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Volvo Penta 5.0 GXi-D overheating

N

Nuddzy

New member
Hi, I really need some help to solve an overheating problem on my Four Winns 225 Sundowner. The power unit is VP 5.0 GXi-D with Duo Prop, sea water cooled, has approx 300 hours on.
The engine runs well, and does not overheat below 2000 RPM. However, above 2000 RPM it seems to overheat, the gauge goes right up and the alarm sounds. When I back off and try to accelerate the engine will not increase revs, so I assume it enters limp home mode.
There does not seem to be any evidence of it actually being hot, with an infra red thermometer on the thermostat housing it only reads approx 162 degrees fahrenheit. No steam, no burning paint, doesn't smell hot etc. All hoses look good inc. the rubber hose from drive unit into transom.
Ive experienced this fault since the engine was serviced. 2 spark plugs had corroded in starboard head and so the head was removed so to they could be removed and replaced. Its had new plugs & leads, new fuel pump, temperature gauge, temperature sender, water pump, thermostat, impeller, starboard exhaust manifold. (as old one was corroded) New impeller has been checked and is fine; the starboard riser was clear when head was removed and exhaust manifold replaced.
Water pump does not feel hot when engine has overheated.
Overheats when its on the plane or not on the plane, but only at over 2000 rpm.
Does not overheat when in neutral and being revved to 3000 RPM+
Any ideas what could be causing this, really struggling to know what else to try. Boat is in the UK and used on the sea; its kept on trailer and flushed with fresh water after every use. Starts and runs fine, apart from this!
Thanks for reading and if you have ideas please take a couple of mins to give suggestions.
 
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In this schematic, SEQ #8 is a temperature sensing unit that will trigger an over-temp alarm if either senses heat above it's range.
It's unlikely that both would fail simultaneously, but nonetheless you may want to test them.



19882.jpg
 
thank Rick. is there any relation between the engine temp sender and the overheat sensors? Or do i have 2 separate reporting systems telling me the same thing, i.e. the gauge/alarm and also the ECU kicking into limp home as a result of the exhaust riser overhear sensors. could it be an electrical fault at all?
 
I do primarily the AQ series. However, I believe that the temp sensors in the exhaust elbows report to the ECU/ECM, and are what trigger the over-temp alarm.


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The buzzer alarm is triggered by either of the exhaust elbow sensors and also coolent temp and oil pressure.
In your case if you can see the temp gauge going off the scale then it probably is a faulty sensor.
The ECU does go into limp-home mode and a DTC will be set, which can be read by a diag tool
The problem is that the ECT sensor cannot just be disconnected as this will trigger a fault condition according to my electrical schematics.
I would replace the ECT sensor and see what happens.
 
Could be Lower unit outdrive raw water pick up Tube seal is bad or the seal between the lower unit and gimbal housing. When you get on plane the seal has a hole or tear and raw impeller pump sucks air instead of water because the seal is above the waterline on plane. No water is then pump thru the engine and manifolds and then over heat . But you said overheats when not on plane also.
 
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Hi Kccoe, could you give me a brief description on how to make the repair you mentioned above? I’m almost positive that is my problem. Do you have to remove the stern drive to get that inlet hose? Seems like a tight space! Thank you in advance!
 
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