58 evinrude 7.5 cooling problem

[twocyclemania]

My 58 Evinrude 7.5 seemed to be running a bit hot so I decided to replace the pump/impeller. When I opened it I found the pump looked good. It's a plastic pump body that had apparently been a replacement. I opted for just a new impeller (pump expensive). Put a new rubber grommet on the water tube of the pump body just for safety. Put it in the test barrel and it seemed to be producing little water out the exhaust. Motor heated up to where if you put drops on the head they sizzled off (too hot) after a few minutes. I popped the power head and broke it down. The chambers looked dry; like it wasn't getting water. I checked to see if the key at the impeller had broken (my first thought) but it was okay. It seems like it's just not pumping water though it should. I didn't replace the grommet that's up in the leg though it looks good and I doubt it's the problem. Motor has had very little use and zero corrosion (fresh water). Seems pretty simple but I can't figure why it's not getting a nice cooling flow after the new impeller. Any ideas? thanks!

 

[Scott Danforth]

is the water in the bucket well over the impeller?

 

[racerone]

The water in your test bucket MUST be 8" above the impeller.

 

[twocyclemania]

It's well over 8 inches. It's close to the coolant exhaust. I was worried that I had too much water in the barrel (rain) and wouldn't be able to feel the coolant water flow.

 

[racerone]

Did you put the copper tube into the upper grommet first.------And then install the lower unit ?

 

[twocyclemania]

Copper tube never came out of the upper grommet. I was going to replace it but it appears intact and the rubber looks good. A tight fit. No signs of blockage or leakage at that point.

 

[F_R]

Look up inside the water tube. Does it have a restrictor up in there? Those restrictors, (when equipped) get partially plugged with trash. Here in Florida, I used to enlarge the hole with a drill. I can't say what to think about that "Up North" and cold water.

 

[Crosbyman]

when did this issue start recently, suddenly, after repair work . ???

if you remove the PH (easy) you may be able to spin the drive shaft clockwise and see if water is coming up the water tube. it should !
IF not then you have the issue narrowed to the lower half of the motor

if OK ... well check the PH for obstructions

 

[racerone]

Part # of the new gasket you used between block and exhaust housing ?

 

[twocyclemania]

Part # 0304314

 

[twocyclemania]

I think Crosbyman has a good idea for a starter. I'll try that will an electric drill on the driveshaft if I can't figure anything else out. I thank everyone for the suggestions and interest and help.

 

[racerone]

So it has the updated kit as found on a 79 model 6 HP ?----Hard / nearly impossible to assemble one of those pumps so it would not work.----Intake screen behind propeller clear.

 

[Sea Rider]

If after spinning the drive shaft as suggested by Crosbyman water doesn't flow upward with a nice flow check the hidden vertical water passage located under the water pump's base which extends to the lower leg's cavity. Pic is just a reference....

Being a 63 year oldie expect to find some passage reduction which needs to be impeccable clean for the water pump to suck and pump a much better amount of water towards the powerhead.

If still with overheating issues, remove the thermostat if counts with one, bolt lid back on and connect a garden hose with proper fittings to the middle leg's lower water pick up tube, flush it for as long as you want.

If the issue continues and there's no anode inside the powerhead that might been clogged over time, that motor has already accumulated large quantities of scale inside all their narrowed cooling water passages which needs to be taken care flushing a descaler fluid which should be the fastest way to have the motor in full operation shortly after...

Happy Boating​

 

[twocyclemania]

I took Sea Rider's advice. Opened up the plate below the water pump (didn't do that before) and found some gunk but not what I would consider to block any flow. Cleaned it out completely including the underside of the pump plate. Checked passages in the leg with wire and pouring water. They are very clear to begin with but tested them anyway. Hooked the shaft up to a drill with the lower unit submerged. No flow out the top at all. I re-opened the lower unit thinking maybe the key at the impeller is sheared at the base and I missed it. The key was fine. This whole thing has me puzzled. All in all this motor was used very little and in fresh water (it was a duck hunters motor). I'm no genius but I've worked on many other motors and never had a problem like this with a cooling system. Thanks again for all the help.

 

[Crosbyman]

check the new pump housing it should have air passages to prevent air locks etc... or something similar clear all passages

 

[racerone]

I believe this motor has the 79 Model 6 HP water pump kit installed.----Where is the gasket installed ?

 

[Crosbyman]

One service bulletin from Evinrude # M168 says to remove the side plate when bucket testing &
while removed .....also recheck for obstructions (crud) in the cavity and screen on the water pick-up

when reinstalling the plate ensure opennings are facing FORWARD !!

retest with a drill with gearcase only with the water pump section fully submerged

check the new impeller in case the rubber parts do not hold on the brass core

 

[twocyclemania]

Racerone: You mention a gasket (at base of water pump?) Uh Oh: There was one there (kinda beat) but not in the diagrams I've seen of the motor. I thought someone added it by mistake. I'm now picturing that it does need one and (cleaned up the remnants) I didn't add one. ????????

 

[twocyclemania]

Crosbyman: I though what you said about a defective / spin off the body impeller. That was going to be my next move.

 

[racerone]

Answer this question,-----Does your motor have the 79 model 6 HP pump installed , yes , no or no idea ?-----There is a special gasket ( 79 style pump ) and it goes between the pump housing and the plate !-----Time to stop and regroup I say.-----Fixing these simple pumps takes about 10 minutes !