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nautacare

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I have a 1997 crusier twin 350

I have a 1997 crusier twin 350efi alpha gen II drives once im up on plane the temp gauge on one engine will get up to operating temp then fall eradictly-I replaced impeller and thermostat and switched sending units. I boat in fresh water on a river-could it be the gauge?
 
"could it be the gauge?&#3

"could it be the gauge?" Yes. But it may be a loose or corroded connection on the gauge. Remove the wire from the sender and ground it to the engine w/ignition on. It should peg the gauge. If not then you need to look at the connections on back. You could switch gauges to see if the problem follows the gauge.
 
I tested the gauge and its fin

I tested the gauge and its fine-I swapped gaugeand even jumped wiring to other engine still doing it-any more ideas?
 
Sure sounds like a wiring faul

Sure sounds like a wiring fault somewhere.
Suggest you pull apart the 10 pin barrel plug at the affected engine and carefully clean all pins and sockets.

Rod
 
Well I ruled out a wiring prob

Well I ruled out a wiring problem with the other engines wiring harness-I had the port engine running my starboard gauge and vise versa. This started last year-the engine ended up getting hot-the gauge never read hot-just moved around. This year I was running and this engine ended up dropping a valve seat-taking a piston with it. Had it rebuilt and the gauge is still wandering. But this is whats baffling me the gauge shows the engine coming down in temp-from about 145/150 to just above 100 then climbs a little and falls.
 
""...gauge shows the engin

""...gauge shows the engine coming down in temp-from about 145/150 to just above 100 then climbs a little and falls."

T'stat opening/closing will vary the gauge reading; more on some engines, less on others.

How much does it climb above 100 and how much does it fall? Do both engines behave the same?

Put a digital voltmeter on the AC scale and measure the AC voltage between the alternator output and the engine block ground. AC voltage should be no more than 0.005 volts. If it is greater there is a shorted diode in it."
 
The other engine is fine-the t

The other engine is fine-the tach wanders once in a while. My normal temp is around 145/150. I have a 140 t/stat in it. When it falls it gets about a needle width from 100 then will go up anywhere to 130/140 then fall.I did notice sometimes it stays around 110. If it was the diode wouldnt it mess with my other gauges? Ill use the voltmeter and see what happens Thanks.
 
"Don:

I reread all of your

"Don:

I reread all of your posts and am trying to come up w/some reason why the gauge behaves in the manner you have described. The changes in temps. indicate that the gauge is working as you proved by the gauge swap. They are also different compared to the other "good" engine. In order for the temp. sender to "sense" the changes occuring w/in the engine block it must make contact w/the cooling fluid continuously. The gauge will not sense air in the water jacket, hence the drastic drops in temps.

I suggest that you install a short piece of clear reinforced water hose on the water inlet side of the T'stat to determine if there are pockets of air or bubbles in the water stream coming from the OD. If you find air in the water stream, the repair lies w/in the OD. There were several threads that had your engine's problem this past year. The repair involved the water pocket at the bottom of the upper half of the OD. Good luck."
 
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