Water temp gauge question

[thebeebe5]

Sadly the "heat" gauge in my cluster no longer works.  Some conscientious PO actually cut the lead off the back of the gauge and I don't know if that can be repaired....  BUT someone else added a John Deer gauge a long time ago so...  Wait.  That doesn't work either. :-(

I need a new gauge.  I'll undermount it where the JD is.  What size is the NPT fitting on the head?  Also, how deep of a probe can I use?  Would like to avoid draining coolant at the moment just to determine the depth dimention so if anyone can help that'd be great!

[Roadkingcoupe]

If you search this site there is a handy article how to "graft" your old gauge to a new capillary tube.

 

(edit: Tod Fitch has added the link to the article two posts down).

 

Temperature Gauge Sender Unit Replacement
By Jim Leman

Replacing the temperature gauge unit on your P-15 is a service best undertaken when you are in a patient mood. As with most jobs requiring work under the dash, this task will test your patience. You will want to replace a broken or defective temperature gauge sending unit because without it you will lack information of a critical aspect of engine operation, water temperature. Temperature gauge sending units fail for various reasons, often from kinks or breaks in the capillary tube. This tube is inside a coiled outer protective wire shield running from the sender bulb to the gauge unit itself.
 
Replacement units can be purchased from any well-known Mopar parts suppliers, both those who market through catalogs, the major old car publications, the Mopar car club periodicals and occasionally they can be found both used and NOS as swap meets. Expect to pay from $100 to more than $200. Inspect the unit carefully, especially the sender capillary tube for kinks and breaks. Test the unit before you install it in your car. Fill a glass or cup with water heated to a predetermined temperature, say 180 degrees, and insert the bulb unit into the liquid. The gauge needle should begin to move slowly and settle on or very close to the gauge face temperature marking that corresponds with the known temperature of the water. If the gauge is working right, lets head to the garage. Get to know the project. Open the car hood and place your fender blanket and tools on the driver’s side fender or bring your tool cart to your side. Hang your shop light so it illuminates your work area brightly. Disconnect the battery ground. Drain the coolant by opening both the radiator and block petcocks. If you don’t coolant will run out onto your clean shop floor when you remove the old temperature bulb from gland nut in the side of head.
 

You will find this gland nut in the left (drivers side) of the head nearest the firewall. The bulb sits inside a tapered, threaded part known as the radimeter gland nut. The nut is a threaded into the head. To remove the old nut, use a little penetrating oil to ease your effort. Loosen it and back away the retainer and then slide the bulb carefully free of the nut. Clean all threads. To reinstall, reverse this procedure. When the retainer is tightened against the gland nut, it will secure the bulb and prevent coolant from leaks. Use thread sealer for insurance.


Getting set up: Here’s a helpful hint on positioning yourself for removing the gauge unit from the dash. Position yourself in the passenger compartment like slat, head and torso under the dash with legs and feet over the back of the front seat. Before you get into position though, first pull the throttle knob out full. This will depress the accelerator pedal. Place a rag or old tee shirt over the pedal to provide a cushion for the back of your head when you’re in position. Make sure you get all your tools in position first too. Hang a shop light (I prefer the cooler florescent type) so it illuminates the underside of the dash. Having two lights carefully positioned will help to eliminate or reduce the harsh shadows you’ll get under there with just one light in action. Position the tools you’ll need on the floorboard or on the front seat where you will be able to reach them when in position. The tools you’ll need include a flashlight, a long shaft slotted screwdriver, preferably a magnetized one. Leave the beer in the house.

