5.7 temp sensor

[Tunabass]

I noticed that since I’ve had the boat the temp gauge usually gets up to 180-200 despite having a 160 degree thermostat. Today I changed the thermostat and gaskets and sleeve and ran it on the hose. It still went up to about 180 before dropping. I grounded the temp sensor and the gauge spiked so that’s good. So now I’m thinking I may want to change out the temp sensor. Is this the right part number? [h=1]806490T[/h] serial number: 92022710 (reman from mercruiser)
mercruiser 5.7 EFI

thank you.

 

[alldodge]

I would suggest finding out if the motor is getting to 180 first. If it is, then there is another problem. Get a IR temp gun and measure the thermostat housing

 

[Tunabass]

I’ll have to do that in a few days. My gun is at my other house. But I’m on the boat right now running on the muffs and I can easily keep my hand on the thermostat housing even at the warmest it gets. What’s weird is that when the gauge is reading 180 that’s when the thermostat housing is the coolest. It gets a little warm when the gauge reads the lowest. And by warm I mean like holding a slightly warm cup of coffee

 

[achris]

On EFI engines the sender for the gauge is not the same sender used by the engine computer. If you have access to the diagnostic software, that can give you an actual temperature reading from the digital sensor.

The gauge and its sender are not calibrated instruments, they only give an 'indication' of the temperature. Being 15 or 20 degrees off is not unusual. Just be careful you're not chasing a fault that doesn't exist.

Chris. ......

 

[Tunabass]

Thanks Chris. Wonder if it’s worth trying a different gauge then just return it if it yields the same result. Boats getting its bottom blasted tomorrow and I’ll be away until Thursday so I’ll experiment then.

Theres no no way the thermostat housing gets anywhere near hot to the touch after 15 minutes on the hose though. Should it?

 

[alldodge]

The temp sender in your first post is the correct one.

Since you can keep your hand on the thermostat housing and you have tested the gauge, then the most probable cause is the sender

Also should add, don't know what year your motor is and the reman number cannot be looked up

 

[Tunabass]

Thanks Dodge. I’ll replace the sender. Should the thermostat housing be hot to the touch or are my finding normal in respect to the warmth of it? Thank you.

 

[alldodge]

The thermostat housing would be normally thethe temp of the thermostat or a little higher. The stat opens at its preset value expelling hot water and cooler water is pushed in by the circulating water pump and raw water pump. It being cooler then the stat setting would tell me its not yet fully warmed up being on a hose

 

[Tunabass]

I replaced the temp sender to the gauge and now the gauge will not go above 160 as it’s suppose to. Success. With my temp gun the only part of the thermostat housing that gets warm is the sides right where the thermostat is. The top of it never gets above 97. The sides read around 140-150

 

[alldodge]

What year is the boat?

 

[Tunabass]

1998 24’ Silverhawk

 

[alldodge]

Looked thru 97 and 98 and both should use the 4 port thermostat housing as seen below. I would say your thermostat is either not installed correctly or there is something which is allowing water to bypass the thermsoat

 

[Tunabass]

That is exactly how it’s installed. The new temp sensor now is accurately displaying temp that correlated to the 160 degree thermostat. It’s just that the top of the housing does not get hot. Just the sides do. Basically right where the arrow is pointing on your diagram is where is was taking the readings and getting 140-150 with the laser thermometer

 

[alldodge]

I think your good to go now

 

[Tunabass]

Thank you. I feel much better about it. Relatively easy and cheap fix too. That never happens...