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Old 09-16-2015, 11:08 AM   #1
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Lehman 120 - false temp and oil pressure

With navigation electronics on, the water temp will climb and max out on the gauge, max indicated 220deg F. Which occurs with 2 VHF, 2 small MFD, 18" radar, auto pilot on. If I power off electronic items the water temp gauge will drop to approx 190deg, which is 10-15 deg above actual. The oil pressure gauge has the same issue, but indicates very low pressure.

Actual engine temp is normal, monitored with heat gun. Water coolant tank temp is approx 175 deg.

What is happening and what can I do to remedy?

CHB 34, single Lehman 120.

Thanks in advance
Dave
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Old 09-16-2015, 11:14 AM   #2
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Greetings,
Mr. w. The first, easiest and cheapest thing to do is check your ground connections on all instruments/senders and electronics right back to the battery(s) and beware of "daisy chaining" with the attendant connections.
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Old 09-16-2015, 11:22 AM   #3
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Old 09-16-2015, 12:02 PM   #4
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Most likely the power wires and/or the grounds for your electronics are mixed in with your gauges. Look at where the grounds and power wires for your electronics terminate.

We're the electronics installed by a professional or a DIYer?

Do not run all the ground wires directly back to a battery terminal. There should be, or install, a dedicated remote battery ground post for things like that.
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Old 09-16-2015, 12:06 PM   #5
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Greetings,
Mr. 11. HAH! Professional....?
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Old 09-16-2015, 12:13 PM   #6
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Quote:
Originally Posted by RT Firefly View Post
Greetings,
Mr. 11. HAH! Professional....?
If your asking a question, the answer is if they were installed by a professional you have a higher likelyhood of the installer following proper wiring techniques than a DIYer.

No guarantee perhaps. But the odds are at least in your favor.
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Old 09-16-2015, 02:05 PM   #7
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I installed a new radar, VHF, MFD, auto pilot, backup GPS unit. However, the engine gauge issue existed prior to my updates. And all the electric updates to date have been a simple swap out of old equipment, patching into existing power runs. The boat had existing cable runs and breakers for all of the above.

The boat is several generations of DIY. I'm slowing removing and replacing things like, wire nuts with crimp connectors. The shower sump wires spliced with electrical tape. Nothing is labeled, there are posts on the terminal block with 4 wires attached to a single pole. AC runs to duplex outlets with single strand romex cable.

I want to rip out everything and start from scratch, new panel, new terminal blocks, new runs, labels, but all at once is just not practical.

Can anyone suggest a single marine electric book with example fuse and terminal block layout for a boat with multiple banks?

I'll start tracing the gauge and nav electronic ground runs.

Thanks
Dave
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Old 09-16-2015, 03:20 PM   #8
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There are several good books. This is one of them.

Boatowner's Illustrated Electrical Handbook: Charlie Wing: 9780071446440: Amazon.com: Books
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Old 09-18-2015, 05:19 PM   #9
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Ordered the book, thanks. I'll post an update once I've made progress.
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