Impeller issue

[Surfdad]

Ok guys and gals...I know something is wrong, but I don't know what. I have an '03 23V and over the 4+ years I've owned it I've had to replace the impeller twice a year. Literally this latest replacement is number 8.

Took the boat out today for the first time this season, fresh impeller and housing. Boat is idling in the water and the the temperature gauge is pinned at 220 after 5 minutes.

What could be causing the impeller to self-destruct twice a year and then today, with fresh everything to overheat in the first 5 minutes of operation?

[Surfdad]

Shoot - forgot the engine details - Merc Black Scorpion.

[lee]

When you replace the impeller, do you pull out all of the parts to the old impeller? If old parts are left in the lines they will destroy the new impeller.

[Surfdad]

Yeah, I've changed it once and the rest of the times it's been either at the dealership or another local mechanic...I know that I accounted for every piece, I'm presuming the dealership used due care.

[FIC]

Have you inspected the complete suction side from pump to through hull to make sure there are no obstructions.

[Surfdad]

Not on this most recent overheating, but I did over a year ago. Took the hoses off at the V-Drive and again at the thermostat block and used a garden hose to flush down through the thru-hull. Water flow was fine and nothing was dislodged. Visually, there didn't seem to be any evidence of blockage. Is there anything I am doing wrong in trying to isolate the cause?

[Coach]

Not sure about the impeller issue, but did you check your thermostat? For it to pin like that tells me the thermostat is not opening and the water is recycling in the block. You might replace the thermostat and see if that make a difference with the temp issue.

[Surfdad]

Yeah Coach, I think that you could be right on this current incident. I didn't replace the thermostat this last overhaul and NORMALLY when the impeller goes out it freezes up and we didn't have that this time.

[Moki]

You may want to try the "run dry" impellers that are more durable.

http://www.defender.com/product.jsp?...3460&id=140952

Also, is your impeller housing all scratched up? Mine is starting to become that way and I am probably going to replace it next impeller change.

On my Four Winns, I ran it for 10 years on the same impeller

[Surfdad]

I was unaware of the "run dry" version of the impeller, I think I may switch to that. Any drawbacks?

Coach was right - this incident was a thermostat issue. I took it out and tested it by placing in a pot water without touching the sides and heating the water - the water temp got up over 200 and it still hadn't opened.

Moki on the impeller housing it looked melted! The last time I had the impeller changed, the now defunct dealership, did the repair...it seems to me they didn't bother to change the housing. I'm wondering if that has been the problem for a much longer period of time that I was aware?

[rpaxton]

He guys! I have a 2000 22i that is overheating. I have two questions:

1. The thermostat has a large plastic insert holding the thermostat in the housing. Do I need to try to salvage this piece or does this get replaced with a new thermostat?

2. Did anyone try these new run dry impellers, and do they work? How do I determine what size to order??

Thanks,

Rodger

[R&T Babich]

Rodger - I talked to a guy at Mercruiser and he said that plastic piece is a shield, but was not sure what it really did. I think it's a GM thing. It can be reused. Our 2000 350 Mag MPI has a Mercruiser raw water pump, 807151A, for which Globe does not make a run-dry impeller. The size should be exactly the same as your old impeller. A Globe impeller, if they made one for mine, I was told would look just like original, but with the blueish rubber.
For your overheating issue here's some possible problems:
Most likely:
1. Raw water impeller not working (it's the part that's moving all the time). The vanes may be missing pieces, the housing may be scored and not sealing, or the bearing is tight causing the belt to slip.
2. Something got thru the thru-hull grate and is clogging the line. Ours had chunks of cardboard in the V-drive cooler chamber. Remove the pipe fittings and look inside. Other debris may have gotten thru the raw water pump and lodged in a cooler. A raw water strainer would prevent this.
3. Thermostat is not opening. Remove and test in hot water.
Not so likely:
1. Engine cooling pump not working. Pump vanes missing or shaft broken. Bearing is tight and belt is slipping.
2. Sensor or gauge not working properly. Test with another gauge/sensor.
3. Hose between raw water pickup and impeller was replaced with a cheap radiator hose and is collapsing from the suction.
4. Engine could be running really lean.

Roger

[spharis]

The run drys work great.

[rpaxton]

Roger,

I know for sure that it is not a gauge issue. When I was being pulled, right before the temperature alarm went off, I could smell the engine was running very rich. The inlet hose from the raw water pickup is factory, it has the wire coil in it to prevent it from collapsing. I still need to pull it off the hull to check for debris.

Where can I get a raw water strainer, and where in the system does it get installed? My guess would be between the hull and impeller?

Thanks for the info!

Rodger

[bk3104]

Here is the link to pictures of my strainer installation on a 24VE. Strainer is installed between the water intake and the trans cooler which on my boat is the first point of clogging.

http://www.tigeowners.com/forum/showthread.php?t=3911