Mercury Outboards 75 and 9.8 overheating problems

[Mark A. Klein]

Hello, I am having trouble with both my 75 and 110 Mercury Outboards. My 7.5 hp use to run just fine - 2 years ago. Last year the water tell / tell port was barely spitting water. This year it started pumping water then quit. I tried to baby it back to the dock stopping often and trying to keep it splashed with cool water. I actually had never used the 110 - 9.8 hp. I have replaced the impellers on both motors. Now the 9.8 barely spits water and it is HOT!. My 7.5 does not spit at all, but blows only hot exhaust gas out of the tell / tell port. I took the side cover off the 7.5 and the gasket both looked good. I have had them both apart several (many ) times. At one point I did have the grommet in the water pump it self folded over a bit. I straighten the copper tube thinking that it would better reseat itself. That may be causing too much pressure on the seals?
At any rate it has been very frustrating and I would like to know what I need to do to get these good little motors back going.... I have not had the head off yet. What gaskets should I buy? Should I check the head for warp? Who else has had this problem?
Thanks for your help!
Mark
Feel free to call or email with help also.
515 681-1759 or mklein@iowatelecom.net

 

[oldman570]

Re: Mercury Outboards 75 and 9.8 overheating problems

You will need to drop the LU again and hook a water hose to the water pipe to the motor and see if you get water to flow thru the motors ,they do not need to be running,first. If water flows then the pump is the trouble. You will need to replace the cup as it could be worn bad enought to not seal on the new impeller. Older 110's used two diffrent size impellers as the DS is diffrent sizes where the impeller fits. There is no head on the motors as the cylenders and head are cast with the block half in one piece. What you think is the head is a water jacket and is probbly fine as long as there is no water leak around the plugs or edges. This goes for both motors. running a piece of weed eater string up the tell tail will disloge any small blockage in them, as bugs love to make nest in them. When running the motors in a barrel the water in the barrel has to be atleast 6" above the cavation plate inorder for the pump to prime itself, if not you vary well might not get any water thru the motor.
Oldman570

 

[Mark A. Klein]

Re: Mercury Outboards 75 and 9.8 overheating problems

Sorry, my last replie did not go through. So far I have made sure it was in deep water in a 55 gallon barrell. I can blow through the copper pipe both directions. I have straightened the copper pipe in order to help get more compression seal on the seals, wich only resulted in collaping the seal in the top of the water pump. The SS wear plates look good with no signs of grooving. I do get hot exhaust gasses through the tell/tale weep hole. I do have the proper sized impeller and the key is in place to drive it. Where is the exhaust gas coming from? What do I try next? Thanks! Mark

 

[oldman570]

Re: Mercury Outboards 75 and 9.8 overheating problems

There is a exhaust water jacket plate on the side of the motor with another thin plate under it that could have a crack in it from being run with the impeller bad and no water as should be. There is also a gasket between the powerhead and midsection that can be bad. If a compression test has not been done, do it first to see if the motor is worth fixing. Small motors as those are used alot for winter sports and they will fresse up if left in the water and crack the block witch could be causing your trouble.
Oldman570