Engine overheated, really frustrated.

Your brand new impeller may be defective even though it looks normal. The squealing noise may be the giveaway. Check it using the test in the first post in this thread:

https://forum.moomba.com/showthread....the-week-month

I checked the impeller and didn't notice it free spinning when holding pliers inside the channel.

I believe this is the water pump I need, just to confirm

https://www.bakesonline.com/detail.aspx?ID=774

Also, how worried should I be about having caused significant mechanical damage? I'm getting a general feeling that I shouldn't worry too much about it, just change thermostat and water pump then go ahead and test and check for overheating. I was considering doing a compression test on all cylinders and changing oil before I start again, but it really doesn't seem necessary from the replies?

On a side note should I buy the OEM 40 dollar thermostat or go cheap and get the sierra replacement?

Thermostats are cheap, no need to spend 40 .

Compression test is the best way to check for blown head gasket, also water in oil.

The only other thing to possible check is the belt. If the belt is loose it may be slipping on the water pump and therefor not spinning it. That will make a squealing noise as well.

So like I said I'm a newb but I learned today that I have two water pumps, the Johnson raw water pump and the main circ pump that was linked earlier in this thread. I have a new thermostat and main circ pump on order and plan to do a compression test. I will keep you posted.

Thanks for everyone's help thus far, this forum is a great resource.

If you happen to have another impeller kicking around you may want to try comparing the two.. You may find this one is longer, or deeper than the other. I found one like this , and it caused a squeeling noise from basically rubbing on the front cover withe the brass screws..Not sure what caused this in mine as it was a impeller i had used the previous season and packed in Vaseline... As per Moomba instructions.. I do not do that anymore.. Maybe this will help.

Wasn't there and issue with hoses on the 07 models that would fail overtime. I remember the person I sold my XLV to in 2010 having an issue after a few weeks after I sold it to him.
Might check the hoses underload and see if they are collapsing.

Start with some basics. Did you check the oil for signs of water. The caps may have a milky coating on them. That would be a key sign for head gasket during an over heat. Pull the temp sending unit and check it with a volt meter to see if it has failed. Check online for the resistance for your model. A failed sensor send a signal to the ECM and yes it will/can go into limp mode.

Both of those things are basically free (if you have the tools). Compression test if you have or can "rent" the tool. Then put it on a fake a lake and see what happens. After that, think about replacing parts and spending money.

Could you explain in a little more detail how to check the temp sending unit with a voltmeter?

Just an update, ran a compression today this AM and all cylinders are within 123-132 which makes me feel a lot better! Also plugs looked good.