temp guage "wacky"

[surfjat]

hey gang, im new to this forum...but love the posts..im up here in narraganseet/wickford r.i........heres the problemo: when the engine is running the temp guage stays around 100 and doesnt budge. But when i shut the engine off, the temp guage needle goes to 140 and stays there until i go to start the engine again, then goes back down to around 100???????????????????????..im startin with cleanin all the connections in the bck of the temp guage..they are "green""....got this boat a pearson 30 last october.....ps....the water flow out the back of the boat is good...and engine runs super otherwise.....thanks for the help...jer...

[JOHN COOKSON]

Jer
To test the temp gauge:
Remove the wire from the sending unit and turn on the power. The gauge should peg low scale. Then short the gauge sender terminal to ground. The gauge should peg full scale.
This will test the gauge. You may also have a wiring problem or a sending unit problem(s).

TRUE GRIT

[smosher]

I have a temperature scanner and where the sender is is also where the water enters the head. The front of the engine runs cooler than the back on my A4. I do not have a thermostat, but a ball valve on the bypass. With the bypass closed, all of the water flows through the head, If I crack it open then some of the water bypasses the head. This tends to reduce the difference between front and back.

So I believe what your seeing is the temperature equalize with the engine off

I also have a P30

[bigal]

I have seen posts that using the ball valve in the bypass loop can control the engine temp better than the thermostat, how has the worked for you? I have a Pearson 36 with the A4 engine and have been running with no thermostat, but no valve on the bypass and the temp gauge runs cold about 120 at most.

[Bold Rascal]

Temp solution

Temp solution,,, get it?
My instruments are not all they should be either. getting them "right" is on my things to do list, so is retiring someday....
For the time being (as a TEMPorary solution) I went to pep boys and purchased an inexpensive set of auto gages, Oil Pressure, Water Temp, Amps. Yes I do have to step out of the cockpit on occasion to view them.

I have a P33, love it.

Good idea to check that water batching at the exhaust. I sure do..

[dvd]

New Temp Guage and New Sending Unit

The best thing to do is go to moyer on line and purchase a new sending unit and guage then you can cross these off the list. This is the best thing you can do with a new to you boat as the operating temp for the motor is pretty important. Always replace the temp sending unit and guage as a set.

Also, you need to realize that full operating temp on an A-4 is really not achieved until you have operated the motor under load for about an hour or even longer.

Good Luck with the new boat.

DVD

[Ball Racing]

I had a mechanical gauge that said I was always at 100 degrees unless WOT for a long time, then it would go up some.
I could feel the head at the sending unit area, and it was above my body temp I could feel.
I was stumped how it could not be more than 100.
So I put a electric temp gauge in there this weekend and now within the first minute of running you can see it start moving off 100, then after 5 minutes it's showing about 115 or so then after several minutes of WOT it goes 130 ish, and after a while longer the max I have seen is 140 ish..
Maybe thats not far off,the old gauge, but at least I see the movement.
And the higher temp makes sense.
The thermocoupling of the mechanical gauge just was not sesitive enough or something.

[J.Z.]

Fyi

Hey Surfjat,

I am also just south of Wickford harbor, off lone tree point. I have a 77 Tartan 30 with original A4, raw water cooled. If you need assistance, I have the moyer manual and tech update book. I enjoy working on the A4 and would be glad to lend them to you to browse or give you a hand troubleshooting. I am looking to find some t stat gaskets. Send me a note.....
jzcarver at gmail



Good luck and I will look for you on the water

John Z.

[jkmvenice]

Got to run the motor for a long time to reach operating temp. Anyone ever use a infrared temp sensor?

[sastanley]

infrared thermometers!

jkmvenice,

If you are talking about the trigger style available thru a place like Harbor Freight, than yes...I have..it works great all over the engine & its various parts.

I am waiting for my neighbor to return the one they borrowed for his son's science fair project, as I've just installed FWC, and would like to see the temps at the entry & exit points of the HX..

[JOHN COOKSON]

Got to run the motor for a long time to reach operating temp.

Is your thermostat stuck open? Is there crud around the sending unit?

TRUE GRIT