1975 9.90 evinrude question

[okam]

I have a 1975 9.90 evinrude runs great except for a overheating problem.
Have replaced t-stat, water pump. Did not help, pulled lower unit off 2 times since to check that was not the problem, then changed the t-stat no change. My thoughts are the seal at the top of the water tube to the powerhead. Is there any to test this before I have to pull the powerhead off. thank you for looking

 

[Happy_Jack]

Re: 1975 9.90 evinrude question

A very common problem i have run into on the 9.9 and 15hp motors is that the upper water tube grommet swells up, folds over, and obstructs the water flow from the pump up into the powerhead.
Unfortunately, the powerhead must be removed to access this grommet.
he powerhead removal is not too bad, the worst part is separating it from the leg once all the powerhead bolts (and 3 pan rubber mount bolts) are removed.
That base gasket is tenacious.

The impellers on those are undersized and often delaminate from the inner hub, but you said you already replaced the impeller, and thermostat, so my money is on the upper water tube grommet.
To test easily (although not very scientifically), is to remove the lower unit, take a short piece of hose, slide it on to the lower end of the water tube in the exhaust housing (leg) with a snug fit, and blow into with your mouth, it should be very easy to do, if it is hard to blow into, and you feel resistance, it is almost certainly the upper grommet (or perhaps another obstruction)
Using an air hose for this test is not good, because the high pressure can easily overcome the restriction caused by the grommet, and may give a false indication that the passage is clear.

 

[Rick.]

Re: 1975 9.90 evinrude question

Great advice above. The only thing I would add and it's easier is to make certain you have lots of water in your barrel and the leg is at least covered 1/2 way up. Many times that is the only reason a pump is not pumping properly. Best of luck. Rick.

 

[jmendoza]

Re: 1975 9.90 evinrude question

If you buy the upper tube grommet, buy a power head to exhaust housing gasket as well, and there is also a rectangular exhaust tube seal at the botton of the exhaust tube that usually needs replacement too.

Incidentally, if outboards could walk, they would have legs, but since they cannot, there is no such thing as a leg, but they do have lower units/gear cases, and mid sections. Use of weird cute terms only serves to confuse and should be avoided.

 

[Rick.]

Re: 1975 9.90 evinrude question

"Incidentally, if outboards could walk, they would have legs, but since they cannot, there is no such thing as a leg, but they do have lower units/gear cases, and mid sections. Use of weird cute terms only serves to confuse and should be avoided."Quote:

That is weird. My motors have short legs and long legs and my legs are cute. Rick.

 

[jmendoza]

Re: 1975 9.90 evinrude question

LOL rick, that was a real "leg" slapper!

 

[Happy_Jack]

Re: 1975 9.90 evinrude question

THat is a good point, and you are right, an exhaust housing is just that and NOT a leg. Just some old school (and lazy) terminology I guess.

exhaust legs, gear foot (feet), power heads, lifting eyes, reed fingers, elbow fittings, steering knuckles, wrist pins, shoulder bolts, knee braces, and carb throats will not be used only when absolutely necessary.

 

[jmendoza]

Re: 1975 9.90 evinrude question

It can get better, especially if we get a Newfie or limey: Gudgeon pin, (wrist pin)spanner, (wrench), packing (seal), purchase (grip) offer up (fit, or put in place) and a bunch more arcane terminology, but then again, in th UK they have their own tooks(whitworth).. All toungue and cheek boys, just having fun, hope you all get a laugh

 

[Happy_Jack]

Re: 1975 9.90 evinrude question

Its all good, and I certainly did get a laugh.

THanks,
HJ

 

[bktheking]

Re: 1975 9.90 evinrude question

It can get better, especially if we get a Newfie or limey: Gudgeon pin, (wrist pin)spanner, (wrench), packing (seal), purchase (grip) offer up (fit, or put in place) and a bunch more arcane terminology, but then again, in th UK they have their own tooks(whitworth).. All toungue and cheek boys, just having fun, hope you all get a laugh

Someone has to "kiss the cod".