Aftermarket water temp gauge reads low due to wire length

[zoro4]

I'm working on a rear engine RV and installed a new water temp gauge and I noticed it's reading low by atleast 10*F. Called the gauge supplier and they assure me it's due to the long wire length but they really weren't sure how to deal with it.

My question is how do I correct the issue? Is there a resistor or something I can wire inline? There is a mechanical gauge on the engine so I know how hot it actually is running.

[zoro4]

eastfizz wrote:
I do not know what your altitude is, or how you are testing the gauge, however when I was testing a trans fluid temperature gauge with boiling water, it was reading about 200 degrees F when the water boiled. I thought the gauge might be bad or the wire was not large enough for the run to the trans from the gauge. After some checking, I determined the gauge was correct as water boils at about 200 degrees F at my altitude, 7100 ft. Hope this is helpful.

Best regards,

Lowell

7100 eh? I've got 2900 on ya:p Dunno if altitude is the issue or not but it might very well be.

[eastfizz]

I do not know what your altitude is, or how you are testing the gauge, however when I was testing a trans fluid temperature gauge with boiling water, it was reading about 200 degrees F when the water boiled. I thought the gauge might be bad or the wire was not large enough for the run to the trans from the gauge. After some checking, I determined the gauge was correct as water boils at about 200 degrees F at my altitude, 7100 ft. Hope this is helpful.

Best regards,

Lowell

[zoro4]

The sensor is the threaded sensor.

On the intake manifold for my engine(440 Mopar) there are half a dozen ports it could screw into for the various CTO systems that engine used in various car/truck/non-MH configurations.

[Daveinet]

What type of sensor are you using? I see on their webpage, a threaded sensor, which would typically go in the head or intake, and I also see one that is made to go on one of the rubber hoses. You state that the 2 sensors are as close to each other as possible. Does this mean you have 2 sensors mounted on a hose?

[jauguston]

You may be able to correct it but the trouble is quite likely not the extension wire. The engineer at Isspro told me for my pyrometer adding 40' of small 22-26ga wire would make such a slight difference in the reading it would be hard to measure.

Jim

[zoro4]

The new gauge is a digital GlowShift
http://www.glowshiftdirect.com/productimages/2010-blue-digital-gauges/thumbs/13_GS_BD_Water_Temp_Thumb.jpg

There is a mechanical gauge on the engine and the new probe is as close to the old one as I could get it.

It's funny because with the engine off and cold the new gauge is only 1*F off from the old one. The engine isn't close to overheating but I'm just curious as to whether or not this issue can be corrected or not.

[Gjac]

How did you determine that the gauge reading was 10 degrees off? When I replaced my temp prob it seemed to run hotter than the OEM prob. It bothered me for a while because the fan clutch seemed to come on much later. I decided to shoot the prob itself and the surrounding area with an IR gun. The readings were 15 degrees lower than what my dash gauge was reading. Also shot the thermostat housing it was also 15 degrees lower than the gauge reading.

[sflabrkr]

I'm confused, how do you know it's 10 degrees off
and why would you care. If your that close to overtemping you have another problem

[Daveinet]

I would suggest that induced voltages would be more likely to cause the display to be erratic, rather than just off by 10 degrees.

I am curious what type and brand of electronic gauge you are using. I just put an electronic gauge on mine and it reads about 10 degrees high. Really don't know if it is the fault of the gauge or the location on the engine compared to the one on my ECM, or maybe both.

[dangerbird]

If you are using a thermocouple, shouldn't you be using thermocouple wire? Length should not be an issue due to the low current/voltage involved. Induced voltages could be an issue with longer runs.

Carl

[garry1p]

I suspect the mechanical gage is at a different pick-up location than your add on gage. I doubt the larger wire will make more than at most a few deg change.

The temperature probe is really a variable resistor so adding a fixed resister in parallel while sounding good and may get you the correct reading at one temperature all other readings will be off based on the fixed resister.

If you know the new meter is off then put a mark on your new gage (red dot from finger nail polish) where the normal operating temp is based on the mechanical gage pretty easy to tell if it reads above the red dot you are running hotter than normal.

[More_To_See]

You are dealing with voltage & current that is practically zero. In the micro area. The wire gauge is practically meaningless. I'd looking at using shielded wires. And maybe lay out your sensor & gauge on the ground and run some tests with a kitchen thermometer in a pot of hot water. Your connections & noise are more likely problems - - if you even have one. 10 degrees between two water gauges on an engine may be completely normal.

[Daveinet]

Time for a reality check. The resistance at normal operating temp (200 degrees) is around 1K ohms. 18 gauge wire resistance per foot is around .5 ohms per 100 FEET ! A 10 degree difference is a about 100 ohms change. A poor connection could cause the problem, but not the wire gauge.

I should also ad that you could see some difference as a result of where the 2 sensors are mounted. Otherwise, I would suggest the sensor is probably off.

[wolfe10]

I would buy a spool of quality 14 gauge wire and just run it "fastest way", either outside the coach, or down the center of the coach. Attach it at both ends and see if it improves the accuracy of the gauge.

If so, take the time to run the new wire.