2021 G23 ZZ6 - Replaced Impeller - Engine Overheating

[Jgran]

Just replaced impeller on 2021 G23. Lowered boat into water on lift and ran at idle to check for leaks, etc. Engine temp kept rising to 200 degrees upon which I shut it off as to not overheat. While running I visually checked strainer and I couldn't see any indication of water moving, but strainer was clean and water is clear. Raised boat on lift and confirmed no obstruction to cooling water intake. Going to open up the impeller housing again and make sure that everything looks correct. Any input on other things I should be checking or what the best way would be to confirm water is circulating correctly? Boat ran fine with no temperature issues prior to impeller replacement.

[Jgran]

Opened up impeller housing and it was full of water and everything looks good. Now more confused…

[Scooter G]

Strainer full of water? Fresh water valve open?
On a 3+ season boat, unlikely that your thermostat is stuck closed or the temp reading is off, but anything is possible. Hard to mess up an impeller install. I have seen instances where the strainer cup is not properly seated (O-Ring/Gasket) causing a vacuum/suction breach.
Jimmy Neutron thinking here, I would pull the exit hose on the water pump to check that I had flow.
What was your winterization process, and what do you remember the normal operating temperature to be?
Do you have a fake-a-lake for an inland test to check water flow from the exhaust?
What did the old impeller look like, good, all vanes in their proper place?

[William_Zane]

To piggy back on what Scooter said. Make sure the Fresh water valve isn't open if you ran the hose through it.

[greggmck]

During the first day out after sitting for months the thermostat may open late. I would turn the heater blower on. This will extract additional heat from the engine. Continue to run it normally and the thermostat should open, dropping the operating temp rapidly down to 160 degrees. I often observe temps get up to 190 or so before the thermostat opens. Do not exceed 210 degrees.

[bturner]

The thing that bothers me on this one is that the OP is stating that he sees no water flow through the strainer. If that is indeed true then the problem is still at either the seacock or the pump. Even with the thermostat closed the pump should still be pumping water through the system, it just won't be going through the block.

My first take on something like this would be to go back to stupid and start picking off the basics. The first place to look would be where Zane suggested. I've seen it too often where someone (dealer or owner) has closed the valves during winterization and have even been guilty of this myself on my ballast pumps. If valves are open and there are no obstructions at the seacock, then the next place to look is at the pump. Here the basics would be... is the belt on the pump and is the belt correctly routed? On my motor you need to remove the belt during the impeller replacement process. If you try really hard, I would imagine it would be possible to either miss a tensioner or route it incorrectly. After verifying all the above I would pull the front plate on the pump (if you have one) and verify that the impeller is turning when the engine is rotating.

I worked on an Ilmor in a MasterCraft a couple years back that the owner stated it was overheating and could see no water flow. That pump was designed (for some reason beyond me) by Johnson pumps with a keyway on the drive shaft in the pump, that had fallen out when the owner replaced the impeller. It took me close to 2 hours to remove the pump from the bowels of the bilge, correctly diagnose the issue, find another key and replace the pump. On that one I used blue Loctite to "glue" the key in so it wouldn't fall out during the next replacement.

If the seacock is open, my guess is you have a pump or belt routing problem. At the end of the day this is how we learn.....

[greggmck]

How would any water be in the pump housing and strainer if the check valve were closed or the belt off the pump drive pulley?

[bturner]

Good question, he's the one that said he didn't see any flow, not me. Possibly the valve is barely open and he's getting very low flow? If there's water in the pump you'd think you'd see flow, right?

If everything is working as designed, then you move to thermostat.

[Scooter G]

I think it would be possible to still have water in the pump housing but not solid flow.
Don't we love blind diagnostics, funnest thing ever (not so much).
I knew this guy once that didn't check the impeller size against the old impeller, and he put the wrong one in. I won't mention any names. There was a little water flow, but not enough.

Alright Jgran, you got it all from some of the best seasoned vets above, make it happen, and let us know.
jpwhit might have something, but I think it's all been covered...

[Jgran]

Ok, thanks to everyone for chiming in with suggestions. Here are answers to the majority of questions: Strainer was full of water, fresh water valve has never been closed. Winterized by pulling 3 drain hoses and putting them at bottom of hull, emptied strainer cup and left off over winter, reinstalled strainer and put hoses on holder prior to launching this season. Old impeller was in pretty good shape, just general wear with no tears or missing pieces.

After opening the impeller housing and finding water and reading greggmck's suggestion to use the heater to dump more heat, I figured that I could go for a quick lake test not far from the dock to see if the problem recurs when underway. Headed out and the temp quickly rose to about 185 where I turned back towards home, as the temp got to 195ish it quickly dropped to 166/167 and then settled nicely around 170. I'm assuming that the thermostat is the culprit. I'll keep a close eye on it to see if opens late again when cold or should I just replace now?

[greggmck]

Glad to hear you are all sorted out. A late opening thermostat has been a common experience when taking my boats out for the first time of the season. I would not replace it unless you regularly see over 185 degrees when running the engine up for the day. My bet is it behaves normally going forward. Best.

[Scooter G]

HaHa good work team, greggmck nailed it!!!
I would say "again", but then his head would get all swoled.

Jgran, I could see your laser focus on the temp gauge, 193, 194, 195 - Thermostat opens, YES!

I'll keep a close eye on it to see if opens late again when cold or should I just replace now?

This would be a possible advantage of using antifreeze during the end of season shut down, some small lubricant factors involved here. Would it make a difference with a thermostat waking up, maybe. Do I use antifreeze, nada.