , im like you i get a little hot under the collar in stop and go traffic and then the engine starts to creep up and yea i know oh yea sorry we yanks are still in the cave man era on measuring stuff

drewcrane wrote:oh yea sorry we yanks are still in the cave man era on measuring stuff

Well it was the fault of us British probably. It was probably us that started you off on it.

There have been a few cock-ups in the space industry due to you guys not using metric. A lot of the satellite techs are European.
Remeber the cock-up with the Hubble space telescope being out of focus? Due to the American techs talking a cm measurement and thinking it was inches?
We lost a Mars probe due to the same thing. Ooops!

[quote=

I think the Americans are the only people left in the world that still use that obsolete Fahrenheit. [/quote]
I resemble this remark!

I work for an aerospace company, and whenever we get a blueprint in from a foreign company such as SNECMA, Rolls-Royce, Honeywell, it all has to be converted from metric to inches. All of our inspection equipment, indicators, and such are inch, but the customers require part results in MM, of course.

So we go from metric to inches to metric again while producing and inspecting the part. Unbelievable headache, and the source of endless confusion.

It is rather funny to get a fixture from a toolmaker who forgot to check the units the drawing is in. They wheel in something on a cart that was supposed to be the size of a slice of bread!

Well it was the fault of us British probably i can go with that i had to start some where

The government has tried to get us yanks to go metric since I was a kid.

It took Jap dirt bikes to get some of the conversion across to me. It will take at least another generation or so to get the job done for the masses.

Bye the way it was only 32c today. In the middle of summer, can ya.

gday steve the variation may be in the sender units in your cars as i have just done an engine swap in my ute & the original motor the temp gauge ran 1/2 way on the gauge & the new motor reads very low , the new motor already had a temp sender so i left that 1 in it also it had no thermostat so swapped that for the 1 from the original motor therefore it should be running at the same temp as with the old engine no other changes were made
cheers ian

drewcrane wrote:When that gauge goes around and past halfway, yes thats where i like it mine does go hotter depending on what im doing, i have run it at about 3/4 on the gauge on the track for quite a long time with out boil over so yea half way up the gauge is the safe area

Drew i think yours is reading correctly, well in the more desireable area anyway. So 3/4 on yours is getting warmish, and would be similar to ours going to half i suppose. It would be interesting and helpful for me (next time you are "in that area") to see what effect putting in a couple of different sending units would be on the reading. If the gauge drops lower, then it would be that particular sender you have which has different thermal-resistance range. Then again, you have a big block don't you...so swapping them around might not be as easy as the SB's.

ianandjess wrote:gday steve the variation may be in the sender units in your cars as i have just done an engine swap in my ute & the original motor the temp gauge ran 1/2 way on the gauge & the new motor reads very low , the new motor already had a temp sender so i left that 1 in it also it had no thermostat so swapped that for the 1 from the original motor therefore it should be running at the same temp as with the old engine no other changes were made
cheers ian

hi ian, yes i assumed that too, but as i mentioned i swapped in different sender units and all the same. The one that was in it, had the lowest resistance in boiling water, so theoretically, that one should let the most voltage through and read the highest. BUt now that Dave has said what the normal operating temp is in deg C, i can measure the resistance at that temp and see what they give. You're talking about your Slant 6 too arn't you? Maybe they have inherent different warming characteristics or sender placement? MIne is screwed into an aluminium manifold, which might give a cooler reading

at this altitude im at water boils at a lower temp,and yes i di have a big block and my wifes cuda has one too.they read a little different as in her car runs/reads cooler about half way up,min under normal driving conditions reads about half way, however if on the hiway tach reads 3800 rpms ,i also use an electric fan i can get it to read about 1/4 the way up the gauge a little cooler,