Troubleshooting engine temp

[banderberg]

Next up on my list of things to fix, the temperature gauge, or thermostat?

I used an ohm meter to verify the temperature sender is working. My temp gauge on the dash never goes above 100.

Used a laser thermometer on the engine body and after ten minutes of idling the hottest spot I can find is 122 degrees F.

Considering pulling the thermostat next. Never done it before. Need to know how to tell if it's bad.

Any advice or suggestions?

 

[banderberg]

I pulled the thermostat, it's pretty rusted and seems seized up although i don't really have a good idea of how it's supposed to behave in my hand if I try to move it.

 

[Lou C]

It is not unusual with raw water cooling to have a stat that sticks open a little due to a rust flake very common with cast iron engines when raw water cooled. You can remove the stat (get a couple new gaskets first because they will just fall apart probably) and use an old style radiator thermometer to check if it opens and closes in a pot of hot water. If it's a 160 it will start to open at about that temp, the engine will run between about 155-165 with it, if its a 140 about 20 degrees cooler. Depends on what came on your engine. Make sure to use a marine stat, no car parts in there. They will rust up in no time.

 

[banderberg]

It is not unusual with raw water cooling to have a stat that sticks open a little due to a rust flake very common with cast iron engines when raw water cooled. You can remove the stat (get a couple new gaskets first because they will just fall apart probably) and use an old style radiator thermometer to check if it opens and closes in a pot of hot water. If it's a 160 it will start to open at about that temp, the engine will run between about 155-165 with it, if its a 140 about 20 degrees cooler. Depends on what came on your engine. Make sure to use a marine stat, no car parts in there. They will rust up in no time.

I put it in some CLR and brushed it clean with an old toothbrush and put it in a pot of boiling water. It opened up like this

 

[Lou C]

but does it completely close when the water cools off? If not then that's your problem, or at least could be it.

 

[banderberg]

but does it completely close when the water cools off? If not then that's your problem, or at least could be it.

It does now. I think it was stuck open before.

 

[dubs283]

It does now. I think it was stuck open before.

Stuck open because of age, debris, faulty?

If it failed once, it'll probably fail again. Testing for operation with boiling pot water is fine but if you remove a faulty thermostat best replace it with new and monitor operation

 

[achris]

I usually 'float test' thermostats.

Chris.....

 

[banderberg]

I usually 'float test' thermostats.

Chris.....

Thanks, not sure what that is. I'll see what I can find.

 

[banderberg]

Stuck open because of age, debris, faulty?

If it failed once, it'll probably fail again. Testing for operation with boiling pot water is fine but if you remove a faulty thermostat best replace it with new and monitor operation

It was rusty and dirty. I put it in clr and cleaned it up and tested it in boiling water

 

[Lou C]

Because this is such a common problem in raw water cooled engines in salt I usually replace them every 2 seasons or so. If everyone promises not to laugh I’ll share my “trick” for fixing a stat that doesn’t close because of rust flakes without taking anything apart…

 

[flashback]

Because this is such a common problem in raw water cooled engines in salt I usually replace them every 2 seasons or so. If everyone promises not to laugh I’ll share my “trick” for fixing a stat that doesn’t close because of rust flakes without taking anything apart…

I wanna know!

 

[Lou C]

Well…here’s what I’ve done. I leave a small hammer on the boat. If the temp starts reading low, I take the boat out and get it up on place for about 10 min then let it drop back to idle, before it cools off tap all around the stat housing to Create vibrations to loosen & flush out rust flakes. If that doesn’t do it just replace it. I’ve had this work a couple times over the years…..

 

[achris]

Because this is such a common problem in raw water cooled engines in salt I usually replace them every 2 seasons or so.…

Wow. I'm still running the original thermostat, 16 years old... (Yes, raw water cooled in the Indian Ocean)

 

[flashback]

Wow. I'm still running the original thermostat, 16 years old... (Yes, raw water cooled in the Indian Ocean)

Me too, 27 year old boat, 1 year in the Tennessee river. Who knows it's previous life..
But I will remember the trick....

 

[Lou C]

Chris my engine (short block & intake) are original 1988 used in salt over 20 years so maybe I’ve had more rust who knows, cyl heads were replaced 5 years ago

 

[achris]

Chris my engine (short block & intake) are original 1988 used in salt over 20 years so maybe I’ve had more rust who knows, cyl heads were replaced 5 years ago

I have a friend with a couple of (currently) 350s in a penned boat... Still original thermostats, engines NEVER freshwater flushed, boat launched in 1984.

I think your 2 year replacement policy is making someone rich, and it's not you...

Chris...

 

[Lou C]

When the start chronically sticking and it won’t get over 120* F I feel like I have to get it right. Still have the old ones so can re test & see if they are still good.
So Chris these boat are raw water cooled, in salt water all that time & no rust thru of the heads & block?
I know when I changed the cyl heads the cooling passages were getting eroded to the point that the machinist felt they wouldn’t seal right if the head gaskets were changed but upon further examination they found cracks due to a past overheat. So I changed them….I guess it all depends on how salty your water is….

 

[achris]

...So Chris these boat are raw water cooled, in salt water all that time & no rust thru of the heads & block?

Not what I said!

I know when I changed the cyl heads the cooling passages were getting eroded to the point that the machinist felt they wouldn’t seal right if the head gaskets were changed but upon further examination they found cracks due to a past overheat. So I changed them….I guess it all depends on how salty your water is….

Open bodies of sea water all have roughly the same salinity, 35g/litre.

Chris...

 

[nola mike]

Not what I said!

Open bodies of sea water all have roughly the same salinity, 35g/litre.

Chris...

Crap, I know mine in ppt. Is that a Yankee measurement scale as well?