Clearing a path: You might want to remove some underdash clutter before you start. First, remove the headlight switch. The knob removes by inserting a narrow slotted screwdriver blade into the slot on the underside. This frees the knob from the shaft so you can remove the panel nut and slide the switch free from the other side. Bag any hardware removed and label it. You may want to use tape to tape up the switch or let it dangle free. I also found it almost impossible to access the gauge without removing the speedometer unit first. The speedometer is held to the backside of the dash by a few screws across the top and bottom of its housing. When these screws are removed and the speedometer cable removed from the unit, you should be able to jostle the unit free and clear. Place it were it won get damaged. Now, with your long-shafted magnetic slotted screwdriver, find the retaining screws in the back of the gauge and remove them. Keep the screws in a safe place. Unfortunately, the gauge doesn’t pop free, but it too requires plenty of jiggles and a little cussing to convince it to come free of the dash. Try moving the unit up slightly and to the left (as you view it under the dash) to clear the edges of the housing frame. If it doesn’t come free after a few minutes, sit up in the drivers seat, reach up with your arm under the dash and take the unit in hand. Move it to understand how it comes free of the dash glass and how you must move it to free it from the housing. Remove the unit. You’re almost done! To install the new unit, first remove the clip from the firewall grommet through which the sender wire will travel. From inside the car, with the gauge, wire and sender bulb carefully resting on your floorboard or accelerator pedal cushion, carefully push the new sender bulb through the grommet. (A lubricant like ArmorAll here eases the penetration). Now, from engine side, carefully pull the bulb clear of the grommet and with sufficient slack that it touches the gland nut head. Go back inside the car and get into position again. Carefully pull the wire and gauge unit up and through the confusion of wires and stuff behind the dash. Just as you removed the old unit from the dash, install the new one. Use care when feeding the gauge face back into its housing so you don’t damage the delicate needle. You may need to make a paper gasket for the unit first and install it on the gauge face where it mates to the housing. When the unit fits into its housing, insert and tighten the retaining screws you had carefully set aside. Reinstall the speedometer, headlight switch and any other components or wires you may have removed. With the gauge in the dash and capillary tube through the firewall, insert the sender bulb into the gland nut in the head carefully securely. Use some sealer on the retainer nut and tighten against the gland nut. A firm snug and then a nudge is sufficient.

Finishing up: Refill the radiator with coolant and restart the engine. Check often for coolant leaks at the gland nut and both the radiator and block petcocks. Keep an eye on the gauge. I t should begin to move as the coolant warms, and it should stop when the coolant reaches the temperature allowed by your engines thermostat. Replacing the temperature gauge on your P-15 takes a little time, but you can do it yourself.
 

Edited May 31, 2015 by Roadkingcoupe

[Don Coatney]

There is lots of room inside the head for a replacement probe. And most aftermarket gauges come with an assortment of gland nuts that will fit the tapered pipe threads inside the head. Make sure you use pipe dope on the threads.

 

 

 

[TodFitch]

You may also be able to repair your original dash unit. See http://www.ply33.com/Repair/tempgauge

[pflaming]

I mounted an aftermarket gauge on the bottom edge of my dash and had Kevin B3B repair mine. Came back like new, just like all his gauges and speedometers. Love my gauges.

The coil and tube therein, will short out on any hot post, etc., and will likely be ruined. So disconnect a battery cable and avoid that possibility. Don C clued me in on that, TKS Don.

Edited May 31, 2015 by pflaming

[thebeebe5]

Thanks fellows. I'll probably go the easy route and get an aftermkt gauge for the time being. There's a Stewart Warner one I like and the lead isn't ridiculously long.... Glad to know I have generous room for different probes.

Will look into repairing the original at some point in the future.

And thanks also for fielding my many questions.

There will be more to come!

[belvedere666]

it's easy enough to repair your old one, using the tutorial above, if you're good with a soldering iron. i found out that i wasn't as good as i thought i was, which was "just good enough" to repair the things i've had to repair up to now.

a donor gauge that you can get for like $20 with the capsule at your local auto parts. comes with a gland nut. a piece of brass tubing that was $1.00 at the hardware store. solder, flux and a soldering iron. ice and salt.

it helps if you have a dremmel or something handy to widen the copper tubing a little for the best fit.

i got it all put together and dropped it in hot water and the liquid gas (from freezing it) squirted out all over the place from the holes in the solder joint. luckily i cam across a working one from a fellow board member.

 i would have had to try my luck at sacrificing another donor gauge.

but again, if you're good with solder.... all the prep up to the point of solder is easy.