72 Mustang running hot

Sean,
Yes, you can remove the suction side hose from the RWP but keep the end high above the waterline.

Have you checked the condition of the impellers?

Are all you suction side hose connections tight?

You say it runs fine in the driveway and I assume you have it connected to the hose. If so, understand that the water pressure from the hose will mask pump problems.

BTW, what engine is it?

EDIT: I see from a previous post that you have the Chrysler 200.

Sean,
Before the T stat, check the impellers in the RWP. Have you (or maybe the PO) run the engine without water? The rubber impellers are water lubricated so without water it doesn't take long to burn them up.

Yes, I always ran it with the hose hooked up in the driveway. I just pulled the thermostat out to see how it would run wide open and it still started getting hot. Unless the thermostat works opposite a car and opens to relieve water flow to the engine? Instead of opening to provide more water to the engine? Not sure how that would work. Anyways, do I assume I have to take the water pump apart in order to see how it is working?

There are two ports on the top of the water pump. If I turn the pulley by hand the front one pulls in water. The back port does not. Is this correct? I assume the back port should also provide positive pressure and this feeds the top of the water jackets. (Or else it is vacuum and is supposed to pull water up through the water jackets....doesn't sound right) The inlet from the lake is connected to a port on the back directly below the port that does not appear to be working. The hose on the front bottom directly below the top front that is priming goes to the cooler on the transmission. My guess is the top back port should provide positive water flow and that this is the problem?

Sean,
Your engine has a double RWP. Both sides pump cooling water to different engine areas. Chrysler marine engines have a rather complicated cooling system. Take a look at the engine manual in the reference section for the cooling schematic. It's too complicated to explain!

Thanks for all the ideas. The water pump has a secondary inlet with water being pulled through the transmission heat exchanger from the water jackets. Kinda weird. Anyways, this transmission cooler was totally clogged with rust chips. Cleaned it out and I am running much better. Question: What would be an acceptable operating temperature under heavy load? The gauge bumped up above 180 closing in on 200 so I throttled down and it quickly went back to about 120.

Mopars seem to run about 140-160. You also have to remember the gauges may not be functioning properly after all these years.

Pick up a cheap IR temperature gun, It will be very helpful when owning an old boat,

You will want to shoot things like the freeze plugs in the block (thin so you get a good temp reading) and the thermostat housing and intake manifold cross over to get an idea of how hot the water is. You could also pick up a "manual" capillary temperature gauge for testing.

Improperly grounded gauges or low voltage supply to the gauges could over exaggerate temperature rise.

+1 on install fresh impellers before doing much else.

I have not cracked open the water pump, but the impellers look and feel pretty good by inspection from the top. I will open up the water pump at the end of the week and order parts. Latest is a transmission fluid leak. Replaced a hose that I thought was bad but still leaking. Hope it's not a housing or gasket on the unit. I'm gonna quit for the day and take a look tomorrow.

Another idea.. Is the trans fluid leaking when the motor gets too hot? (As the trans heats up as well) Or do you think I have to pull the trans and replace a seal?

Dang, that interior trans seal is going to be a bear of a fix. Any suggestions of how to support the back end of the motor while I pull the trans? Or is engine hoist pretty much the only option?

My new impellers arrived and have been installed in the water pump. The boat now runs at about 150 degrees when I am running it hard. 120 degrees at idle. The transmission starts to slip after a few minutes so now it's time to take that apart and figure out what is going on. Does anyone have any suggestions for a marina that will do a good job of rebuilding a transmission?

It leaks fluid fast into the bell housing. Doesn't slip initially, but slips after a short time due to a serious leak. I will pull trans next week and then look for recommendations from the group.

I guess you just can't wait a week Pete

Give him a chance now   

There are other things that can leak on the front of the pump too