Overheating / temperature sending unit?

[RD9]

5.7l 350 mpi horizon mercruisrr 2003. 
 

my port motor as soon as motor gets to 3500 the over heating sensor alarm comes on not running just below this the motor will run as normal. I’m getting water because the top of the motor stays cool and have coolant.   Gauge is reading under the overheating mark. 
 

I did some research seems like temp sending might be issue. Anything else I could look at? Or suggestion?

 

thanks in advance guys. 

[lost a lure]

Impeller or heat exchanger fouled?

 

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[L&M]

I'm assuming it's twins, switch senders from one to the other and see if the starboard engine does the same with the port sender in it . Not often they go bad but it could save a lot of needless time & $ in the end.  

[RD9]

It is twins but each motor has a different sensor. I originally thought impeller but I have water, maybe it’s just getting week. 

[RD9]

4 hours ago, lost a lure said:

Impeller or heat exchanger fouled?

 

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Thanks for response it’s on a 3000 exspress pursuit impellers flat out suck to exchange. 

[Bozeman Bob]

I would get a infra red with laser light and compare the two engines over varying speeds. Had a burning smell we couldn't figure out , turned out to be the rubber hose coming off the exhaust manifold. The Temp gauge was always ok because it ran off the top of the intake manifold which was part of the closed cooling system. The exhaust was not part of that reading and the raw water elbow going into the manifold was blocked up with crud , the heat gun showed it.

 

[Sk8man]

I should think hanks advice should be the first and most straight forward thing to try before getting too far down the pike

[Bozeman Bob]

4 minutes ago, Sk8man said:

I should think hanks advice should be the first and most straight forward thing to try before getting too far down the pike

OP just stated the sending units were different

[Sk8man]

Ah I didn't see that Thanks Might want to have my glasses handier next time

[RD9]

On 3/27/2020 at 10:54 AM, L&M said:

I'm assuming it's twins, switch senders from one to the other and see if the starboard engine does the same with the port sender in it . Not often they go bad but it could save a lot of needless time & $ in the end.  

I got you I first read this post incorrectly. Thank you that’s good advice. 

[RD9]

On 3/27/2020 at 6:17 PM, Bozeman Bob said:

I would get a infra red with laser light and compare the two engines over varying speeds. Had a burning smell we couldn't figure out , turned out to be the rubber hose coming off the exhaust manifold. The Temp gauge was always ok because it ran off the top of the intake manifold which was part of the closed cooling system. The exhaust was not part of that reading and the raw water elbow going into the manifold was blocked up with crud , the heat gun showed it.

 

Thank you I have read about issues in manifold. 

[sherman brown]

my guess is the impeller is getting bad. pushing some water but not enough at higher rpm's.

[lakebound88]

I had this happen on my crusaders. Was just my sensor after verifying with my temp gun... replaced it an never returned. Good luck!

You also stated alarm, is your alarm also linked with oil pressures too?

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[RD9]

23 hours ago, lakebound88 said:

I had this happen on my crusaders. Was just my sensor after verifying with my temp gun... replaced it an never returned. Good luck!

You also stated alarm, is your alarm also linked with oil pressures too?

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It is but I have an oil pressure gauge on dashboard. I’m replacing impeller will it’s in yard and temp sending unit. Impeller If not needed to be changed will end up needed to be changed at some point. Better now then while out on lake.