40 hp overheating

[DCT]

I have a 1960 40 hp johnson, (RDS-22), that is overheating. It seems to have exhaust coming out of the thermostat housing if you remove the cover. I have replaced the water pump, head gasket and exhaust cover gaskets. I have taken a water hose to check flow from thermostat housing to lower unit, water runs through without any problems. While lower unit was off , I tested from lower unit to power head, no restrictions. I could use some advice as to what else to ckeck. Thanks in advance for any help.

 

[Paul Moir]

Re: 40 hp overheating

Exhaust will come up through the thermostat housing if no water is present. The idle exhaust relief and the water outlet share the same passages.<br /><br />A couple ideas - do you have the water pump tubes crossed? Are you testing in sufficient water (the water pump has to be submerged)? Finally, you might want to remove the lower unit and spin the driveshaft in water to see if the pump is actually pumping. If the water intake is blocked it won't pump very well.

 

[DCT]

Re: 40 hp overheating

Thanks for the fast responce. I am running the motor in a barrel, with the cavation plate under water. I will remove the lower unit tomorrow and check the water tubes, I tried to be careful when installing the lower unit, but you never know what can happen. i will try spinning the lower unit in water and see what happens. Thanks again for your help.

 

[CATransplant]

Re: 40 hp overheating

Also, when you have the lower unit down, check to make sure the key for the impeller was properly installed. If it's not, the impeller won't turn, and no water will move.

 

[DCT]

Re: 40 hp overheating

I dropped the lower unit and the water tubes appeared not to be crossed. when I run the lower unit, submerged in water, with a drill to turn the driveshaft, water comes out of the right (starboard) outlet on the pump. Is this correct or is there only supposed to be pressure on one outlet. The manual that I have does not show a diagram of the cooling system water flow. thanks for all of your help.

 

[krb113]

Re: 40 hp overheating

Check your compression and see if a blown head gasket could be suspect. Mine did not pump water with it blown.

 

[R.Johnson]

Re: 40 hp overheating

At the back of the pump intake plate, There is a very thin casting web, see if this is cracked, or spred out. This will give you exhaust gases into the intake water,or a vacuam leak to the pump. This would be on the bottom side of the plate. This will cause the problem you discribe.

 

[DCT]

Re: 40 hp overheating

Update: I installed a new OMC water pump kit. I can get the water pump to pump if I loosen the screws on the thermostat cover. There is no thermostat in the system at this time. It seems as if I have to vent the system to make it pump. As long as the engine is running, the pump operates properly. Let the engine set for awhile, and you have to loosen the thermostat cover again to get water circulation. Any sugestions ???

 

[CATransplant]

Re: 40 hp overheating

Hmm...are you getting any water out of the idle relief hole in the midsection while the engine is running?<br /><br />The reason I ask is that with the thermostat removed, water will circulate without ever returning through the second pipe going to the waterpump, which is there to recirculate water with the thermostat closed. Once the thermostat is open, the water takes another path and leaves the motor through the exhaust system. That includes the idle relief hole in the midsection. That's where you'll see water exiting while running it in a barrel.<br /><br />A couple of other questions:<br /><br />1. Is it possible that you installed the impeller with the vanes bent in the wrong direction? As the driveshaft turns clockwise, the vanes should be curved to drag in the housing. If they're reversed pumping action will be poor, at best.<br /><br />2. When you say that the engine was overheating, we just took your word for it. How did you know it was overheating?

 

[CATransplant]

Re: 40 hp overheating

Also, look at K.B.'s post. If, perchance you have a blown head gasket, that could allow combusion gasses into the water jacket, pressurizing the cooling system and blocking the pumping action. It would also cause overheating.<br /><br />You might be able to detect this with a compression check, but possibly not. In some cases, such a leak only shows up after the engine heats up. It's definitely worth a try. Check compression on both cylinders with the engine cold, and then, again, with it warmed up. If the values are lower when the engine is warm, that's a good sign of a bad head gasket or a slightly warped head. You can resurface the head, if necessary, using fine emery paper on a sheet of glass, rubbing the head surface on it with even pressure and a circular pattern of movement.

 

[DCT]

Re: 40 hp overheating

Thanks for the fast responce. The comperssion on both cylinders is 80 psi cold. The engine starts and runs great, idles smooth. I guessed that as long as the compression is equil, that was ok. I guess that I have to much water in the barrel as the relief hole is under water. The impeller is installed in the proper direction. I assumed that the cooling system was not up to par because there was no water coming out of the exhaust like thre is when you vent the thermostat cover. The exhaust housing gets so hot, after a very short time , that you cannot touch it. By looking at the thermostat housing and cover, it looks like the thermostat deverts exhaust down the right side of the head, is it possiable with out a thermostat in the system, that exhaust pressure could over come the pump pressure ? I ask this because if you vent the thermostat, at the highest point of the cooling syatem, the water comes out of the exhaust as it should.

 

[krb113]

Re: 40 hp overheating

is it possiable with out a thermostat in the system, that exhaust pressure could over come the pump pressure ?<br />Yes, that was the problem I was having. Once I got my head gasket on, it started pumping water.

 

[Blueclaw]

Re: 40 hp overheating

Did you run a hose on the tubes when you had the lower unit dropped? Did the water flow freely to the thermostat housing? Could the tube have a crack in it deverting the water to the mid section?

 

[DCT]

Re: 40 hp overheating

I have double checked everything. If I leave the thermostat cover off and start engine, I have great water flow from the housing. I tighteh the screws and the motor will cool properly. I am going to order all the parts and install a new thermostat. I will post results.