1978 9.8 Overheating

[jeff_32]

I have a 1978 Mercury 9.8 that is overheating. I installed a new Mercury water pump kit and still spits water, clearly exhaust is coming out of the tell tale. Compression is good and equal. With lower unit removed I can send water up the tube and it immediately comes out the two exhaust holes before coming out the tell tale. Any ideas?

 

[racerone]

At the top of the water tube there is a plastic washer.-----On severe overheat this washer melts.-----It might block water flow.----Powerhead has to be removed to inspect ----Simple job.----Replacement factory part is better quality ( phenolic ) I think.

 

[jeff_32]

Is it part 10 in this diagram?

 

[racerone]

Correct.

 

[jeff_32]

I have the factory replacement 23-13127 - Spacer.

Is it to be installed as the picture is or the flat side towards the block?

 

[racerone]

Flat side to the block.-----Was the original in bad shape ?

 

[jeff_32]

Flat side to the block.-----Was the original in bad shape ?

I've seen worse. This is a friends "pond" motor. We've spent too much time on it, but it is one of those sentimental things.

 

[racerone]

They are an elegantly simple motor.------What else on it caused you so much grief ?

 

[jeff_32]

They are an elegantly simple motor.------What else on it caused you so much grief ?

Can't get water to flow through it properly. It starts and runs great, but the tell tale spits out water and gets hot. I've hooked up a water hose directly to the water tube, without motor running, and it will not run through the motor and out the tell tale. Most of the water comes right back out from the top of the driveshaft housing.

 

[racerone]

Remove exhaust cover and check for blockage.

 

[tpenfield]

I just went through that on my 7.5 mercury. Plastic gasket melted. It seems like once you have a good overheating of the engine the plastic gasket needs to be replaced.

I also found the gaskets on the exhaust side were perforated, but the major issue was the plastic piece.

 

[jeff_32]

All new gaskets including the spacer that isn't plastic anymore. Still not pumping water right and gets hot fast.

 

[racerone]

Is the water in your test bucket at least 6" above the impeller ?

 

[jeff_32]

Is the water in your test bucket at least 6" above the impeller ?

I have it in a 55 gallon barrel with at least 6" of water above the impeller.

 

[racerone]

Picked up a 79 model 9.8 yesterday.-----Nice looking motor missing a lower unit.----Have a few good lower units here.-----No problem to get it to run properly.