Aftermarket water temp gauge reads low due to wire length

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.

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.

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.

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.

Not the same type gauge but when I installed a Isspro pyrometer with 40' of extension wire I called Isspro to see what that long extension would do to the reading. They said it would make it read higher by .1%. The wire was exterior phone cable about 24 ga.

Jim

Sorry Zoro, I was thinking of another gauge....old age I guess...but bump up your wire size to 14ga and your problem will go away....Dennis

How do you know which gauge is correct? Just because it's a mechanical gauge does not mean it's absolutely correct. A differential of 10F between gauges would probably fall within the reasonable range of tolerances.

Most gauges are not extremely precise. They are intended to give the operator a good idea of how well the engine is operating relative to the values they are reporting, but usually they do not provide extremely fine readings. A 10F error would not be considered out of line, generally speaking. That's why when one sees a gauge getting close to red line it's usually time to stop and find the problem.

Having said that, for really long runs between the electric sender and gauge, a larger diameter wire would be a very good idea. The exception would be if the gauge is intended for rear-engine RVs, in which case it should come with an appropriately sized wire (but I wouldn't depend on it sometimes).

Run the best quality 16 or 14 gauge wire you can buy. Judge the quality by the number of strands in the wire, more strands the better, also more flexible.

Executive wrote:
If they're saying it's because of the wire length, what they're really saying is the wire GAUGE is too SMALL. If you're using 18ga, bump it up to 14ga. If 16GA bump it to 12ga. You could also use a relay if you've already wired it.....Dennis

Dennis-
Running 18ga wiring.

How would a relay help me out? The gauge measures resistance across a thermocouple and the long run of wire is between the thermocouple and gauge.

If they're saying it's because of the wire length, what they're really saying is the wire GAUGE is too SMALL. If you're using 18ga, bump it up to 14ga. If 16GA bump it to 12ga. You could also use a relay if you've already wired it.....Dennis