Volvo 5.0GXI Overheat/New thermostat

[scfdbc9]

Had a post up yesterday about this boat overheating…. Tried to modify it but was giving me a fit so I created a new post.
Meant to include that i replaced the thermostat prior to the overheating incident. Several local car guys who I trust nodded their heads when I told them of the “crisis” but said to confer with some boat guys to be sure.

What do you guys think? Faulty, new thermostat, stuck in closed position causing water to dead head and not circulate through motor and out exhaust/bellows area or something else still?

For the uninformed, motor would not come up to temp on hose pipe water into flush inlet but risers were super hot…. Almost seemed like water temp gauge was faulty. Once boat was dropped into water off lift the temp gauge seemed to react but went really high and threw over heat alarm….

 

[Scott06]

Had a post up yesterday about this boat overheating…. Tried to modify it but was giving me a fit so I created a new post.
Meant to include that i replaced the thermostat prior to the overheating incident. Several local car guys who I trust nodded their heads when I told them of the “crisis” but said to confer with some boat guys to be sure.

What do you guys think? Faulty, new thermostat, stuck in closed position causing water to dead head and not circulate through motor and out exhaust/bellows area or something else still?

For the uninformed, motor would not come up to temp on hose pipe water into flush inlet but risers were super hot…. Almost seemed like water temp gauge was faulty. Once boat was dropped into water off lift the temp gauge seemed to react but went really high and threw over heat alarm….

Take out the thermostat and test it in pot of water on the stove.
what is the condition of the raw water impeller ? Also i think there is a plastic fitting on the transom housing that the hose bringing water up from the drive attaches to that can break

 

[dubs283]

what is the condition of the raw water impeller ?

This is the cause of 99% + overheat/cooling issues on a marine engine

Ratio of sea water impellers replaced vs thermostats for overheat is greater than 100:1

 

[scfdbc9]

Take out the thermostat and test it in pot of water on the stove.
what is the condition of the raw water impeller ? Also i think there is a plastic fitting on the transom housing that the hose bringing water up from the drive attaches to that can break

Raw water impeller was swapped as well and is brand new.

 

[scfdbc9]

This is the cause of 99% + overheat/cooling issues on a marine engine

Ratio of sea water impellers replaced vs thermostats for overheat is greater than 100:1

Thats what Im hearing/reading as well. I swapped impellers at the same time as the thermostat. I checked it after overheat and it was in good condition.

A local boat guy suggested pulling the line that comes from the water pump into the thermostat housing and checking for water flow at the housing with the boat running. I tried that and had zero water coming out at the top of that water line.... in fact, I even pulled the line off at the water pump and had very little, if any water coming out of the water pump outlet. Does that offer any help?

 

[dubs283]

A local boat guy suggested pulling the line that comes from the water pump into the thermostat housing and checking for water flow at the housing with the boat running. I tried that and had zero water coming out at the top of that water line.... in fact, I even pulled the line off at the water pump and had very little, if any water coming out of the water pump outlet. Does that offer any help?

This is good advice and good information, it suggests one of two things. Either the hoses are installed incorrectly on the pump, i.e. intake/output swapped. Or there is a restriction before the pump. Best to backflush from the pump out the drive and inspect for blockages

One other scenario is if the shaft on the pump is keyed the key may be missing. Hopefully you've used oem or comparable quality for an impeller

 

[scfdbc9]

This is good advice and good information, it suggests one of two things. Either the hoses are installed incorrectly on the pump, i.e. intake/output swapped. Or there is a restriction before the pump. Best to backflush from the pump out the drive and inspect for blockages

One other scenario is if the shaft on the pump is keyed the key may be missing. Hopefully you've used oem or comparable quality for an impeller

I suspected water lines as well but have not had them off at same time to get them crossed.

Can you educate me on backflushing from the pump? Or point me to a link or video? Thx for the help....

 

[Scott06]

Can you educate me on backflushing from the pump? Or point me to a link or video? Thx for the help....

