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Merc 8.1. At startup and low speeds mostly but occasionally on plane. Double checked all fluids. Runs well but continues to beep. Also, trim gauge not working but trim does work. Speedometer kicks in and out. Happened this weekend where it was working till the beeps started, then it stopped working for a while. Any ideas on what could potentially impact speedo during beeps?

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Hey ACB. Welcome to the Cobaltchat forum. So glad you found us!

Not the depth finder alarm correct? That has fooled others in the past. Especially if your engine doesn’t go into a reduced RPM limp mode.


The Merc speedometer is a simple system really. An opening in the lower drive unit allows water to channel in and compress air...which compresses a diaphragm on the speedometer making the needle move. Use a stiff piece of wire and make sure that pitot opening is clear. If there’s wood jammed in there a drill will work to carefully pull the wood out. Compressed air blown DOWN from the top of the drive can also dislodge the offending piece. Just remove the white plastic piece by turning it counterclockwise and pulling up slightly.

BTW,any pictures?

Again welcome aboard mate!

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Thanks For the quick reply AsLan7! I have cleaned out the port but didn’t blow down yet, will try that though. What worried me the most about is that it was working while driving @ 3k RPM or so, then got 6 beeps and the speedo went to 0. Later in the day it started to work again for a bit and then quit. Seemed to me like it may be some type of current issue but I’m not sure where to start to look. It runs fine with no noticeable performance lag either. Love the boat though.

That’s a good looking boat. Almost sounds like a faulty gauge. Need to hook a computer up to it and watch the vitals to know for sure.

Thanks! I figured I would probably have to get it hooked up. Cobalt dealer closest to me evidently won’t service It because it wasn’t purchased there so I may have to drag it over an hour away to have another dealer look at it. Hate that but want to get it fixed. Fingers crossed.

Wish they had a matching gps speedo. Download vessel view Mobil. It has a gps innit

I hear you. GPS speedo's fix a lot of design flaws right. Just took it to a local Cobalt dealer who is going to diagnose it in the next couple of days. Will report back what they find. Saying a couple of Hail Mary's and Our Fathers that this comes out to be little to nothing.

For future reference. The dealer came back with root cause as a trim sender malfunction. It was noted that the circuit that the sender is on is the same as the gauge cluster, thus could impact other functionality like the speedometer. The tech I spoke with felt that it absolutely could be where the short in the sender is pulling the circuit down to the point that there isn't enough current for all functionality to run, thus the speedo problem. Part is ordered and once installed I will verify a fix and comment again. This was quite frustrating given the additional issue with the speedo so I figured I would do my part and log the outcome to make it clear for others in the future.

A C of Blue wrote: Thu Aug 27, 2020 1:08 pm For future reference. The dealer came back with root cause as a trim sender malfunction. It was noted that the circuit that the sender is on is the same as the gauge cluster, thus could impact other functionality like the speedometer. The tech I spoke with felt that it absolutely could be where the short in the sender is pulling the circuit down to the point that there isn't enough current for all functionality to run, thus the speedo problem. Part is ordered and once installed I will verify a fix and comment again. This was quite frustrating given the additional issue with the speedo so I figured I would do my part and log the outcome to make it clear for others in the future.

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Thank you ACB....we love follow ups! (almost as much as we love pics) .... U da man. Keep us posted.