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post #1 of (permalink) Old 11-20-2007, 06:13 AM Thread Starter
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Where is the needle of your temperature gauge?

Hi all,

Just wanted to know where the needle on your temperature gauges on your CJs is? Close to cool and not reaching the green marking or in the middle or even further? Reason i'm asking: after flushing my coolant system and replacing the thermostat, my needle does not stay very close to cool any longer but rather soon jumps to the middle of the gauge (even if the engine is quite cold and the thermostat hasn't opened) Maybe this is the way it should be and it wasn't the last ten years because the coolant system was blocked some way?
Just for explanation my fuel gauge doesn't work (i have heard rumors, this could affect the reading of the temperature gauge as well) but this didn't seem to have an effect on the temperature before i flushed. I have the 151-Gm-4-Banger.

Thanks in advance

momo
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post #2 of (permalink) Old 11-20-2007, 07:44 AM
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My best guess is that your old thermostat was not closing completely, which is the most common failure mode. That made the engine take longer to warm up, and under some conditions kept it from ever getting to proper operating temperature.

Any time you have questions about your cooling system's function, the first thing you should do is start the engione cold with the radiator cap off. Within a few minutes you should begin to see a flow of water in the top of the radiator. Then stick a thermometer into the flow as close to the top hose as possible and read the temperature. Before too much longer it should get to within ten degrees or so of the thermostat setting. For your Jeep that should probably be 195 or higher.

On older Jeeps there's a voltage regulator built into, I think, the temperature gauge. It must be functioning properly for the temp or fuel gauge to function properly. On new Jeeps that's probably handled by the computer.

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post #3 of (permalink) Old 11-20-2007, 08:16 AM
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Another thing to keep in mind is that a stock temp gauge isn't that acurate. And it doesn't need to be. Whether the engine is "cool" or "hot" doesn't matter.

What you want is to know where your engine normally lives. Keeping an eye on the temp gauge on a regular basis will give you a comfort level. Any extreme variation will be easily noted.

Just like you are experiencing now........ some thing out of the norm......

Are you experiencing any issues other than the gauge isn't where it used to be?

If the engine isn't running hot, over heating, or having perfomance issues, I'd say the old thermostat was bad. You are seeing the results of your work, the engine is back to operating temps.

The gauge is just one part of diagnosing a problem. And some times they are the root of the problem. Just double check the information they are giving you.
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post #4 of (permalink) Old 11-20-2007, 08:39 AM
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IMHO, it does matter where your gauges read. As has been stated, you'll get an idea where "normal" is at when everything is functional. Then, you just have to keep it there. The gauges help tell you what state you're engine is in... and that's important. Me, I taught my kids to look at gauges about every 5 minutes as they drive. If you can catch a problem early, it avoids expensive repairs later. Put out the smoke and there's no need to put out the fire.

In this case, did you make sure there's no air bubble in the engine, and it's full of coolant? Me, I pour coolant into the thermostat hole in the block and then install the thermostat. I make sure the thermostat has a burp hole in it's rim t bleed off any trapped air. I usually have cut the heater hoses and installed a back flush kit. That way, at any time I can burp the system by loosening the hose bib cap on the back flush kit.

When all's said and done, if you can't trust your gauges, fix them till you can. If you don't have schematics for the gauges, let us know, and you'll likely get a set by the end of the day via email from someone. It is not hard, and you'll be doing yourself and your Jeep a favor. It just isn't a good idea to drive blind. They don't call them "idiot lights" for nothing....
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post #5 of (permalink) Old 11-20-2007, 10:20 AM Thread Starter
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I could need the gauge schematics for sure. If someone could email this t to me i would be very grateful. An about the air bubble in the coolant system: I'v been driving on the highway for almost one hour, unlike in brake sytems, it should have vanished by now, or am i wrong?

Thanks momo
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post #6 of (permalink) Old 11-20-2007, 10:25 AM
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Yes, it should have cleared by now. If coolant is circulating at about the right temperature, everything should be fine. Just check the level frequently for the next few drives.

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post #7 of (permalink) Old 11-20-2007, 12:02 PM
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I guess my point was that the gauge is just a measuring device. It's not important if your gauge says the coolant is 180 degrees when it's actually 185 degrees. There's going to be a variation with each gauge and vehicle.

The main thing is that you note it's position. Day to day, the gauge shouldn't venture out of it's "normal" range.

It's just as important that you double check the gauge. If I'm reading HOT, and the engine isn't gurgling over, and spewing coolant all over, then I have to realize that the gauge isn't accurate. And to LEVE's point, needs to be fixed.

BUT, if the gauge reads CONSISTANTLY hot, and my engine is performing fine, then it's still a decent gauge. It's not "right", and it needs to be corrected, but you can still use it to keep an eye on things.
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post #8 of (permalink) Old 11-20-2007, 01:52 PM
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I checked the calibration on mine and with a 195 deg t-stat...once it opens, the needle parks right on the mark between cool and green.

Calibrate you say? Well, you don't really adjust it, but it's easy to check. The best way is to remove the sending unit, connect the signal wire to the top, connect a wire to the body and ground this to the engine block....you want to wrap the bare end of the wire a few times around the threaded part of the sending unit body. You then dunk this into a boiling pot of water. if the water is boiling or just boiled, it is going to be about 212 deg +/- a deg or so at sea level (subtract apx 2 deg for each 1000' of altitude...5000' = 203.2 deg). Turn on your ignition and see where your needle is. That is your calibration point.

Now..about your gauge....I believe there is an effect on the temp gauge if the gas gauge is not working correctly....there is a link somewhere that explains it...but I don't have it off hand.

BTW...with a properly sealed system (16PSI), your water should not boil until the temp reaches around 241 deg. Once the water starts to boil your in trouble....steam has only a fraction of the energy moving ability as water.

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Last edited by JeepDawg; 11-20-2007 at 02:00 PM.
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post #9 of (permalink) Old 11-20-2007, 04:39 PM
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Try this Link
http://www.autozone.com/servlet/UiBr...3d801d766f.jsp

1986 stock CJ7 rebuilt 4.2L 258 more to come
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post #10 of (permalink) Old 11-20-2007, 05:17 PM
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Mine read 1/3rd of the way up from the left at full temp.(198-205) But that was a long time ago. Good after market gauges do such a better job.

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