1972 Dodge D200 temperature sensor

[dsailer]

I purchased this truck recently and noticed the temperature was running nearly 230 and I tracked it down to the aftermarket Bosch gauge reading ~30 degrees high. I'd like to try to fix the stock gauge but running into an issue with the sensor. The intake is 1/4" NPT but it seems almost all sensors are either 1/8" or 3/8" and websites are indicating 1/8" is correct for the vehicle. The intake appears stock but I'm not 100% sure on that. Number on the intake is 3614038 (a bit hard to see that first number under the carb, but I think that's it). There isn't a date stamp, although there's a tag that doesn't appear to have anything on it. The ads for sensors aren't very good at specs, sometimes not even having the thread size, let alone any ohm range reading. I can't find the ohm range required anyway (I could test this, but need to get some equipment to do it). If I try to adapt 1/8" to 1/4" it seems I have to worry about the bulb length.

 

Maybe I'm over-thinking this, but this seems like a dead-end. Any help is appreciated. Thanks!

[3macboys]

That intake is a Mopar intake and the part number puts it in the right date range.  There will be a casting date on the top of the intake.  Best advice is to get a parts catalog for the truck if you don't already have one.  Not an expert by any means but there is always the possibility that someone retapped the intake for the Bosch sensor.  

[joe_padavano]

2 hours ago, dsailer said:

Maybe I'm over-thinking this, but this seems like a dead-end. Any help is appreciated. Thanks!

 

You're overthinking this. Bushings to adapt 1/8 NPT to 1/4 NPT for temp senders are common and won't make a measurable difference in the reading. The bigger question is, will the factory gauge be more accurate than the aftermarket one?

[dsailer]

12 minutes ago, joe_padavano said:

 

You're overthinking this. Bushings to adapt 1/8 NPT to 1/4 NPT for temp senders are common and won't make a measurable difference in the reading. The bigger question is, will the factory gauge be more accurate than the aftermarket one?

Ok, that sounds good. The truck is so stock, the hole in the dash with an aftermarket gauge seems a shame. So I suppose my options are to start buying sensors until I find one that reads acceptably. Or get technical and try to get ohm readings on my gauge and aftermarket sensors first - this seems like it will be a hassle. At least the stock gauge just had "C" and "H" so maybe i won't be so bothered by it being off by 30 degrees like the old one

[joe_padavano]

I'm curious as to how you verified that the aftermarket gauge was off. Did you use an IR thermometer or something?

[dsailer]

4 hours ago, joe_padavano said:

I'm curious as to how you verified that the aftermarket gauge was off. Did you use an IR thermometer or something?

Yea, I pulled the whole thing, boiled some water and checked with an IR thermometer. It was about 30 over at boiling. I was already pulling the dash apart to recover pads so figured I just dig into everything I wanted improved.

[JACK M]

8 hours ago, dsailer said:

3614038

None of my books show this exact intake casting number but as 3mac says it is right in the range.

Twer it me I would go with the bushing and stock sender.

[Jubilee]

Electric temperature gauges that run high are easy to calibrate.

Just add resistors to the wire until you get it corrected.

I usually add 5-10 ohms at a time to start.

Just bare the wire and twist the resistors on to the bare wire

Here’s a GM chart

[dsailer]

5 hours ago, Jubilee said:

Electric temperature gauges that run high are easy to calibrate.

Just add resistors to the wire until you get it corrected.

I usually add 5-10 ohms at a time to start.

Just bare the wire and twist the resistors on to the bare wire

Here’s a GM chart

That's good to know! But since that high reading gauge was aftermarket, cheap, and stuck in a hole drilled out of the panel, I'm looking to go a different route. After failing to find an NOS stock gauge, I'm looking at replacing the four small gauges with Auto Meter. I'm planning to try to re-use the bezel and it will be a little challenging to put 2 1/16 gauges in but that's part of the fun!

 

Thanks for all the well informed replies. I'll let you know how it turns out.

[dsailer]

I'm pretty happy with how the new gauges are looking. Was a PITA do get these 2 1/16" gauges in. I'm now trying to figure out the wiring and could use a diagram of the pin connections. I've traced all the wires around but one of them is looking like it should be power but is actually ground? I believe it's connection "A", the pin where the tab on the connection points.  I have the generic truck wiring diagram but it doesn't have this detail. I can find a diagram for A bodies, and it shows "A" as 12v. For me, "A" has continuity to ground. Also, the power for the light on the aftermarket gauge was wired to "A" but the light wasn't working. If anyone knows if the service manual has this diagram, I'll buy one of those (probably will anyway).