Temp spikes when using trim controls, removed thermostat runs better

[ssquare14]

Volvo Penta 4.3GL PEFS
SX-M outdrive

Purchased my first (used) boat this spring and I have been struggling with overheating. When I purchased the boat there was water in the oil and other issues which I have concluded was from the previous owner leaving the plug in while on the trailer. I have noticed that the temp gauge dips slightly when moving the trim up or down.

I have since replaced the thermostat (which was toast), temp sender, impeller, changed the oil, checked lines for blockage, checked the lower unit inlet for blockage, and verified flow from the raw water pump by removing the outgoing line from the impeller housing. To combat the water in oil (which I suspect has something to do with overheating), I removed the risers and replaced with new gaskets.

I put the boat in the river today and after many frustrating hours I am still overheating. I removed the (new) thermostat and have been running much cooler, however there were times when it spiked until I moved the trim.

I know volvo has an overheating manual, but before purchasing the supplies necessary I was wondering if anyone has any ideas.

The thermostat was an oem 160 degree stamped thermo

 

[jerryjerry05]

The water in the oil?
It would have to be real deep in the boat to leak into the engine???
I'd guess a bad manifold/riser or oil cooler?
It's 15 years old and the manifold/ risers are probably due to be replaced???

Does it only overheat at higher speeds? Manifold risers.
The impeller how old?
The pump itself? What's it look like on the inside?
Any scrapes or deep scoring?
The cam plate can wear out.

 

[ssquare14]

Put it in the water at the boat launch and let it idle while we parked the trailer. 5-10 minutes of idle and the temp alarm was going off. Sometimes when I played with the trim level the temp would drop slightly almost as if I was un-blocking a clog or un-kinking the intake hose. I pulled it back out of the water, removed the (new) thermostat and dropped it back in the water - it ran a little cool, but good for the most part! So we stayed out on the water (granted half the day had wasted away at this point)

I replaced the impeller last week - no significant scouring on the housing. I also removed the risers, soaked with CLR and replaced with new gaskets. The engine has 175 hours on it so they were in decent shape.

 

[jerryjerry05]

175 hrs in 15years?
The rust or rotting goes on even with 3 hrs.
One time in salt water will start the rot fresh is a bit slower but still rotting away.

 

[ssquare14]

I am the second owner, so I can't give you an absolute but he said it was only used in fresh water as a lake boat. I think it spent a lot of time sitting and he said it was winterized. When I purchased the boat I test for compression and all cylinders were around 170. As for oil, the gauge reads on the upper hash mark for oil pressure at WOT.

Could a bad bellow be the cause? or improper thermostat?

 

[Bondo]

I have noticed that the temp gauge dips slightly when moving the trim up or down.

Ayuh,.... The only thing the trim pump, 'n yer temp gauge has in Common,....
Is their Grounds,....

You have a, or many failin' Grounds,....
Start at the battery terminals,...
Remove, clean to Shiny metal Clean, reinstall, 'n tighten,...
Then grease 'em to stop the corrosion,...

ALL the Grounds, both ends of All the Ground wires ya can find,...

 

[ssquare14]

Sounds like a tedious job!

So are you saying that temp gauge/alarm is getting false readings due to bad grounds? But why would removing the thermostat fix the issue? If the bilge did in-fact fill with water at some point in time, the grounds could certainly have some corrosion. What color wires should I be looking for - greens and blacks?

Also worth noting that the temp gauge was not receiving a signal from the temp sender (located on the intake) when I purchased the boat. I replaced the sender unit and I now have a temp reading.

 

[Bondo]

Also worth noting that the temp gauge was not receiving a signal from the temp sender (located on the intake)

Ayuh,.... Senders don't send signals, they measure varying resistance to Ground,.....
The gauge gets Power, the Sender varies the gauge's resistance to ground,...

'n as I said, the Only thing in common is the Grounds,....
Grounds could be black or yellow wires,...
Green is the bonding system, which is like a ground path, but ain't,....

 

[ssquare14]

Okay - I will investigate and report back