Overheating after impeller change

[Henno]

Hi all. First time posting, any help much appreciated.

Have a 1998 Four Winns Vista 248 with a Volvo Penta 5.7 GXI. Had a small leak in my water pump so I replaced the seals and impeller which looked in bad shape. Took the boat for it's first spin since replacing the impeller and noticed from the start the boat was running warmer that usual.(Usually runs at around 150F) it was running around 160F for about 30 minutes and then climbed to almost 200F at which point I shut her down. On checking everything it looked like the water was not even reaching the water pump. I managed to get water flowing through the inlet pipe to the pump and started her up again. I kept the boat under 3000 revs and limped home with temperature holding at around 170 degrees but as I approached the marina she almost reached 200 again.
So any ideas what could be the problem. Could it be an air leak and if so how to I clear this?
Just to stress the boat never went above 160 before now in the year I have had her. This problem has only presented after I removed the pump and changed the impeller.
Thanks in advance.

 

[kenny nunez]

Does your boat stay in the water? If so, there could be some marine growth in the supply side.

 

[Henno]

Hi Kenny
Yes it does stay in the water so maybe that is a possibility. I did get water flowing through by sucking on the pipe. I wonder if there was an air lock and I have now damaged the new impeller by running it dry?

 

[kenny nunez]

It will be a good time to inspect the impeller. You could try using a garden hose to back flow the water intake. Is the bottom clean of marine growth?

 

[MalibuMike]

Make sure the cap is tight on the water flush port.

 

[QBhoy]

Hi. Was there anything missing from the old impeller? Good chance you’ve maybe got part of it or the gasket stuck in the suction or discharge ports. Other than that, try bleeding the other water pump casing at the fitting there.

 

[Henno]

Make sure the cap is tight on the water flush port.

Thanks Malibu Mike. Not sure this model boat has a water flush port but I will check

 

[Scott Danforth]

did you put the hoses back on in the correct location?

 

[Henno]

did you put the hoses back on in the correct location?

Hi Scott. Yes the type of pump on my boat has two different size hoses on the inlet and outlet so you can't get it wrong. Thanks anyway

 

[Henno]

UPDATE
So today I checked the impeller and it looks perfect. I ran the boat in the water at idle for a good 20 minutes and it eventually reached a temperature of around 190F.
When I revved the engine the the temperature dropped to 160F approx it looked like I was getting a good flow of water. I continued to let it idle and the temperature rose again to around 190F.
Is it normal for an engine like this to reach 190F at idle?
Before changing the impeller last week my boat would normally idle at around 160F
Thanks all.

 

[Henno]

Just to add also. I noticed today also a marked difference in the temperature of the two risers. The port side remained only warm to touch but the starboard side was much hotter. You would not keep you hand on it for more than a second or two.

 

[kenny nunez]

If your engine still has the original manifolds I suggest they should be changed just for preventative maintenance.

 

[Monterey296Twin5.0Gi]

I am about to change impellers for the first time on new to me older 5.0L's. I opened one raw water pump and the housing and back plate were fairly worn. And it appeared that the old impeller had molded to that worn housing (still looked good and cooled well).

So I wonder about putting a brand new impeller into a housing with some wear, will it take time to "wear in" and not cool or pull water as well until it does? OR maybe it won't wear-in and the housing and back plate need machining or replacement? Did you notice any significant wear to the housing? Mine in pic below.

 

[dingbat]

May sound stupid, this is coming from an outboard guy, but did you also service the raw water impeller in the lower unit?

 

[Henno]

If your engine still has the original manifolds I suggest they should be changed just for preventative maintenance.

Looks like a good suggestion Kenny. I wouldn't be surprised if they were never changed. Still can't figure out why the sudden change in operating temperature just after fitting a new impeller, especially when the old impeller was missing a few teeth

 

[Henno]

May sound stupid, this is coming from an outboard guy, but did you also service the raw water impeller in the lower unit?

Hi Dingbat. As far as I am aware there is no impeller in my Volvo penta duo prop outdrive, but I stand to be corrected

 

[dingbat]

Hi Dingbat. As far as I am aware there is no impeller in my Volvo penta duo prop outdrive, but I stand to be corrected

Its like I said.. maybe a stupid question.
Only I/O I ever owned was an Alpha

 

[kenny nunez]

If there were some impeller blades missing did you find them? If not then they may be lodged in the elbow that is warmer to the touch. If the power steering cooler is down stream from the raw water pump they may be inside the tube nest. Earlier Volvos had that style but yours may be the straight through type.
If there is a garden hose you can use try back flushing all the hoses.

 

[Scott Danforth]

Check the fitting at the drive where the raw water hose connects to the transom shield

 

[bruceb58]

Just to add also. I noticed today also a marked difference in the temperature of the two risers. The port side remained only warm to touch but the starboard side was much hotter. You would not keep you hand on it for more than a second or two.

Normal for one side to be hotter.

Next time you are in the water testing, put the engine at 100RPM. Remove the hose at the thermostat housing and output the water from that hose into a bucket for exactly 15 seconds. Should get around 2 gallons of water or so.