1973 Johnson 135 hp outboard overheating

[nay9889]

I have a 1973 Johnson 135 hp outboard motor. It has been overheating for a while now. We have replaced the water pump, fixed and flushed the tubes to make sure there is no debris from the old impeller. We have removed the cylinder heads and replaced the gaskets. There is no tell tail to check that the water pump is working correctly. Not really sure where to go from here. Please help!

 

[emdsapmgr]

Just because you replace the impeller does not mean it won't overheat. If the thermostat (vernatherm on that engine) is stuck shut, it won't let the cooling water circulate thru the block and it will overheat. Here is the way to check for normal stat operation: Start the engine cold while running on the muffs. Hold the palm of your hand back by the two exhaust relief ports at the top of the midsection. After about 30-60 seconds, the stat should open. When it does, small water droplets will form on the palm of your hand. That's normal. If you get no droplets, the stat has not opened. If you still have overheat issues, you may need to pull the heads off and check the rubber water diverters by each cylinder liner. Sometimes, crud builds up around them and restricts water flow past them- thru the block. See picture. The left rubber diverter is normal. The right one is out of place and is a problem

 

[nay9889]

Thank you for your reply.
When I put my hand up I didn't get any water droplets. We opened the cylinder heads about a week ago and cleaned up the lining and replaced the gaskets. I don't think water is getting to the T section because after it overheats and we turn it off there is no water residue in those hoses. When researching this specific engine I can't find anything about whether or not this model has a thermostat. We even tried the evinrude/johnson outboard shop manual 48-235 hp 1973-1990.

 

[racerone]

All V-4 motors have a thermostat ( vernatherm ) installed on them at the factory.----You will see it listed with parts on the -----EXHAUST HOUSING GROUP on the parts list

 

[Bosunsmate]

How deep does the lower unit sit in relation to the boats hull?

 

[nay9889]

I have been searching for awhile on where to find to the thermostat (vernatherm) for this motor and can not find anything

 

[sutor623]

As Racer said,

Part number 101 is the Vernatherm, 93 is the thermostat housing cover.

http://shop2.evinrude.com/Index.aspx..._id=0&siteid=1

 

[racerone]

????????----------Not easy to find you say ?--------It is right under the bubble exhaust at the back.-------Not easy for a novice to work on that item.

 

[nay9889]

Sorry I phrased that wrong. I understand that it's inside the exhaust housing and I've seen the break down picture. Was looking for something a little more concrete of how to get into the exhaust housing since we have already removed the 4 bolts at the top of it and can't get the plastic piece to come off. I'm not concerned with our level of experience... fix the boat or we can't get on the water lol.. sorry for the confusion I caused

 

[nay9889]

Got to the vernatherm, was actually incredibly easy.
Put it in a pan of hot water on the stove. it is working just fine. pried open the valve to see if water was coming through while the motor was running, no such luck.

any other ideas to what the issue could be? still not completely sure if the water pump is working correctly. we have flushed the copper tubes and had water coming up and out through the rubber tubes (T housing?)