Follow-Up on 1968 Evinrude 40 hp Big Twin Overheating/Replace Stat

[supagidget]

I checked the compression last night. I had 105 psi in each cylander on a cold test and water was coming out of the exhaust the last day it overheated. So I think the impeller was properly installed. Could the thermastat be stuck closed preventing water from circulating around the head? I read that you should replace the thermostat and the pressure release valve after an overheat. Just looking at where my thermostat is I can tell it wasn't even checked.

I read some other forum posts about the t-stat and the water cooling system on my motor. It said when the t-stat is closed only a mist will come out of the exhaust but when it is open you will have a greater amount of water in the exhaust.

The motor rarely if ever has more than a mist. I live in Florida and the water temp is currently 88. The motor does seem to cavatate a lot on plane.

It's a mystery but I am going to replace the t-stat tomorrow. Any tips?

As for the garden hose test to see where the water is ciurculating, after dreopping the lower unit where would I connect the hose and where I am looking for water circulating.

I have the original flush kit for the motor, so no muffs here. The guy I take my boat to is a genious with old johnsons and evinrudes. I just don't see how he could say I need a new powerhead without even looking at the motor after the second overheat.

I think he may want to play with his own motors instead of mine...




Ashley

 

[kfa4303]

Re: Follow-Up on 1968 Evinrude 40 hp Big Twin Overheating/Replace Stat

The t-stat could be closed. It's an easy enough fix. However, you shouldn't notice that big of a difference in the amount of exhaust spray mix whether it's open or closed. As for the garden hose test, you'll want to hold the garden hose up to the copper water uptake tube which should've remained in the exhaust housing when you removed the lower unit, then turn it on. You should see water coming out of the exhaust port on the back of the exhaust leg. If water comes through readily, that's good. you probably don't have a blockage. However, if there is poor flow, there could be some debris in the water uptake tube and/or in the water passages around the motor. One more thing, you can't run these old motors on muffs! doing so does not supply the engine with enough water and it may cause the engine to over hear and/or damage the water pump. You have to run these old motors in a test tank (large trash cans work well enough) with water filled up to about an inch or two below the exhaust port. Don't worry if you notice a lot of smoke and oliy residue in the water, that's normal for these old 2 strokes. you'll want to run 50:1 mix on her too. Try these tricks and report back. Good luck.

 

[supagidget]

Re: Follow-Up on 1968 Evinrude 40 hp Big Twin Overheating/Replace Stat

Thank you KFA.

I just took off the t-stat cover and the t-stat was removed. T-stat stuck open is not the problem. Will try to drop lower unit tomorrow to do the garden hose test. Any other suggestions are appreciated. I love all the information on this forum.

 

[supagidget]

Re: Follow-Up on 1968 Evinrude 40 hp Big Twin Overheating/Replace Stat

Garden hose test checked out. Attached hose to one intake tube and the water flowed thru perfectly. Started her up with the lower unit removed and the garden hose attached. Water leaked out of the spark plugs so I took the head off. Cylinders looked good one small score mark and a little carbon build up but otherwise okay. It appears as though the exhaust gasket is leaking. I am going to get the head decked, replace the exhaust garkets, head gasket, head cover gasket, put in new impeller, plate and housing. Let's see if that fixes things.

One question: The drive shaft stayed in the midsection when the lower unit was removed but I don't think it should have. Should I try to get it out?