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MDC Controller Help?

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Can anyone help me with my specific problem with my Medallion MDC-1600 gauge controller?

I had water dripping slowly on my leg when I would go faster than idle speed. (at idle it would not leak) When I look up under the dash, it was easy to see that the leak was coming from the bottom of the MDC unit where the speedo tubes enter the unit.

I tryed to fix it by tightening the white plastic screw that attaches the tubes to the unit, but only made the leak worse. I contacted an expert at the company that made the unit and he was of no help at all. (he even said that there should not be any water in the line and instead air????)

So, I now have the unit off of my boat and can see theat the little "box" where the white connctors go into has a couple of hairline cracks that are allowing the leak.

My questions for anyone who knows about these units is:

1. Should there not be water running through those tubes to register the MPH of the boat? (if it should be air, then I have an even bigger problem than the small cracks)

2. How would I seal the cracks so that they would not allow water/air to escape? (the MPH reading seems to be good, but I would think a leak would make it less accurate)

3. If I cannot fix it, how can I buy a new unit, and is there a way to buy one used to save $$$?

Thanks to anyone that can help me get this fixed before the spring.


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You're gonna need a new control unit at about $300.

The system of lines that go from the pitots to the control unit has to be air tight. If it is, no water will work it's way up to the control unit. The control unit has diagphrams in it that measures the air pressure (I guess) the faster you go, the more pressure on the diagphram, the more the speedo reads.

If there's any air leakage in the system at all, water will go all the way up the line. Once water enters the control unit, it's just a matter of time before it fails. The first sign of failure is that it will draw too much parasitic current off of the battery when the boat is off. You'll leave your boat sitting for a week or two and the battery won't be able to crank the motor.

Once you replace the unit, do as good a job as possible to make sure those two rubber lines are sealed onto the white nipples.

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Thanks Pete!

Sounds like you've had some experience with this type of problem in the past. Help.gif

Any suggestions where I could buy the new one? Do I need to go to a Bu Dealer or should I go to Medallion manufacturer?

(the name of the company escapes me, but I found it about a month ago when I was in e-mail contact with the Rep)

Thanks for the help and info on how the system works....


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My advice would be if you're going to have to replace the MDC anyway, why not live with it until the gauges go dead (as long as the gauges are still accurate). If you can stand the water dripping on your feet, why not wait and not spend the $300 until you have to. Be careful if you get freezing temps overnight. If the water that has gotten in the MDC freezes, the MDC is toast.

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I have a 98 sunsetter that has had 4 MDC's put on it. Every spring my gauges wouldn't work. I finally figured out that during the summer months of use, water was getting into it and it would freeze in the winter. Basically cracking the MDC over the winter. I now remove it when I get the boat ready for winter, only two screws anyhow. Put it in the house and so far I haven't had a problem in several years. They say that water isn't supposed to get to it, but it does and doesn't take very much to cause a problem when it freezes.

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Thanks. I agree that I will attempt to use this unit until it goes bad so that I can hang onto my $300 as long as possible.

The drip is now a constant "squirt" that hits my leg and then puddles on the floor and ends up all the way in the back of the boat. So, I can't live with it as is.

Althought JB Weld could block the tube, I do think I will try it with caution to see if I can stop the leak and get the unit dry. (I am fully aware of the miraculous bonding properties of this epoxy)

If successful, I will spend the $300 on gas or fat sacs that would be more gratifying. Yahoo.gif

Thanks for the help. I'll let you know if it worked when I get it done and take the Bu out for a spin.


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If successful, I will spend the $300 on gas or fat sacs that would be more gratifying. Yahoo.gif

Exactly my thoughts. Biggrin.gif

I would be suprised if you couldn't fix the cracks with JB Weld. Be sure to get ALL the water out of the system...

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I didn't quite understand where/how it was cracked. A picture would really help. But from what I could understand it sounds like you could seal it up. Marine RTV (ie. silicon) should work. To answer one of your original questions: no water should be in there or even up in the lines. The gauge works off of air pressure due to the water pushing on it at speed. If you have a completely sealed system then water will never make it up to the dash. If you have a small air leak then you will eventually have a small water leak. I'd try sealing up around the crack with silicon then reattach the hoses - make sure to wire tie them tight and see if it works. No need to replace the unit without giving it a try. Good luck.

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Mine gets water in it and never leaks...and it will freeze every winter if I do not remove it. When I do, you can shake it and a very small amount of water will drip out of it. :(

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  • 6 years later...

I realize this is an old thread, but I have water leaking from the MDC, which I have stopped by disconnecting the pitot tubes. Pistol "replacement part on hand" Pete says to replace the MDC, others suggest I can wait. I am not that concerned with no speedo this summer, but need the rest of the gauges.

Anyone have a MDC fail after a water drip?


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  • 3 weeks later...

Mine failed first run of the summer yesterday. Worked fine skiing up to 32 mph. Did a speed run to finish the day and bam...water starts spraying on my knees. MDC housing is cracked near where the lines enter the unit. So question is did it freeze and crack over the winter or did the high speeds (45mph) stress an older unit and cause brittle plastic to break? The boat is a 2001 Malibue Response LX.

Regardless, I now have no working guages on the instrument display. They all froze mid run with temp at 158, oil pressure around 60, 13 volts and 3/4 tank of fuel. I've got the unit off trying to dry it out in a bag of rice but not sure I'll get my guages back.

Of course, wouldn't you know it's 95 and sunny here in VT which doesn't happen to often. I've already disconnected the speedo lines at the transom and tested the boat without gauges and everything works fine so I guess I could run it without until I get this squared away?

Anyone know where to find a good deal on new MDC?

Or better yet a fix, or know which pronge on the plug is the power source as I've heard MDC will fail if not getting full 12volts. Although I'm pretty sure the water is the culprit. Thanks!

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