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Engine temp

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swilliams View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote swilliams Quote  Post ReplyReply Direct Link To This Post Topic: Engine temp
    Posted: August-25-2018 at 1:32am
My brother was telling me that while on his vacation he took out my Martinique for a spin and noticed that the engine temperature was at 160 degrees on the gauge and that it is closer to 180 degrees normally. After his return back to the dock he found that the alternator belt had broken. Got that all figured out but what stumps me is why it runs cooler without the alternator running. Does that really create that much more demand on that engine. The only other thing running is the rwp and that’s on a separate belt. Any ideas? Omc 350, 260 hp.
1976 Martinique,350 Omc. 1975 Glastron/Carlson CV16,115 Merc.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: August-25-2018 at 7:25am
Steve,
The engine wasn't running cooler. The voltage was low without the alternator causing the gauge to read low.


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Keep it original, Pete
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swilliams View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote swilliams Quote  Post ReplyReply Direct Link To This Post Posted: August-25-2018 at 9:09am
Boy do I feel stupid! Makes perfect sense. Thanks Pete
1976 Martinique,350 Omc. 1975 Glastron/Carlson CV16,115 Merc.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: August-25-2018 at 9:36am
Steve,
You shouldn't feel that way. It's just a case where your thought went the wrong way.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: August-26-2018 at 10:59pm
After reading this post and the answer, I have to admit I'm a little confused.

What's got me confused you wonder?

Pete says that the lower voltage due to the alternator not working was responsble for the drop in indicated temperature.

It's easy enough to check this out so I go out and check to see if indicated temperature drops when I disconnect the alternator and it does.

It dropped a few degrees(not nearly 20 degrees though)

It was at a rock solid 140 on the gage with 14.6 volts measured with a multimeter with the alternator functioning.

Disconnected the alternator with the engine running and ran it for quite some time till voltage dropped to 12.0 and I'd have to say temperature on the gauge said 136 to 137 as an estimate.

An IR gun told me that actual temperature never changed

So it seems that I agree with Pete's answer and could duplicate Steve's situation with the exception of the difference in indicated temperatures being a lot smaller

Now for the problem..............as long as CCF has been around people have asked questions like why does my indicated temperature go up when I turn on my lights or the blower or any large electrical load

The popular answer has been "because of poor dash wiring and grounding when you turn on the lights voltage drops and the indicated temperature goes up"

So..........
in the first situation voltage going down made indicated temperature go down

In the second situation it's being said that voltage going down made the indicated temperature go up

Only one of those answers can be right, so somebody needs to unconfuse me

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: August-27-2018 at 8:54am
Ken,
Maybe I can confuse more??
The unknown in Steve's scenario is the actual voltage. Maybe pretty low below 12? You only went down to 12. I don't feel the gauges read real linear to volts.

Gauges going up when a load is applied? Could be the alternator kicking in making more volts?

Then remember the basic gauge test. It pegs when the resistance of the sender is removed maxing out the volts.

We need some more testing!

One more interesting item is old gauges (not the case now) were dual coil due to the big voltage swings of generators. The needle movement was the mean between the full voltage unresisted coil and the lower voltage of the resisted coil. This is why old 6 volt gauges still read pretty close when electrical systems are converted to 12 volt.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: August-27-2018 at 9:37am
I already did more testing

I ran the gauge on 12 volts on the workbench in some 140 ish degree water and also on 6 volts and the indicated temperature dropped a little more but not 20 degrees.

Steve's boat wouldn't be running with 6 volts coming from the battery even with a set of points in the distributor, so I went well below any voltage that would have been seen by his brother.

You're one of the many people who have given the dash wiring answer over the years (easy to find on a search)

And yep a temperature gauge pegs high when the sending unit is grounded

So we're still agreeing that lower voltage gives a lower indicated reading.

And we're not coming up with a good answer for the temp gauge indications going up when the lights get turned on.other than "it's something to do with the voltage drop" which doesn't make sense or the grounding of the dash instruments is not good..

Maybe I'll go out and turn a good ground connection for the dash into a crappy ground connection under the dash and see how things act
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GottaSki Quote  Post ReplyReply Direct Link To This Post Posted: August-27-2018 at 1:36pm
yes, I also suspect a difference in potential of GND between the block and dash, could make the temp gauge go up,

Lights could pull a compromised dash GND high.   But blower is usually grounded near the tank or block, and would not have the same effect.
"There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing."

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Post Options Post Options   Thanks (0) Thanks(0)   Quote SNobsessed Quote  Post ReplyReply Direct Link To This Post Posted: August-27-2018 at 10:47pm
I too am perplexed on how a resistive circuit can act so screwy.

I looked at the wiring diagram & the only odd thing I can point to is pin 8 that must go to the alarm circuit. So could the alarm module be causing false readings?
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