Need coolant temperature gauge

[Sean]

Folks,

As always, when I get stuck with problems like this, I turn to you all here on the board.

My temperature gauge is kaput.  Grounding the signal input, which should deflect the pointer all the way to the right, does not move the needle at all.  The gauge bezel is pressed onto the housing, so the gauge is "sealed" for all intents and purposes and I don't see any way I can repair it.  I need a replacement.

While temperature gauges are a dime a dozen (well, OK, a decent new one is $25), this gauge is a bit different than anything available off-the-shelf, and I'd like to replace as many of the features as I can.  I harbor no illusions that anyone here has an exact replacement or can point me to one, but here's the list of, umm, "weirdness":

• It's a 63mm (~2.25") European gauge, as opposed to the 2.065" of most US gauges.
• In addition to a lamp well for backlighting, there is an additional lamp well behind a little red window next to the 210º mark, for a warning lamp (the lamp is separately wired from the gauge).
• It's 24-volt.
• It has the Neoplan logotype across the dial face.

I am mentally resigning myself to having to "neck down" my 63mm opening to 2.065", add a separate warning lamp elsewhere on the dash, put a big honking voltage-dropping resistor in, and just get a VDO unit that at least looks similar.  However a replacement possessing any of the above features would be a step in the right direction.

The existing gauge is a VDO, part number 310.475, OEM for Neoplan and calibrated in ºF from 105º to 250º.

I have combed the web but come up empty, and I now have emails in to my various Neoplan parts sources.  If anyone here either has one lying around that might work, or can point me in the right direction, I would appreciate it.

For the curious, I also get coolant temperature on my VMS display from my DDEC, so it's not like I am driving blind right now; the analog gauge is really a backup.  Also the DDEC and analog gauges read from opposite sides of the engine so having both working gives me a little more insight into what's going on back there.

Thanks in advance.

-Sean
http://OurOdyssey.BlogSpot.com

[Zeroclearance]

Sean I can vouch for these folks.

I send all my VDO gauges to them..

http://www.paspeedo.com/

[Sean]

Funny you should mention them...

When I lived in that area, I used to take all my vehicles to them to get the speedos calibrated.  I had something of a lead foot in those days, and there was no way you could argue your way out of a ticket in court if you did not have an accurately calibrated speedometer with a calibration certificate within a year or less (the idea being that, all else being equal, the speedo in the police car is more accurate than yours, and the departments kept them calibrated for exactly that reason -- often at Palo Alto Speedometer).

Anyway, I know they repair VDO and I will be calling them tomorrow.  I also have an email in to Bob's Gauges, another VDO repair outfit.  I am bracing myself, however, for a bill well north of three figures.  I haven't really decided yet how much past Ben Franklin, if at all, I am willing to go just to have a matching gauge.

Thanks for the suggestion.

-Sean
http://OurOdyssey.BlogSpot.com

[Sean]

Update:

At the risk of finding myself over at "There, I fixed it" (http://thereifixedit.failblog.org/), I, umm, fixed it.

After searching high and low for a direct replacement and coming up empty -- even "normal" 105°-250° temperature gauges in 24-volt are a rarity -- and calling around for repair estimates which start at $85 and go up, depending on the problem, I decided I had nothing to lose by attempting my own repair.  I do still have feelers out to two fellow Spaceliner owners who removed their gauges, and if they come up with one that works I will take it, because this one is clearly on its last legs.

The hardest part of the whole repair was getting the case open.  When I first posted here I thought that was more or less impossible without destroying the gauge, because the crimp was so tight all the way around the housing that I could not even get a jeweler's screwdriver under it.  Ultimately I was able to worry it long enough with the tip of my pocket-knife blade to open a gap big enough for the aforementioned jeweler's screwdriver, and then I was able to work up to successively larger screwdriver blades until I got the crimp open all the way around.  I would say opening the case took a bit more than an hour.

The second-hardest part was removing the pointer needle without destroying the pivot or bobbin.  I was able to get a very fine needle nose onto the spindle to hold it in place and then pop the needle off with a miniature pry bar.  And "pop" is a good description; when it yielded it flew across the bus a good four feet or so.

Once I got the dial face off I found a broken trace on the PC board affixed to the bobbin holder.  It was the main power trace bringing the 24 volt source over to a 220Ω dropping resistor.  The trace burned through right where it passed behind the dial mount, which is grounded, making me think there was a brief arc there at some point.  No way to get a drop of solder on it with the mount in the way, and no room for a wire under there, so I had to run a wire around the outside of the bobbin holder.

After replacing the dial face and pointer I tested the movement with a potentiometer and all looked well, so I buttoned it up, staked the bezel down lightly in a few places, and put it back in the dash for testing.  I could only get the coolant up to 147° on high idle while parked here, but the pointer tracked pretty well to that value.  I'll know for sure when I start driving, as these sorts of meters are only accurate in their "sweet spot" (around 200° for this meter).  But that was good enough for me to completely stake the bezel back on all the way around.  That was nearly as tedious as removing it using only a screwdriver and working my way around the housing.

The dash is all back together now, and hopefully my repair job will last at least until I can get my hands on a proper replacement gauge.

-Sean
http://OurOdyssey.BlogSpot.com

[belfert]

For future reference, 12 volt gauges are often converted to 24 volt with a resistor.  My Datcon gauges except the voltmeter and tachometer all have resistors to use a 12 volt gauge with 24 volt.  Datcon makes a special resistor that mounts nicely on the back of the gauge.

[Sean]

For future reference, 12 volt gauges are often converted to 24 volt with a resistor.  My Datcon gauges except the voltmeter and tachometer all have resistors to use a 12 volt gauge with 24 volt.  Datcon makes a special resistor that mounts nicely on the back of the gauge.

True, but in order to use this method you need the value of the resistor from the gauge manufacturer.  I spent a good deal of time trying to find what that value should be for stock VDO gauges but, again, came up empty.

Having now opened my 24-volt gauge up, I could venture a guess that the value is 220Ωfor VDO gauges.  That's a big resistor -- dropping ~14 volts with a 220Ω resistor dissipates 0.89 watt; the one in the gauge was a big ceramic job that had clearly put out a bit of heat over the years.

If I had ended up with a 12-volt gauge, I think I would have used a LM7812 voltage regulator chip instead.  Less power and therefore less heat, and about the same size.  Plus no need to know what resistance value would be required.

-Sean
http://OurOdyssey.BlogSpot.com

[rv_safetyman]

Holy Cow you really go for the top dollar solution   $.70 for one and if you only buy 4800 at Digikey, they cost a whoppin' $.20!!

Neat solution.  We use them is a couple of things we make to allow up to 48 volts input and 5V operating system. 

Jim

[belfert]

Having now opened my 24-volt gauge up, I could venture a guess that the value is 220Ωfor VDO gauges.  That's a big resistor -- dropping ~14 volts with a 220Ω resistor dissipates 0.89 watt; the one in the gauge was a big ceramic job that had clearly put out a bit of heat over the years.

I recently replaced my gauges with completely sealed ones from Datcon.  Some of the original resistors were somewhat charred.  I purchased new resistors as they were cheap.