1966 Johnson 40HP outboard - cooling

[Classic Ski-Boat]

Hi, I have a 1966 Johnson 40HP outboard (RD-28B Model) and when underway at about 5-7 knots, water comes out (spits) out of the tell-tale outlet ... but when I increase the speed and revs there is no water coming out. What is the problem and how to fix it? Thank you.

 

[lindy46]

Re: 1966 Johnson 40HP outboard - cooling

Should spit more water at higher speeds. Check intake screen by prop and make sure it is not plugged. Could be the impeller - how long since that's been replaced? Also check the thermostat and make sure it's working properly. Should open between 140 and 160 degrees F.

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP outboard - cooling

Should spit more water at higher speeds. Check intake screen by prop and make sure it is not plugged. Could be the impeller - how long since that's been replaced? Also check the thermostat and make sure it's working properly. Should open between 140 and 160 degrees F.

Hi and thanks Lindy. The intake screen looks clean. The impeller was replaced 2 years ago. I am new to boat engines but othewise I am OK technically. Do I need to take the thermostat out? Is it on top of the heads/cylinders under the cap with 3 bolts? Will I be able to replace the impeller by myself? Thanks a lot.

 

[lindy46]

Re: 1966 Johnson 40HP outboard - cooling

Yup - thermostat is under the cap with 3 bolts. You can test it by suspending it in a pan of water on the stove. Heat the water and check with a thermometer and see where it begins to open. Don't let the t-stat sit on the bottom of the pan. I use a fine wire to suspend it. With the t-stat out, check the water passages and see if they are gunked up. To replace the impeller, you need to drop the lower unit. You'll see the 6 bolts holding it on, but there is another large bolt at the back of the motor which is hidden. You have to remove the rear exhaust housing to get to that bolt. It goes through from the top. The exhaust housing is held on by a bunch of Phillips head bolts. If it has a manual shift, there is a small oval plate on the side of the leg which you must remove to get to the shift rod coupler. Remove the bottom bolt from the coupler to free the lower shift rod. If it is electric shift, there are two wires which must be disconnected under the exhaust housing. Once the shift rod or wires are disconnected the lower unit should drop down. The impeller is under the water pump housing on top of the lower unit.

 

[coolguy147]

Re: 1966 Johnson 40HP outboard - cooling

thats weird? i have the same problem with my 1958 35hp model. it never over heats even at high speed. i noticed that it does not really pump water out the back as much as it does when at low speed. my impeller is almost a year old. new t-stat too. again it never overheats.

 

[bktheking]

Re: 1966 Johnson 40HP outboard - cooling

F_R has explained how the system works when the question comes up, see the following:

http://forums.iboats.com/showthread.php?t=353846&highlight=40hp+water+pump

 

[a70eliminator]

Re: 1966 Johnson 40HP outboard - cooling

I wasn't going to say anything but.. tell tale on a '66' ?

 

[bktheking]

Re: 1966 Johnson 40HP outboard - cooling

I wasn't going to say anything but.. tell tale on a '66' ?

Ya I know, there isn't one, but then again Duane Johnson is the Tooth Fairy

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP outboard - cooling

Yup - thermostat is under the cap with 3 bolts. You can test it by suspending it in a pan of water on the stove. Heat the water and check with a thermometer and see where it begins to open. Don't let the t-stat sit on the bottom of the pan. I use a fine wire to suspend it. With the t-stat out, check the water passages and see if they are gunked up. To replace the impeller, you need to drop the lower unit. You'll see the 6 bolts holding it on, but there is another large bolt at the back of the motor which is hidden. You have to remove the rear exhaust housing to get to that bolt. It goes through from the top. The exhaust housing is held on by a bunch of Phillips head bolts. If it has a manual shift, there is a small oval plate on the side of the leg which you must remove to get to the shift rod coupler. Remove the bottom bolt from the coupler to free the lower shift rod. If it is electric shift, there are two wires which must be disconnected under the exhaust housing. Once the shift rod or wires are disconnected the lower unit should drop down. The impeller is under the water pump housing on top of the lower unit.

Thanks a lot Lindy

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP outboard - cooling

Thank you guys for all your comments.

Coolguy ... do you keep running your engine without any water coming out at high speed? I am scared to do that - I do not have a temperature gauge.

And yes, I guess it is not a real tell-tale on the 1966 engine but I think it works as one.

So, if I'll check and possibly change the impeller, what shall I lubricate the impeller with (I read that it should be slightly lubricated before the first use - but nobody mentions what to lubricate it with). Can I use the same marine lubricant I use on wheelbearings on the trailer? When I'll put the water-pump back together do I need to use any sealant on surfaces or bolts?

Thank you.

 

[EN2]

Re: 1966 Johnson 40HP outboard - cooling

For lubing the impellor, I have used triple guard grease. two stroke engine oil,vaseline, dish soap works good too.