Take the water inlet hose off the pump- the one that comes up from transom housing , hook a hose up to it a flush backwards to water intake in drive full flow of water should come out. Look for any leakages or reduced flow. Any thing that leaks going backwards likely sucks air. Also could have the PS cooler plugged...

 

[scfdbc9]

Take the water inlet hose off the pump- the one that comes up from transom housing , hook a hose up to it a flush backwards to water intake in drive full flow of water should come out. Look for any leakages or reduced flow. Any thing that leaks going backwards likely sucks air. Also could have the PS cooler plugged...

OK. That hose should be the one that has the T in for the garden hose connection, correct? So unhook that line and flow water from water pump end. Water should then come from the foot and the exhaust area round bellows?

 

[Scott06]

OK. That hose should be the one that has the T in for the garden hose connection, correct? So unhook that line and flow water from water pump end. Water should then come from the foot and the exhaust area round bellows?

It will not come out the exhaust only the water intake ports in the drive
I would assume it is the hose that has a flush port on it but I'm not looking at your boat... One of the hoses to the pump will go up to the thermostat housing the other will go back to the transom housing - the one that goes back to transom housing ...

 

[scfdbc9]

It will not come out the exhaust only the water intake ports in the drive
I would assume it is the hose that has a flush port on it but I'm not looking at your boat... One of the hoses to the pump will go up to the thermostat housing the other will go back to the transom housing - the one that goes back to transom housing ...

yes it does have the flush port. When I plug into it, I get water out of the foot. Does that serve the same purpose as what you are asking me to do or will flowing straight into the hose at the water pump cause it to react differently?

 

[Scott06]

yes it does have the flush port. When I plug into it, I get water out of the foot. Does that serve the same purpose as what you are asking me to do or will flowing straight into the hose at the water pump cause it to react differently?

It does as long as no flow is going past the pump not sure if it will hold back the water and force it towards the drive

 

[Lou C]

If this is an SX drive there is also a clean out on the upper gear housing that you can open up by removing the plate over it after removing the plastic cover for the shift linkage.
Sometimes a used impeller can look good but not pump so well. If you ever sucked up sand it can grind up the sides of the fins and also the wear plate in the pump. I had that happen once after a soft grounding. I change impellers every 3 seaons or so.

 

[BRICH1260]

You need to make sure the pump is pumping first. Hook up the hose and turn on the water after loosening the thermostat intake hose. Start the motor briefly and pull the thermostat hose, is water being pumped out? turn motor off. If not, your pump is not working properly. If it is, then check the manifold feeder lines at the thermostat. Start the motor again and pull those hoses one at a time, is water being pumped out? Just do not let motor run long, just a few brief seconds at a time.

If all is good up till now, pull thermostat and check it in boiling water. Run without thermostat to see if water exits exhaust, if not, your manifold and risers may be clogged with corrosion.

 

[scfdbc9]

You need to make sure the pump is pumping first. Hook up the hose and turn on the water after loosening the thermostat intake hose. Start the motor briefly and pull the thermostat hose, is water being pumped out? turn motor off. If not, your pump is not working properly. If it is, then check the manifold feeder lines at the thermostat. Start the motor again and pull those hoses one at a time, is water being pumped out? Just do not let motor run long, just a few brief seconds at a time.

If all is good up till now, pull thermostat and check it in boiling water. Run without thermostat to see if water exits exhaust, if not, your manifold and risers may be clogged with corrosion.I

I get nothing at the thermostat housing with boat running and hose water on. In fact, I unplugged the same hose at the water pump itself and got very little water coming from the outlet there either. Water is coming from the intake ports of the motor but that’s it

 

[BRICH1260]

If you are using the blue cap flush port for water supply and you are getting no water up to the thermostat housing, then you have a raw water pump issue. Perhaps you have an air leak, check to make sure that your O ring is in place and that the vanes are not damaged.

 

[scfdbc9]

If you are using the blue cap flush port for water supply and you are getting no water up to the thermostat housing, then you have a raw water pump issue. Perhaps you have an air leak, check to make sure that your O ring is in place and that the vanes are not damaged.

Would the air leak need to be between the water pump and water intake or could it come after the water pump?