Technical Water temp gauge acting weird

So I hooked up my gauges and started it for the first time and the autometer water temp gauge just pegs at the max 250 after the motor was running for like 5 min .So I figure its prob the ground so I check today and unhook the wire from the sender and it doesnt move so that I figure eliminates the ground wire .Then I check it with the sender hooked up again and without the motor or anything being run all day it goes up to like 150 deg .I can figure out what would do this and i did use the sender that the gauge came with .I did use aluminum adapter that the sender is screwed into .Any ideas

 

Did you try using something to ground the sending unit or take the wire off and ground it to a good ground. Sometimes if there is teflon tape on the sending unit, it doesn't ground well. Otherwise I would contact Autometer.

 

I put the sending unit wire to the manifold bolt and it went straight to 250 fast .I didnt try grounding the sender separate tho

 

We need a little more information,what is the engine? new build? are you running a 50/50 mixture of water & antifreeze? is the radiator full? what type of fan? HRP

 

Double check your wire connector at the sender for possible high resistance, mine climbed up to 250 driving down the road, then I saw it jump a couple of times between 185 and 250, but mostly stayed at the top of the red.
When I pulled the connector off the sender the wire pulled out. Fixed that and all good

 

New gauge but the motor has like 500 miles ,yeas 50 50 mix and electric fan ,383 stroker .
Like I said when the car hasn't even ran the gauge goes up to 150 slowly tho with proper speed not like instant when I turn ignition on .I ran motor for like 5 min and it went to 250 and the radiator wasn't overflowing or anything

 

I had similar problems with a new build and the first thing the gauge mfg asked was if I had used a common ground on the gauges. I did and when I grounded each separately the problem went away and gauges worked correctly.

 

Make sure the sender matches the gauge and that the sender is designed for the voltage while running. We had one that read correctly til the alternator kicked in. Williamson's matched the gauge to the sender at prescribed voltage.

 

Where is the sender located? In the intake, or the side of the head? Could there be a pocket of steam there that is actually reading 250?

 

Hey, Bert; Would you be good enough to say what gauges you used? I'm having a similar problem as the OP, but not quite as severe. I'm using a low-buck gauge set, and the only one that seems to be acting up is the temp gauge.

Roger

 

Gauges work by reading the resistance of the sending unit. With the wire removed it should read one extreme and when grounded it should read the other extreme. If the gauge goes up when the wire to the sending unit is grounded and it still reads too high with the sending unit disconnected it almost has to be the gauge. You can test the sending unit by testing the resistance after putting it in cold water then check it after submerging it in hot water.

I've had a hard time finding decent gauges these days as many manufacturers have them made offshore and quality is poor.

 

I did some experimenting with this on an OT installation and found it is not true. I measured the resistance both with and without teflon tape in several of the connections and found they were exactly the same that could be measured with a digital multimeter.

If you look the gauge fittings are interference type and fit that cuts right through any tape at the threads making metal to metal contact.

 

Roger I used Dolphin gauges

 

I had my 6 volt gauges converted to 12 volt by a reputable company when I wired my car. Since day one the oil pressure gauge has been erratic. They sent me another sending unit but it did not help. I was concerned that I would toast my engine so I installed a mechanical gauge and found out I have great oil pressure. The gauge package was wired by the company with a common ground. I am going to run a separate ground to the gauge, as you did and hope it clears up the problem. My question to you or someone that has electronic experience is what difference will it make with a dedicated ground rather than one that is "daisy chained" across four gauges.

 

i did figure out my problem .My ground wire was damaged and when i replaced it worked fine

 

As I suspected. If I'm not mistaken, those are also a "budget" brand. Mine are the Omega gauges from Speedway. I too, have a common ground for my gauges, but I'm only running a pressure, temp, and voltage gauge. I would hardly think they should be influenced by a common ground.

If I'm not mistaken, these gauges work on the basis of a varying resistance through the sender to ground, as temp (or pressure) increases. It seems to me that if your gauge is reading high, then one could add a fixed-value resistor in the sender wire to bring up the resistance value to nearly correct. One would have to experiment some in order to get the right value in thier particular case.
In my case, the temp gauge is reading about 115 cold, key on, but not running. It also reads about 225 running temp, well warmed up. I hit it with an i/r temp gun, and the water neck was 185, the radiator top tank was about the same, with a 195 thermostat in the engine. I think I'm going to have to try a little trial and error to see if Ohm's law applies. I'll keep some records and post back.

Roger

 

National Pipe thread is tapered and should connect to ground. You run into a problem if someone gets carried away with the tape and doesn't tighten it enough.

 

Thanks for the update. Glad you got it working.

 

I'd like to get in this, but can't find an ohm sign on this blankety-blank keyboard!
...sounds like your gauge is 'looking for a ground'... (intermittent 'lazy-8' infinity?)

...Electronic resistance hampering feeble attempt at D/C humor...mixed with copious amounts of Clan MacGregor Scotch whiskey...