First off, When we talk of coolant
sending unit, there's two, located pretty close to each other, the one with only one wire going to it is only working the gauge in the cluster, the other coolant sensor with 2 or 3 wires going to it only "talks" to the pcm......I just want to make sure when you talk about changing the coolant sensor, that your talking about the one that has the one slip-on wire, the multi-wire one has a clip on connector........
On the gauge reading, if the thermostat was missing, it would take forever to get that gauge to read anywhere near normal, keep in mind the
oem stat is a 195 and if equipped with the 195 working proper, that gauge should be standing straight up and down(right in the middle of the normal range), assuming that your instrument cluster is working proper, your low reading may be coming from someone installing a 160 or 180 stat, now I can tell you that I use a 180 stat and when she's warmed up, mine shows just inside the "normal" range, so if yours is lower than that it may be a 160 in there........
On the vss, you said you had near 90k on the car, if that vss has never been swapped, I would swap it out, try to get a
motorcraft if you can and keep in mind that sensor is pretty snug in there, got to really wiggle and pull to get it out and try to put just a tad of grease around that "o-ring" going back in just in case you have to pull it back out in ten or so years, it will not fight you as much the next time...
On the
speedo reading, I'm not wild about messing with the needle, I'd find another way first, vss, cluster replacement etc. first.......Now you mention not only a problem with
speedo reading but with fuel reading also, I starting to suspect a possible faulty instrument cluster, I started having off reading on my some of my gauges years ago, I swapped out the cluster with one I found on e.bay that had 45k on it, now all gauges work proper, keep in mind these clusters are 30 years old, it would not be beyond me to think you may be dealing with a cluster issue........
On the fuel gauge reading, I'd say two things, either the
sending unit in the tank or once again the cluster itself, my thought is maybe rather that tackle all these different issues it may just be more easy to try a different cluster, and try to remember if you find a nice clean used cluster, find one that has that fuel gauge, anti-slouch, check gauges(many different names) still stuck in it, this card is about the size of a credit card and is shoved into the back of the cluster on the right side sitting in the drivers seat looking at cluster, now I hate to be long-winded, but "IF" you are dealing with several different issues AND your cluster is o.k., it's possible that the fuel gauge can be fixed by simply pulling cluster out and pulling that fuel card out cleaning it up and shoving it back in.........
