Low Engine Water Temperature

[johnmsch]

I had a new 496 engine built for my 1994 Chaparral 2130, replacing the original 7.4L 0F282685. Although the motor is new, all the surrounding pieces were reused (seawater, fuel, power steering pumps, starter, etc.).

The first day I took it out, everything seemed to be running normally, including the water temperature gauge. The second day, I noticed that the temp seemed a little under normal at around 120. The third day, over about a 2 hour period, I could see the temp slowly going down to the point where the temp was barely at 100, which is the bottom mark on the gauge. I kept checking the hoses by hand and the pressure and temperature of the raw water and circulating water felt about right. Completely forgot to bring my infrared temp gun on the boat that day.

Yesterday I did some diagnostics. The thermostat housing has the temperature sender on the starboard side with a tan wire and the overheat alarm sensor on the port side with a tan wire with blue stripe. I took the tan wire of the temp sender and with the ignition key on, grounded it to the block. The gauge pegged on high so that means the gauge works. Although I've read that these temp senders rarely go bad, given that its 27 years old, I'm picking up a new one (806490T) from a local dealer. Also getting a new thermostat as I can't remember when/if I ever swapped that out. You guys agree with my line of thinking? Could there be anything else I'm missing?

Checking the overheat alarm sensor, I went through the same procedure, grounding the tan/blue wire on the block with the key on, but the alarm did not sound. I have traced both wires all the way back to the dash and don't see any issues. Shouldn't that procedure work with this sensor also?

 

[Bondo]

I had a new 496 engine built for my 1994 Chaparral 2130, replacing the original 7.4L 0F282685. Although the motor is new, all the surrounding pieces were reused (seawater, fuel, power steering pumps, starter, etc.).

The first day I took it out, everything seemed to be running normally, including the water temperature gauge. The second day, I noticed that the temp seemed a little under normal at around 120. The third day, over about a 2 hour period, I could see the temp slowly going down to the point where the temp was barely at 100, which is the bottom mark on the gauge. I kept checking the hoses by hand and the pressure and temperature of the raw water and circulating water felt about right. Completely forgot to bring my infrared temp gun on the boat that day.

Yesterday I did some diagnostics. The thermostat housing has the temperature sender on the starboard side with a tan wire and the overheat alarm sensor on the port side with a tan wire with blue stripe. I took the tan wire of the temp sender and with the ignition key on, grounded it to the block. The gauge pegged on high so that means the gauge works. Although I've read that these temp senders rarely go bad, given that its 27 years old, I'm picking up a new one (806490T) from a local dealer. Also getting a new thermostat as I can't remember when/if I ever swapped that out. You guys agree with my line of thinking? Could there be anything else I'm missing?

Checking the overheat alarm sensor, I went through the same procedure, grounding the tan/blue wire on the block with the key on, but the alarm did not sound. I have traced both wires all the way back to the dash and don't see any issues. Shouldn't that procedure work with this sensor also?

Ayuh,..... Yer headed in the right direction, I think,....
'n, Ya, the alarm works the same way,.....

Is there power to the alarm,..??

My WAGuess,..... The t-stat housin' has lost it's ground,.....
Silicone, wrong gasket, Whatever,....
In yer tests, did you ground the sender/ switch to the t-stat housing, or elsewhere,..??

 

[johnmsch]

Yep, the alarm works fine. When the key is left in the "On" position for more than about 10 seconds, the alarm sounds.
For grounding, I'm using an upainted side of the head of a bolt that holds down the thermostat assembly, which goes into the block. Since that works as a good ground for testing the temperature gauge, I would think it should work for the alarm ground also?