6 hp Overheating on Top Cylinder Only

[Klink]

I'm bringing back to life for my neighbor's 1968 CD-25A 6 hp Johnson that he got for free. I took off the head and the passages were completely clogged. I scraped all the passages clean. I installed new head gasket and thermostat gasket, new thermostat and seal, and new identical Champion plugs. I changed the impeller and tested the cooling at the heads with an infrared heat gun. It idled OK , and it spit out water well (no pee hole in this model). The heat gun gave me a max of 143 on the bottom cylinder, and 175 on the top cylinder just running it for 3 minutes. I never seen this before, I know the water passages in the cylinder head are spotless, I cleaned them.

OK, back to the drawing board - I removed the new thermostat, and replaced it with one that I removed the hat from it, the top part that opens and closes. I figure this engine runs a t high speed most of the time, so it might help. No change, it still runs 30 degrees hotter at the top cylinder

My Johnson 25hp and 115hp have water passage deflectors, but this 6hp does not show any in the parts diagram or the manual.

I'm stumped, any advice is greatly appreciated.

 

[handsomej0hn]

sorry I can't help you but maybe you can help me. I have a 3hp jw-13 and need piston's and ring's help

 

[Klink]

sorry I can't help you but maybe you can help me. I have a 3hp jw-13 and need piston's and ring's help

Best to start your own thread about your problem. There are people here much more qualified than me to answer your questions. I have never done a piston and ring job.

 

[joereeves]

1968 CD-25A 6 hp Johnson. I took off the head and the passages were completely clogged. I scraped all the passages clean. I installed new head gasket and thermostat gasket, new thermostat and seal, and new identical Champion plugs. I changed the impeller and tested the cooling at the heads with an infrared heat gun. It idled OK , and it spit out water well (no pee hole in this model). The heat gun gave me a max of 143 on the bottom cylinder, and 175 on the top cylinder just running it for 3 minutes. I never seen this before, I know the water passages in the cylinder head are spotless, I cleaned them.

OK, back to the drawing board - I removed the new thermostat, and replaced it with one that I removed the hat from it, the top part that opens and closes. I figure this engine runs a t high speed most of the time, so it might help. No change, it still runs 30 degrees hotter at the top cylinder. My Johnson 25hp and 115hp have water passage deflectors,.

The 6hp does not have water deflectors as you suspect.... Use Champion J6C plugs gaped at .030..... Did you seal the water pump plate to the lower unit and the impeller housing to the plate? (See Below)...... It would be a good idea to remove the exhaust baffle plate cover to clean out those passages also.....

OMC Adhesive is now Bombardier 3M Product #847 and may be listed as Scotchgrip 847, part number 776964.

If running in a barrel or large trash can, be sure that the water is 1" (approximately) above the water pump assembly as it is a non siphoning component (not self priming) and must be submerged except when underway when water is being forced into the pump area.

 

[Klink]

The 6hp does not have water deflectors as you suspect.... Use Champion J6C plugs gaped at .030..... Did you seal the water pump plate to the lower unit and the impeller housing to the plate? (See Below)...... It would be a good idea to remove the exhaust baffle plate cover to clean out those passages also.....

OMC Adhesive is now Bombardier 3M Product #847 and may be listed as Scotchgrip 847, part number 776964.

If running in a barrel or large trash can, be sure that the water is 1" (approximately) above the water pump assembly as it is a non siphoning component (not self priming) and must be submerged except when underway when water is being forced into the pump area.

Here's the water pump system on the engine, it it the updated in 1979 plastic housing system http://www.marineengine.com/parts/j...=6904E&manufacturer=Evinrude&section=Gearcase

The plate has a gasket on top, and it was good, it was already attached with an adhesive, the diagram only shows one gasket #51 on top of the plate, the kit only shows one gasket, however, the description for #51 says two gaskets required. Are you saying that I should also apply adhesive to where it contacts the plastic impeller housing #18? Being as all i'd need to do might be to put some on the plastic housing, can I use Permatex liquid Aviation 3?

 

[Klink]

I got it to cool properly by taking off the lower unit, and hooking up a hose to the water tube up to the engine. I removed the cylinder head and then turned on the water to see what the water flows were and flush out whatever junk I must have missed the first time. Below are pictures of what I conclude are the water flows as far as I can see with it disassembled, any one that can help to correct any wrong assumptions I may have made is most welcomed to chime in.

The problem (I think) was that the water outlet hole at the 7 o'clock mark of the top cyllnder was clogged, and also the thermostat cap was clogged with crud as mark in the attached picture.

After I put everything back together and ran it, you could see a pronounced difference in the amount of water coming out of the exhaust, and the temperature was at 126 and steady (remember I installed an open top thermostat) versus 186 and climbing before. I later put back the new complete thermostat. Will test later today and I expect the temperature should be in the 140's with the new thermostat.

 

[Klink]

I and also the thermostat cap was clogged with crud as mark in the attached picture.

 

[Klink]

This restriction "dam" in the Thermostat Cap caused the crud to get damned up in the water passage as marked. Why is that restriction there? Seems to me that grinding it out might help to avoid it happening again. (see picture)

 

[joereeves]

This restriction "dam" in the Thermostat Cap caused the crud to get damned up in the water passage as marked. Why is that restriction there? Seems to me that grinding it out might help to avoid it happening again. (see picture)
View attachment 14250

No idea... BUT... it's there for a reason... just keep that crud put of there and you'll be fine.

 

[Klink]

No idea... BUT... it's there for a reason... just keep that crud put of there and you'll be fine.

Will do as you suggest. At least it is easy to get to and clean. Thanks Joe.