Penta 5.0 GXi-E Cooling System issue/question

[Jwfinlan]

Hello all, I’m brand new to the forum and had a subject I can use some input on. I recently had an engine shutdown due to a high temp on the water. The thermostat was recently replaced as well as the raw water pump rebuilt within the last 15 hours. While at idle the temp got up around 220 and I had to shutdown the engine. We checked the inlet fins on the lower unit and no obstructions.

Since then I have pulled apart every hose in the cooling system and flushed, checked the clean out on the outdrive, as well as the raw water pump impeller, and thermostat. Water will run cleanly throughout the flush out with the engine off, and does push out through the exhaust with the engine running, I cannot get water to draw up the lower unit into the system at this point. Im sure this was my original issue while underway.

My last thought, and only component I haven’t troubleshot would be the Water Circulating Pump, item 19 in the diagram below. I don’t know if this is true but does the circulating pump help with drawing water up the outdrive fins in addition to the raw water pump? My next move is to pull this unit off and inspect, and for $200 I don’t mind swapping it, especially if that could be my fix.

Any help is greatly appreciated. Thanks
irculating Pump

 

[QBhoy]

You made sure the power steering cooler isn’t sucking air ?

 

[ESGWheel]

You rebuilt the raw water pump 15 hrs ago. Did it run OK (not hot) for all those 15 hrs and only now just started overhearing?

The circulating pump will not ‘draw water’ as it is a centrifugal pump and probably not the issue. The raw water pump should ‘pull’ water from muffs on the drive and if not, there is something wrong. One possibility, suggested by QBhoy above, is there is a ‘leak’ in the system allowing air to be sucked in vs. water by the raw water pump. Another place is the flush out plug. A friend of mine had overheating issues and finally realized his plug was loose. I have added checking it for being tight on my prestart up checklist (also make sure it has a good washer).

These engines are also funky in that the thermostat is held in place by item 3 vs. being ‘clamped’ by the t-stat housing. So possible it’s moved and now seated incorrectly.

Of note is that I also had an occasional overheating issue on my 2005 GXi-E at idle. I never found a smoking gun but issue was resolved when I simply replaced all the components: raw water pump, circulating pump, t-stat. Boating season (which is short in NE) overrode desire to nail down the root cause. Have had zero over temp issues in years since.

 

[QBhoy]

I may have missed you mention, but I don’t suppose the boat has a hot water domestic system, passively heated by a feed and return system, off the engine ? If it’s raw water cooled and it does feature this..I’ve a couple of times known this to be the cause of a loss of prime in the cooling flow. The heating coil piping the supply runs through (inside the hot water tank heater), had corroded through, allowing this to happen. Just thought I’d mention it. Probably not relevant here. If it is, it’s fed off the circ pump. Fittings for supply and return are on the pump casing and near or befind the t stat, into the top of the head (from memory).

 

[Jwfinlan]

You made sure the power steering cooler isn’t sucking air ?

I did not. It’s only one small line going in, and it looked like a sealed line on the ends, not sure how to troubleshoot that.

 

[Jwfinlan]

I may have missed you mention, but I don’t suppose the boat has a hot water domestic system, passively heated by a feed and return system, off the engine ? If it’s raw water cooled and it does feature this..I’ve a couple of times known this to be the cause of a loss of prime in the cooling flow. The heating coil piping the supply runs through (inside the hot water tank heater), had corroded through, allowing this to happen. Just thought I’d mention it. Probably not relevant here. If it is, it’s fed off the circ pump. Fittings for supply and return are on the pump casing and near or befind the t stat, into the top of the head (from memory).

Yeah, no heating coil. Boat is in warmer water as it is, always ran in Florida waters. Thanks for the input.

 

[Donald0039]

First when the raw water pump is on the engine like a Volvo Penta the engine will not pull water through the outdrive running on muffs unless you are using a garden hose which pushes the water under pressure into the outdrive.

The Mercruiser Alpha One has the raw water pump in the outdrive and can pull water in through the outdrive, it does not have to be under pressure from a garden hose.

I very much doubt the circulating pump is the problem. It's vanes are metal.

You can plumb some clear hose into the raw water cooling system to look for leaks.

I assume this is a RWC engine. No heat exchanger.

Cap on the flush port tight?

When the raw water impeller was replaced were all it's vanes intact?

Have you used an IR thermometer to check if the temp of engine, exhaust manifold and elbow/riser?

Temp sensor broken?

Check thermostat in pan of boiling water hung in it by string. Does it open at the proper temp.