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Old 01-08-2003, 08:20 PM
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Smile Temp. sending unit

After putting a new engine in my 36 Dodge a few years ago I noticed the temp gauge would peg out, then drift back down to 180. Happened about every 50 miles or so but lately it's alot more often. Other than motor nothing has changed, same VDO gauge, sender, and wiring. I checked connections at sender and gauge and both are fine. Sound like a bad sending unit. Thanks for your help.

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Old 01-09-2003, 03:18 AM
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Well the best I could do for now is just give you some generalizations. Most common causee for eratic gauge operation are, air in system (system opened and not burped thoroughly-no overflow tank to keep air out of system,etc.), thermostat not opening up when it should, sender problem. Does this only happen when first warming up and then she runs fine after that? That would sound to me like a sticky t-stat. Does she do this the entire time you are driving? If so is it when you stop for stops or trafic? Could be an electric fan not coming on early enough or other air-flow problem. Hope these ideas give you a place to start.
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Old 01-09-2003, 03:52 AM
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where is the sender ? i think they work better in the intake than the heads you will get some funny readings from the heads.
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Old 01-09-2003, 07:31 PM
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It has an overflow tank, new superstat when I installed engine, will do it at any speed entire time I'm driving, runs normal temp. warmer up grades and traffic with air on, everything seems normal except going to high side and then srifting back down. Have not noticed if it does it while cold or at stops but will check . Electric pusher fan is manual switch, sender in front of manifold, does not have teflon tape on it. When I get to a day off I'll replace the stat, (what's the odds of getting a good one the first time) drill a couple of 1/8 holes in it for air escape. I'll post follow up when I check this out. Thanks for all the suggestions
Larry
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Old 01-10-2003, 04:29 PM
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[quote]Originally posted by dodge36:
<strong> When I get to a day off I'll replace the stat, (what's the odds of getting a good one the first time) drill a couple of 1/8 holes in it for air escape. I'll post follow up when I check this out. Thanks for all the suggestions
Larry</strong><hr></blockquote>

You don't need the holes, most good T-stats
have a bleeder in them, or if you want, drill
a single 1/16th"er, air isn't that thick...
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Old 01-10-2003, 06:20 PM
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You don't need the holes, most good T-stats
have a bleeder in them,

If I knew it was getting through the bleeder I wouldn't need any holes. Motor is new crate 350HO but radiator isn't new, how much would it take to plug up a bleeder.
Thank for your help
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Old 01-11-2003, 08:23 AM
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One question, You didn't wrap the threads with a teflon tape did you? That's a no no. You won't get a good reading. you need a good ground and the tape does not make it have a good ground.

Just one of many things to look for
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Old 01-11-2003, 03:11 PM
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No teflon tape awsum. Same sender was in old motor with no problem. I know that doesn't mean it's OK now. It's possible it is going bad now, I'm not sure if they go out all at once or will fluctuate first. Should be able to check it out Mon. Thanks for suggestion awsum.

[ January 11, 2003: Message edited by: dodge36 ]</p>
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Old 01-12-2003, 09:51 PM
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You might want to get a mechanical guage to calibrate your elctrical guage to make sure things are what you think. r
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Old 01-14-2003, 03:45 PM
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Awsum,One other little thing does your wire going back to the gauge run in a loom with others?If so it might be picking up interference from them.Try seperating from others just to test .
Good luck
Ron
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Old 01-14-2003, 11:52 PM
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Sounds to me like you have a bad t-stat. Chances of getting a new t-stat that is bad is a pretty good chance. When I ran the parts store we would get several back that were bad from the box.
Also make sure that you 'burp' the system first, it also sounds like there is an air bubble traveling around in the system. When the motor is cold, take the radiator cap off, start the car and let it run for about 5 - 10 mins, watch the coolant level to make sure t-stat is opening and closing...if everything checks out, put the cap back on and take it for a test run. If it still does it, trace down the wiring.
Is it an electrical or mechanic gauge? It may also be possible that the sender is bad(on an electrical)
Later,
WEIMER
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