 

[1946Zephyr]

Re: 1966 Johnson 40HP outboard - cooling

Yea, if you put a light coat of oil on the drive shaft spline where the o-ring is and in the grommet where the water tube is, things will go back together a lot easier too.

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP outboard - cooling

Thank you.

Another question ... I am taking the lower unit off right now - I expect the lower unit will come out with the drive-shaft (correct?) ... should the whole thing just fall out? I am pulling it out but can't get it out ... how much pressure do I need to apply to get the lower unit with the drive-shaft out??? Thanks.

 

[bktheking]

Re: 1966 Johnson 40HP outboard - cooling

Thank you.

Another question ... I am taking the lower unit off right now - I expect the lower unit will come out with the drive-shaft (correct?) ... should the whole thing just fall out? I am pulling it out but can't get it out ... how much pressure do I need to apply to get the lower unit with the drive-shaft out??? Thanks.

Couple things, shift linkage undone from under the 2 covers on the side of the exhaust housing? You remove one then the other, shift into forward and remove the bottom bolt.

Did you remove the back cover that covers the entire leg? Pretty sure on this model there is a hidden bolt under the cover.

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP outboard - cooling

Couple things, shift linkage undone from under the 2 covers on the side of the exhaust housing? You remove one then the other, shift into forward and remove the bottom bolt.

Did you remove the back cover that covers the entire leg? Pretty sure on this model there is a hidden bolt under the cover.

Hi and thanks. I am working on this as we speak ... yes, hidden bolt undone and bottom bolt undone (loosened, just hanging there) and still no easy movement out ... so should I apply any pressure? Thanks again

 

[1946Zephyr]

Re: 1966 Johnson 40HP outboard - cooling

I would just grab the anti-cavitation plate with both hands and wiggle the lower unit back and forth as you apply a little bit of downward pressure. This should work out fine without harming anything. It's usually the shift rod coupler and o-ring on the drive shaft top that makes it hard to get off. Water tube can help make it hard too. And yes, the 66 model does have the super quiet shrouding and the rear half has to come off. Once you remove that, then you'll see the obround plate that covers the shift rod coupler.

 

[bktheking]

Re: 1966 Johnson 40HP outboard - cooling

Hi and thanks. I am working on this as we speak ... yes, hidden bolt undone and bottom bolt undone (loosened, just hanging there) and still no easy movement out ... so should I apply any pressure? Thanks again

As long as all the bolts are undone and the shift linkage disconnected it should drop. Try tapping on the a/v plate with a mallet and a block of wood but don't go crazy as it will split the aluminum.

 

[lindy46]

Re: 1966 Johnson 40HP outboard - cooling

Hi and thanks. I am working on this as we speak ... yes, hidden bolt undone and bottom bolt undone (loosened, just hanging there) and still no easy movement out ... so should I apply any pressure? Thanks again

The bottom bolt on the shift rod coupler MUST be completely removed to disconnect the shift rod.

 

[Classic Ski-Boat]

Re: 1966 Johnson 40HP outboard - cooling

Hello everyone and thank you again for your support.

I managed to get the lower unit off - after applying more pressure, some serious wiggling and removing the gear-connection bolt completely, it came off.

The impeller looks good ... hmmm ... what to do now???

A couple of comments:

1. I was surprised to see that the water circulates even under the stainless-steel plate (under the water pump lid) ... is this correct?
2. The oil in the lower unit looks a little 'milky' ... it was changed just 2 months ago! Should I be worried or is this pretty normal?
3. Should I try to flush somehow (how) the whole water cooling system (going up to powerhead), considering the fact that the lower unit is off? If yes, should I take the thermostat out?
4. Is it possible that this engine will never spit the water out (out of the top outlet) ... as is in the case of Coolguy's 1958 35HP engine?

Thank you.

 

[bktheking]

Re: 1966 Johnson 40HP outboard - cooling

1. I was surprised to see that the water circulates even under the stainless-steel plate (under the water pump lid) ... is this correct?
2. The oil in the lower unit looks a little 'milky' ... it was changed just 2 months ago! Should I be worried or is this pretty normal?
3. Should I try to flush somehow (how) the whole water cooling system (going up to powerhead), considering the fact that the lower unit is off? If yes, should I take the thermostat out?
4. Is it possible that this engine will never spit the water out (out of the top outlet) ... as is in the case of Coolguy's 1958 35HP engine?

Thank you.

1. Yes that's how they work and as far as water pump is concerned if it hasn't been replaced in a couple of years and you don't know when it was last replaced you should replace it.

2. Oil shouldn't be milky and if it is water is getting in from the drain plugs or one of the various seals in the lower unit.

3. You could try flushing it but it may not have a blockage, getting a new pump installed will tell for sure, just an added step.

4. It should by design and if it isn't it shold, plain and simple. Do the pump and flush then retest, too many unknowns.