Factory gauge cluster

[87GrandMarq]

For you guys that have 90-91 boxes, how accurate are the gauge clusters specifically the coolant temp gauge? A couple months ago I noticed that the gauge would fluctuate a lot. It does this odd thing where it’ll slowly climb to around the A or L or normal, then quickly fall back to center. At first I thought maybe it was the water pump going out but it doesn’t seem to always follow the rpm’s. It’ll do it pretty regularly while idling then sometimes it’ll do it while accelerating, but not always. Anything I should check? I have a temp sensor on the way to verify how hot it’s actually running.

[Arquemann]

Could be a sticky thermostat if it hasn't been like that always.

[DerekTheGreat]

^^^ Might be worth checking the coolant level too.

[VicCrownVic]

Make sure your coolant is at the correct level. I had air in the cooling system of my '98 when the cooling fan connector shit the bed and boiled out most of my coolant. After rigging the connector to stay connected, I couldn't get very far without the dash beeping at me that the temp was too high. Once I filled the cooling system it stayed normal the rest of the 40 miles home.

As for accuracy, I'd say it's best to note what each car typically runs at. The gauge in The Scab always read lower than the gauge in The Ice Car, but I doubt they ran at that much difference in temp. (I ran a 2001 P71 cluster in The Ice Car the last 5 years that car was on the road. Not a direct swap by any means, and physically not the best fitment.)

Edit: forgot to hit the "Post Reply" button and Derek snuck in and said the same thing.

[gadget73]

I've seen gauges dance like this with sticky thermostats, especially with overly large radiators or when its really cold out.

but yeah they aren't usually super accurate, change the sensor and it reads somewhere else, different cluster can also read slightly different. Its usually repeatable per-car though, so if it normally hangs in one spot but then suddenly moves, its usually telling something changed.

[Tiggie]

The mechanical gauge in my 88 reads quite nicely, stre. The stock gauge in my 90 does fluctuate quite a bit. I don't know if it's overly sensitive, or another issue. Never goes above half the gauge.
I would replace the thermostat if I were you. I prefer a premium thermostat.

[87GrandMarq]

I’ve had issues with the speedometer, odometer and trip ever since I pulled the cluster to install new odometer gears. The speedometer works fine initially but as time passes it starts to get stuck or jumps from one speed to another. The odometer works intermittently and the trip doesn’t work at all. My first thought was the cluster causing the coolant temp gauge to act erratic but I checked the coolant and it was pretty low. There must still be an air bubble somewhere as after I filled it up it wouldn’t warm up. I’ll screw with it after my long work weekend. I appreciate it. Any ideas about the other gauges? I’d like to diagnose it before I pull the cluster again. It’s such a pain to pull the cluster in the 90+ boxes.

[DerekTheGreat]

Lube the speedometer cable up as well as the speedometer mechanicals themselves. I like to use ATF. Put some in a small cup and use a pipette to drip it in, won't make a mess. I don't know how the odometer works in these, 90+ might be electronic. In either case, I'm betting there's a drive gear and a driven gear. It's plausible the gear(s) have a crack and spread apart at times, causing the intermittent issue. Need to open it up to figure out what's going on.

[87GrandMarq]

It’s all electronic, no speedo cable. I kind of wish it did for simplicity. The gears are brand new. I guess I’ll have to pull the cluster and check them out. Who knows, they could’ve grenaded themselves.

[sly]

Sometimes there's a little casting flash on the plastic gears that needs trimmed off depending on the supplier. A little dab of silicon grease or a shot of silicone lube will help with plastic gear interface as well.

[VicCrownVic]

I don't remember if I'm imagining this, but I seem to recall putting one of these clusters back together and it was possible to get the individual gauges not quite seated all the way. Since there is mention of the issue happening after installing new odo gears. Could be worth making sure the gauges are fully seated.

The VSS on '90+ is the same as the earlier boxes with the only difference being that they have a cap to cap off the cable connection used by the earlier boxes since the speedo is electronic. Since it's not just the speedo giving you issues, it's not likely the VSS or its driven gear. It be a heck of a coincidence if it was the speedo problem, but highly unlikely.

Honestly, I much prefer working with the '90+ clusters, LOL.

[87GrandMarq]

I know I oiled the gears but I’ll pull the cluster and check the gears again maybe on Monday.

I didn’t know that about the 90+ vss, good to know. I’m thinking it’s just the harness or the printed circuit board bent or something.

[sly]

Yeah... the traces like to peel off the plastic at the connector. Making sure they are flat and in position and be very careful to plug in the connector without backing out again helps keep that all working.

[87GrandMarq]

I pulled the cluster, cleaned up some contacts and made sure the gears rotated freely and actually engaged, which they did. I bolted everything back up and made sure the two connectors were fully sat and it’s still the same but now the speedometer acts up from the get go unlike before. It does work when you tap on it it’ll go to the correct speed but if you speed up or slow down it won’t move or if you stop it’ll sweep to 0 in incriments. And the odometer and trip are totally inoperative now. It’s crazy because all of this started after I pulled the cluster the first time.

[DerekTheGreat]

That's goofy. I'd suspect the speedometer stepper motor is toast. As for the odometer, I've got NFC. The only experience I have is with early GMT400's- They're also fully electronic, but there's a little motor which has a plastic gear press fit over the output shaft of the motor, which drives a plastic gear on the trip odometer, which is in turn connected to the odometer. My drive or driven gear must have a crack in it, as I have to keep resetting the trip odometer in as little as 9.9 miles when one of those gears splits apart. Been saying I'll fix it for about a year now.