Temp gauge reading strange

[FuzzDaddy]

Hi everyone!

I still have the boat home doing maintenance things. When I run the boat with the hose muffs on the temp gauge stays at 100 with the engine running. After I run it for 5-10 mins it still says 100. I turn the key off and back to the on position without starting the engine and it shoots up between 150 and 170. If I start the boat the temp gauge moves to 100. Why does the gauge only read when the engine is off with key in the on position?
Thanks for your time!

 

[FuzzDaddy]

Here is a pic of the temp gauge

 

[Chip S]

Water from a garden hose is typically pretty cold. I've never been able to get my engine up to temperature running on a garden hose.

 

[FuzzDaddy]

Hi Chip,
So basically the garden hose is to cold when running through the engine. So when the engine is off the water pump stops and just heats up the water in the block on its own?

 

[scoflaw]

Should come up to temp on a hose. What T-stat is in it ?

 

[Chip S]

Hi Chip,
So basically the garden hose is to cold when running through the engine. So when the engine is off the water pump stops and just heats up the water in the block on its own?

That's been my experience. On the hose my engine runs around 105 but in the water it runs around 160.

 

[FuzzDaddy]

I’m not sure. I didn’t take it apart to check. Since it reads with the engine off key on could it be a wiring issue? Or is it normal for the engine to spike when you shut it off? Could it be possible the thermostat Is backwards?

 

[scoflaw]

More likely, you have no t-stat If you have a stat no water flows through the engine until it opens. So cold hose water has nothing to do with it.

 

[Chip S]

I’m not sure. I didn’t take it apart to check. Since it reads with the engine off key on could it be a wiring issue? Or is it normal for the engine to spike when you shut it off? Could it be possible the thermostat Is backwards?

It's normal for the engine to spike when you turn the engine off. That's why it's recommended to idle for a short time before shutting the engine down.

 

[FuzzDaddy]

All good points! Also maybe I don’t have a thermostat? Is it ok to run without one?

 

[R-and-R]

Seems likely that your t-stat is stuck in the open position. Not a huge problem, but worth fixing.
Cheap and easy to replace.

 

[scoflaw]

Engine runs more efficiently at 160. You need your oil to get hot to burn off condensation that accumulates

 

[Soulshine]

All good points! Also maybe I don’t have a thermostat? Is it ok to run without one?

Running without a thermostat means you’ll be running at far below normal operating temp.

That can create a rich fuel mixture condition, carbon buildup in the cylinders and fouled plugs.

 

[FuzzDaddy]

I did notice some water in the oil
Maybe it’s condensation from the engine not running up to temp?

 

[scoflaw]

Yup, get a stat and a gasket. Easy fix.

 

[FuzzDaddy]

Well I just pulled the thermostat housing and bam!!!! No thermostat! I’ll pick one up tomorrow. I know I’m not in the clear with the water in the oil but I sure hope installing a thermostat helps or solves the problem!!
Job well done everyone.
Thanks for the help!

 

[Soulshine]

You have to wonder why there’s no thermostat in there.

The reason I mention this is my last boat ran so cool when I bought it that the gauges didn’t register anything at all. They tested as functional though so I looked further and found no t-stats.

Soon after installing them I had overheat issues caused by obstructed manifolds. The manifolds were snotty looking and replacement was planned from the get go.

The PO took the t-stats out to keep it cool.

The carbs were leaned out to compensate too. It seemed like just doing the manifolds was too much trouble for him so he employed many layers of repairs to avoid it.

 

[FuzzDaddy]

Oh boy. Maybe I’ll get lucky. I’m glad to hear that be be my issue with water in the oil though. Are there different temp thermostats or only one? I’ll get a thermostat and see what happens. What are the normal recommend temps running with a thermostat?

 

[Espos4]

Usually 140-160°
Depends on the gear of your motor. Check your motor number against the mercury online parts Manual.

For salt water cooled 160° max as the salt crystallizes more easily at temps higher than that.

 

[FuzzDaddy]

Thank you very much for all the info. Since I mentioned I had some water in the oil which could be because of not having a thermostat, how much condensation could be caused by running at lower temps without the thermostat? I’m probably making a big deal about nothing but I thought I should ask. I would like to know so I can keep a eye on it.