30 HP, '82 Mariner, Cooling System Diagnosis???

[minuteman62-64]

Got an overheating issue. Overheated on the water. Got it to cool down by pulling thermostat). Replaced thermostat and now, running in a barrel, overheats at idle (cylinder head gauge indicates temperature raises steadily to 200+ degrees F) and temperature starts to drop down (to 145 degrees F or so) as soon as I rev it up to 1000-1200 rpm range.

Pulled the LU and will replace impeller. First, made up this pressure tester (see photo) to get an idea of pressure needed to push water through passages. The photo shows the tip that force fits into the outlet of the thermostat housing. I have another tip that clamps onto the water supply tube.

When I squirt water up the water supply tube, thermostat closed, I get good flow from exhaust outlet(s) and tell tale squirts like a fire hose, with the pressure gauge reading 10 psi. Get a weaker, but still decent, flow from tell tale with a reading of about 5 psi.

Pulled the thermostat cover and squirted water through the thermostat housing outlet. At pressures from 5 psi up to 20 psi I get flow from the exhaust outlet(s) and the tell tale roughly comparable to what I get with 5 psi applied at the water supply tube.

So, my understanding is that outboard water pumps put out 3-4 psi at idle and about 16 psi and high rpms. Do the data I have indicate that the cooling passages through the block are reasonably clear?

 

[minuteman62-64]

May have found part of problem. See photo. I have no idea how this happened (or, how it could happen). Anyways, this is what I found when I pulled the pump cartridge - see one impeller vane reversed. Just a quickie analysis indicates close to 20% reduction in pumping capacity

OK, now to put it back together (with a new impeller) and see what happens.

 

[60sboater]

That's a strange one on the reversed vane. Did you turn the shaft the same direction (not back/forth) while installing the impeller. BTW,I'm no expert and have only done that job once...on a '73 9.8 Mercury.

 

[minuteman62-64]

I've done it 3-4 times, and thought I'd routinized the procedure by turning the drive shaft clockwise while pressing the housing down over the impeller. Obviously I did something wrong the last time I did an impeller install.

The good news is that I actually found something wrong that may be (is probably?) the cause of my overheating issue. I'll know when I button everything up and run it again.

 

[minuteman62-64]

Installed new (OEM) impeller plus new base plate. Ran in barrel today. Temperature steady at all rpm ranges and real good flow via tell tale. Put it in water next week, but, I'm pretty sure problem solved.

Doing some forensic analysis. Lost a blade on impeller and replaced it. Had LU off and on a couple of times because of issues with base gasket and new impeller plate. I'm thinking on one of those re-installs I may have turned the drive shaft slightly counter clockwise when installing LU to get the splines to line up. Whatever I did, that old impeller sure took a good set with the reversed blade. It has been siting on my workbench for a week now and still pointing the wrong direction. For those of you that adhere to the idea that if you get the vanes going in the wrong direction they will right themselves when you fire up the motor - well, maybe not always

I remember on my last run, when I had the overheating problem, my buddy took the boat to the dock. He said he shut it down at the dock because he thought it might be getting too hot. I didn't think much of it at the time since the temperature was good running out of the launch area. But, the reversed impeller blade could have started the overheating while we were idling around the area we were fishing. Maybe pulling the thermostat helped - not because the thermostat was bad but because removing it allowed more cooling water flow, compensating for the reversed impeller blade. I did test the old thermostat (after buying a new one) and it tested good.

Oh well. Live and learn. Hopefully this issue resolved. Lets see what the next one is (the joys of a 30+ year old motor ).

 

[minuteman62-64]

Did a 2 hr. run in San Diego Bay yesterday. Temperature holds steady at various throttle settings, although seems to be about 10 degrees F higher than on previous runs. Hard to tell with Bay water temperature in mid-70's - maybe the relatively high ambient temperature is cause.

Anyways, good flow from tell tale. Good flow from exhaust. Exhaust flow warm to touch, tell tale flow cold, which is the way it usually has been. I'll keep monitoring, but, hopefully its a fix.

 

[minuteman62-64]

May have found part of problem. See photo. I have no idea how this happened (or, how it could happen). Anyways, this is what I found when I pulled the pump cartridge - see one impeller vane reversed. Just a quickie analysis indicates close to 20% reduction in pumping capacity

OK, now to put it back together (with a new impeller) and see what happens.

​Kind of a delayed reaction, but, I think I figured out what happened (while doing a new impeller replacement). To disconnect the shift shaft the LU has to be in reverse so I can reach the coupling. I think I had it in reverse when putting the LU back in place - turned the prop shaft clockwise to line up the splines, which of course turned the drive shaft counterclockwise. Another lesson learned.

For you guys that adhere to the idea that the impeller blades will just flop into correct position as soon as the engine starts cranking - take a look at the photo. Not always

 

[GA_Boater]

Did you grease the impeller during the install?

 

[minuteman62-64]

Did you grease the impeller during the install?

.

​Yep. Always do that - probably to the extreme.