Oil pressure and Temp not working

[oceanj]

Wanted to see if anyone ever had an issue with bad readings. Changed wires and guages and sensors but still getting a high reading. Thanks.

[cukes]

A LOT OF TIMES WHEN THEY FLATTEN OUT THERE IS A PROBLEM WITH THE GROUND

[oceanj]

It reads high same with the temp gauge.

[Duffman]

What are you working on? Inboard, I/O, outboard ?

And by “reads high” do you mean both gauges are pinned at there top end?

You replaced sensors, wiring and gauges ? What wiring? Both the signal feeds and grounds?

[Capt. Debbie]

99% likely the ground with a dirty connection. Especially with two different signals both screwed up

Those gages read millivolts. A voltage drop across a shit ground connection will do that.

The whole boat electrical system has the same assume ground reference to measure voltage against. Whether millivolts or volts. And if there's a slight different is the ground at one point versus another the small signal stuff is F'd.

Ever hear of stray currents at a dock? That's exactly it. AC ground carried out to the boat, may not be exactly 0.0 VAC when compared due to a dirty ground carrying connection. Boats with chargers - the underwater running gear O/B's, outdrives and Prop shafts are all connect to the motor and the ground. Still no big deal. Separate system. Then connect shore power including battery charger and the underwter running gear has the dock AC power 0.0 VAC ( or not with degraded dock AC wiring).

So if it's 0.0VAC at the bulkhead and your boat's ground is 1.5 VAC ( for example) higher- you will be electricity in the water. Very high electrolysis and if high enough you can feel it in the water. If even higher you can be electrocuted.

A boat you're dealing with relatively low and DC voltages of 14vdc or signal grade- mvolts. So the ground connections everywhere should be the same. SO to test measure ground at Neg battery post and ANYWHERE else. The should all be 0.00 vdc. If not---- you have a shit ground connection somewhere.

I hope this helps?

[oceanj]

Thanks. Will check the ground.

[oceanj]

Twin 350 merc inboards. Doesn't pin just higher than it should be for both.

[Capt. Debbie]

Same thing. Crapped up connections on multiple readings are ground voltage differences,

TEST:
Run a decent gauge wire from engine block to the instrument ground at dash. Essentially your ensuring the block 0vdc is the instrument panel 0vdc. Remember these gauges are reading milli-volts. AKA 1/1000 of a VDC

Originally Posted by oceanj

Twin 350 merc inboards. Doesn't pin just higher than it should be for both.