Gauge problems...


Old 07-23-03, 06:16 AM
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Join Date: Mar 2002
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Gauge problems...

I have a 1988 Chris Craft that I just bought a month ago. It's a Merc I/O, 4.3L, Alpha1 outdrive. I've noticed the the fuel gauge, trim gauge and speedo do not work. Occasionally the speedo will move, but it seems to hover around 20 mph, the fuel gauge always hovers around 1/2-3/4 of a tank, and the trim gauge is pegged at full trim. I was hoping there were some common troubleshooting steps for these, that I could use this weekend when I tackle the dashboard. Any hints? The rest of the gauges work fine. Any help would be appreciated.

Oh, and one more ?? Where as the boat is trailered, and in covered storage when not in the water, Do I really need to put a marine radio in it, or will a regular car stereo be sufficient?
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Old 07-23-03, 11:47 AM
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The speedo works through air pressure from the lower unit. At the leading edge of the drive, you'll see a small hole. As the boat moves through the water it forces air/water into the hole which is connected to a tube running up to the speedometer. The tube often gets glogged with sand or scale and gives bad readings. (Not that they're that accurate to begin with.)

Remove the hose from the back of the speedo and blow it out with air from that end, making sure there isn't anything in the hole on the front of the drive. A toothpick can be used to check/clean out the hole.

Have an assistant make sure the air is blowing out of the hole.

Inaccurate gas guages are almost always the sending unit. There should be an access cover to get to the top of the tank where the sending unit is. Remove the cover and unscrew the float/sending unit assembly. (Remember safety, you're dealing with gas and gas fumes at this point)

Move the float up and down on the travel arm and see if the guage moves accordingly. You can adjust it by bending the float arm or other component to read full, when the float is at the top of it's travel, and empty at the bottom. Remember that the "Empty" reading is much more important that the "Full" reading.

If the guage doesn't move, you may have a bad sending unit OR guage. Replace whichever is cheaper, first.

Trim guage is best left to a Mercury mechanic to troubleshoot. There may be wear in the contacts of the trim indicator on the drive. You may be able to check wire connections for corrosion, and clean them if neccessary. Sometimes that clears up the problem. (Last sentance applies to any faulty reading guage.)

The car stereo is OK, as long as it is protected from getting wet from spray, splashing, or dripping bodies.
Old 07-23-03, 06:04 PM
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They also sell waterproof aftermarket covers for the stereos, not sure how waterproof they are but it may help in keeping it dry.
Old 07-23-03, 10:06 PM
BoatMech's Avatar
Join Date: Dec 1999
Location: Los angeles
Posts: 592
The trim/limit senders are not servicable. many have tried.
The best bet is to replace the pair.
Sometimes the wires inside have rotted or become corroded and as boatcop suggested, check all the wiring
Old 07-24-03, 07:42 AM
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Join Date: Mar 2002
Posts: 30
Thank you all very much, I'll give it a try this weekend.

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