Still really confused about overheating

[AJ168]

After changing the water pump in my 1970 Evinrude 4 hp, the engine began to overheat when run. A good spray of water comes from the exhaust, but it comes out cold, while the powerhead gets very hot, too hot to touch. My first thought was that maybe the fuel pump didn't go into the water tube running through the lower unit. But it was and while I had it apart I also rechecked the water pump, and hooked the tube up to my garden hose, water came out from where it should in the powerhead inside the lower unit. But it still overheats. The first thing that I checked was a thermostat but found none on this motor. Could there be a blockage in the head, and the water could be flowing into some sort of relief?

 

[krb113]

Re: Still really confused about overheating

Check your compression. If you have a blown head gasket, the pump is working but can't get enough pressure up to the power head.

 

[Solittle]

Re: Still really confused about overheating

See if you can borrow or buy one of those electronic temperature guns to verify that it is overheating. You could also use temperature sticks.

 

[AJ168]

Re: Still really confused about overheating

I figure that if the cylinder head burns my hand then it's running too hot. I will do a compression test and get back with the results. I don't think that the engine would run right without good compression, it runs perfectly except for this overheating problem.

 

[AJ168]

Re: Still really confused about overheating

I had an idea that it could be the water tube running through the lower unit that's leaking. Has this ever happened before to anyone?

 

[itstippy]

Re: Still really confused about overheating

I believe you are right. The upper end of the water tube is attached to the lower motor cover with a compression sleeve and nut. I suspect that the top of your water tube is cracked at its fitting, and the water is merrily taking the path of least resistance: up the tube, out the crack, into the exhaust tower proper. It's bypassing the powerhead cooling passages entirely.

 

[Al Mottola]

Re: Still really confused about overheating

Hi, AJ168's dad here. I believe that this or a split in the tube itself is the most likely cause of the over heating condition. Does anyone have an exploded view of the water tube with the compression sleeve and nut? It does NOT show it in the shop manual. In liew of that, Do I need to remove the power head from the center section to get to this sleeve and nut?

 

[Chinewalker]

Re: Still really confused about overheating

Yep, just pull the four bolts that hold the powerhead/lower pan all in place. The water tube and compression nut part will be right there. Nothing is going to jump out at you by pulling the powerhead, although it helps reassembly if the lower unit is already off.<br /><br />- Scott

 

[Chinewalker]

Re: Still really confused about overheating

FYI - the cylinder heads on those motors are not very well cooled and will get quite hot to the touch. Water only circulates along the outer edge of the head. Also, the exhaust cover is only cooled on one edge, so it too will get quite cool. The most likely area of possible blockage as along the cooling water path that goes up and over the top of the motor block. It narrows and can be blocked by misc. waterborne debris quite easily...<br /><br />- Scott

 

[Al Mottola]

Re: Still really confused about overheating

Thanks Scott. <br /><br />OK, I will pull the power head, and if I have to remove the lower unit, so be it. <br /><br />I am assuming that once the power head is off, I can use the garden hose and force water through the cooling jacket. This should remove any blockage. (Unless it is some kind of calcium deposits.)