Temperature Reading (Scratching my head)

[Rstorrie]

Cleaned and tested the temperature needle gauge on the dash, works fine. Temp Sensor on block was bad. Replaced it with a new sensor. Applied teflon tape to the threads, connected the sending wire and turned on the ignition switch. The temperature gauge immediately reads around 150* with a cold engine without starting the boat. Any ideas?

(Note: after letting it idle for about 10 minutes, the temp reading climbs and reads about 240* from the 150*)

 

[Scott Danforth]

first. verify your readings with an IR thermometer

second, if you get to 240, you have zero water flow and you burned all the rubber exhaust bits and probably scored your bores

third, when was the last time you did a PM on the raw water pump?

 

[Rstorrie]

I have not run the boat in water yet. I bought it and had to replace a couple parts. Idles smooth, water is shooting out the back of the outdrive with the muffs and in a tub of water. I looked all over the engine and do not see a raw water pump. 1987 GM Mercruiser 230 5.0 305cid V8. As stated, engine completely cold, turn key on, temp gauge immediately goes to about 150* on the gauge cold and not started.

 

[AShipShow]

How did you test the gauge to verify its working properly?

 

[Rstorrie]

12v getting to gauge, short sender wire to block, temp gauge pegs 240*

 

[wellcraft-classic210]

A few ideas

The sensor and gauge need to be compatible // some like autos & non Mercs can use different resistant ranges

I noticed you used Teflon tape which can act as an electrical insulator -- Were you able to verify that the sensor housing made a good electrical contact -- ( housing to block resistance check or voltage drop during use )

You may want to measure the sensor resistance and compare -- there are charts available for resistance at various temps.

 

[Rstorrie]

Where can I find a resistance chart for the Mercruiser 230 GM V-8 5.0L Alpha One?

 

[HT32BSX115]

Where can I find a resistance chart for the Mercruiser 230 GM V-8 5.0L Alpha One?

Howdy, Ordinarily I would say "GOOGLE is your friend"......but lately, that doesn't appear to be true!

So I did a DuckDuck-GO search, https://duckduckgo.com/?q= and found the following!
It'll open Adobe Reader if installed, or other PDF reader with the info you're looking for!

https://fariabeede.com/site_manuals/IS0085d.pdf

Cheers,

Rick

 

[altitude 411]

No Teflon tape . Permatex

 

[Rstorrie]

Ok, thanks..... I will give that a try

 

[AShipShow]

I doubt teflon tape is the issue unless you only put the sender in barely hand tight. When you put teflon tape on pipe threads, the high points tend to tear through the tape and jam it between the threads to help seal the clearance in the threads... If you take apart any pipe joint that has been tightened pretty much has no teflon tape left where the threads were touching.

Also, if the resistance was HIGHER than it should be, the temp gauge would be reading low, sounds like its reading too high... My guess is there is an issue with the sender itself (wrong part, defective, etc...)

 

[Scott Danforth]

If you tried to suck water up from a tub you toasted your impeller. The tub would have to be big enough to fit the whole boat to get the water higher than the pump to get it to prime

Always use muffs or put the boat in the water

So go back and now replace your raw water pump

 

[Scott Danforth]

I have not run the boat in water yet. I bought it and had to replace a couple parts. Idles smooth, water is shooting out the back of the outdrive with the muffs and in a tub of water. I looked all over the engine and do not see a raw water pump. 1987 GM Mercruiser 230 5.0 305cid V8. As stated, engine completely cold, turn key on, temp gauge immediately goes to about 150* on the gauge cold and not started.

The raw water pump is in the drive

You need to stop running the boat until you replace the raw water pump. You also need to now replace all the rubber bits in the exhaust that are now toast