125 H.P. (1258F8C) 1988 overheating

[Justinde]

Hi Guys,

I just replaced ( last week) my water pump. I have a tell tale, and the water is pumping hard. I have also replaced the exhaust plate, and associated gaskets, as there was a build up of sludge in the water jackets. The engine ( power head) had a complete rebuild ( other than the exhaust plate) prior to me buying the boat. It has 150/150/150/145 compression. The power head is free of sludge/grit/gunk. Opened it up, and inspected. Link and Sync done. The engine had a miss yesterday on the water at low revs, that resolved at about 1/2 throttle. When I returned home, the fuel hose was a little frayed, so I replaced the fuel hose. The engine runs strong at home, in a bucket of water, you can rev it, no problem, but under load, and about 3/4 throttle on the water, it overheats. Also, on the water, it doesn't want to idle, but at home, in a bucket, it will idle all day. Its also hard to start on the water, but in a bucket, just hit start.

What am I missing? I'm going to replace the thermostat, but the water flow is just incredible, so is there anything else I need to look at?

Over to the experts!!

If you need any more information just ask!

Cheers

Justin

 

[foodfisher]

RPM's during the problems?

 

[GA_Boater]

Change the fuel filter(s) and rebuild the carbs and fuel pump. I think your motor is is starving for fuel in the upper RPM range and you can melt pistons from running lean. Check compression and spark on all cylinders, too.

Some advice - Don't rev the motor in a bucket or on muffs. It's not good for the motor and eventually your wallet.

 

[Justinde]

Hi Guys,

Half throttle (2500 rpm) when it overheated. Missed under 2000 rpm. When it got going, no miss. Then it overheated.

Thoughts?

 

[jerryjerry05]

You have or have access to a heat gun? make sure it's really getting hot???
The temp sending unit can be too old and breaking down as the motor gets warm?(not likely but possible)


What condition was the pump housing and wear plate?
The old style(you have) is made from pot metal and can work while in really rough shape.
But too much wear on it and the stainless plate can cause it to loose prime at high speeds.(pics???)

Does the pee tube slow down at higher speeds?

The miss at lower rpms: carbs need adjusting?

 

[Justinde]

Hey Jerry,

Thank you.

The waterpump housing and wear plate were OK, but I'll replace them next change ( in 12 months). I used a light 1200 wet/dry sand paper and WD40 to clean the housing. It wasn't badly pitted, I just tidied it up.

The fuel hoses on my return I cut the ends off ( about 1 inch) at the fuel tank and at the filter ( in boat water/fuel seperater) as they were slightly perished. Could this have caused the miss?

The water flows hard at all speeds out of the tell tale. However, it goes from luke warm to ' hey lets make a cup of tea with that' hot.

I never really pushed it hard, the miss goes away at about 1500 rpm, and stays away.

Link and sync done.

Could it be the thermostat?

I'll post photos next week when I take her out again...

Cheers

 

[jerryjerry05]

Sure it could be the thermo.
Pull and inspect and test.
The old impeller, did it come out whole or missing vanes?

The miss: do the starting fluid test.
Start motor and spray SF around the intake side, any change? then it's sucking air.

Remember, ONE tiny burp, cough, backfire can blow the gaskets on the port covers.
That can cause a miss and can burn up a piston.

 

[Justinde]

Hey Jerry,

Hate to be a pain, but how do I do the starter fluid test?

I have starter fluid, just where do I spray it?

Also the previous water pump impeller was not destroyed, it was just warped.

Cheers...

 

[jerryjerry05]

Start the motor, spray SF around the intake side.
Everywhere but in the throat of the carb.
The starter side, spray around the intake manifold base.
The port covers under the coils and packs.

 

[Justinde]

Thanks Jerry,

I just can’t find the problem, so I’m going to replace the ‘88/125 with a new Envinrude G2 115 h.p..

Thanks for your help over the years, I really need to get reliability back, and get on the water!!

I’ll probably put the old girl up for sale....

 

[jerryjerry05]

Good idea.
But buy Mercury or Yam.

 

[racerone]

Usually when you buy a new motor you will say ----" why did I wait so long "-----The E-TEC will be wonderful.----No need for scheduled service for 3 years !-----I think the G2 will start itself when you step in the boat.----Will winterize itself on command too.