I’m ticked off at the moment because I ordered DAC5525 for my 3.6 Cabriolet and just opened the box to find the coupe fuel sending unit, DAC5500. The guy at Welsh Enterprises seemed convinced that there was no difference, but I know there is at least one post on the forum stating that there ARE differences (in calibration) across the three sending unit types:
Does anyone know what the exact difference is? The DAC5500 unit looks very similar to what I pulled out of my car, with the exception of having the updated black pedal-shaped float.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
2
Do you have both in your hand? Is the total range of motion about the same? I’m thinking the convertible and Cabriolet tanks might have lower tops to the tanks so the float does go up as high. Do you have a VOM? Can you check the resistance on each one and see if they are comparable?
If you simply installed that sender, I highly suspect the worst possible result would be that the gauge would read a bit different, like perhaps it’d continue to read slap full until you had used up 1/4 tank or something.
Hmmm. IIRC, those are the same usual suspect that insisted my 4.0 used a 3.6 air filter, despite their listing showing the correct filter for Superblue. They only recanted after I sent them a link to the Classic Jag website so they could see for themselves the proper fitment. They told me I could just keep the incorrect one and they would send me the right one (which they did). Sorry I tossed it, XK, or I could have forwarded it on to you for your Jag, if the shipping was covered.
I sometimes wonder if these “family businesses” don’t keep it within the family anymore and are hiring people who don’t know beans about out cats.
btw, regarding the fuel senders, I don’t know why there is so much variation in them by way of Jag. I have found out that the one for the '92 coupes, like Superblack’s (the only post-face lift 5.3 MY) are supposedly “unique” and almost unobtaineum.
Atty, That sucks that you got an incorrect part from them, too. I’m extra ticked off because they also have the DAC5500 part listed on their site…for half the price of DAC5525. So not only did they send me the wrong part, they charged me double for it…and the guy I talked to today before I realized the price discrepancy was extraordinarily condescending. He basically told me they were the exact same part, that Jaguar just makes up extra part numbers for no reason, and that they install that part on cabriolets all the time with no issue (maybe this is true, but if you can’t tell me why Jaguar had different part numbers I’m not going to believe anything you say). He also told me to “take it to my mechanic and they’d handle it.” Excuse me, I am the mechanic, which is why I am calling with questions!
Even if Kirbert is right and the only difference is that the gauge might take a little longer to go down with the coupe sending unit, I’m still pissed off because a) I still have my original sending unit and it’s fine other than the float, so I wouldn’t have ordered the replacement if I hadn’t thought I’d gotten lucky and spotted unobtanium, b) they charged me double for it, and c) their sales person today was pretty rude.
(Edited to add: I spoke to the original sales person I worked with and he refunded me for the difference in the cost between the two parts with no fuss).
Following up: got a hold of a VOM to test and compare the two sending units. The arms do move the same amount, and the shape/construction for DAC5500 and DAC5525 seems outwardly identical.
VOM test results:
DAC5500
at empty: 198 ohms
at full: 42 ohms
DAC5525
at empty: 198 ohms
at full: 45 ohms
I’ve read elsewhere that normal range for these is 20-220 ohms, so I guess they are within the normal range, if in a slightly narrower band than that. It’s maybe worth noting that the values seemed to jump around quite a bit and didn’t hold very steady during the test.
In the end, I’m going to replace my float on my original sending unit with a brass Ford unit as recommended in the book (part number C0AZ-9202-B). My float has fuel in it. I’ll keep the DAC5500 around as a spare in case it becomes unobtanium like the DAC5525.
They only recanted after I sent them a link to the Classic Jag website so they could see for themselves the proper fitment. 
They told me I could just keep the incorrect one and they would send me the right one (which they did). Sorry I tossed it, XK, or I could have forwarded it on to you for your Jag, if the shipping was covered. 
I have found out that the one for the '92 coupes, like Superblack’s (the only post-face lift 5.3 MY) are supposedly “unique” and almost unobtaineum.