Coolant passage issues.

Okay guys as some of you know I have been working with a Johnson 4hp 4R70E from 1970. Both of the motors that I have to work with have run hot. Luckily the cylinders are in great working order, even though it is apparent that these motors seem to have issues cooling the bottom cylinder. Here's the proof:

Anyway, in the next picture you can see how the water enters the block. The big hole on the upper right corner flows water to the top of the block, the little bitty hole right next to it, that I am pointing to flows water into the bottom of the block, and on the left about center of the motor there is a water return, that brings the water back out of the motor.


What I propose on doing is drilling the small lower block supply hole, out about 1/16th of an inch for two reasons. A) To permit more water flow to the lower end of the block, and B) to make sure that the little hole does not get clogged with debris, which is what I believe is the main issue with this engineered setup. Do you guys think this is a good idea, or do you think that it will alter the amount of water pressure to the top of the block too much? The difference in sizes is unreal. Has overheating been a problem for anyone with these little motors?

Re: Coolant passage issues.

Anyone got any input?

Re: Coolant passage issues.

Nobody has any input or experiences with these?

Re: Coolant passage issues.

HI sutor623. While I don't think it would hurt anything (famous last words), I've also never heard of anyone else doing it. I would probably try to clean out the existing passages as best as possible using a thick nylon line, like a weed eater string. You can also used compressed air to help clear the passages. I suspect that the overheats were probably due to worn out, or improperly installed water pumps. Check the thermostat too, if your motor has one. The passages leading to and from it can also get clogged over time. I'm curious to know if anyone else has done what your proposing too. Hang in there. I'm sure one of the gurus will be along shortly with a better answer. Good luck!

Re: Coolant passage issues.

kfa4303 said:

HI sutor623. While I don't think it would hurt anything (famous last words), I've also never heard of anyone else doing it. I would probably try to clean out the existing passages as best as possible using a thick nylon line, like a weed eater string. You can also used compressed air to help clear the passages. I suspect that the overheats were probably due to worn out, or improperly installed water pumps. Check the thermostat too, if your motor has one. The passages leading to and from it can also get clogged over time. I'm curious to know if anyone else has done what your proposing too. Hang in there. I'm sure one of the gurus will be along shortly with a better answer. Good luck!

Click to expand...

Thanks for the response. Actually, the reason that these two had overheated is that the little hole in the block for cooling the bottom cylinder was clogged with dirt and corrosion. I just dont want it to happen again.

Re: Coolant passage issues.

here is 4 and 4.5 80' and later block.
its slighty different but you can comper.
if i were you i would take out side panel, clean water chanels under side panel and the rest of water chanels.
let it soak in wd40 or any different solution

Re: Coolant passage issues.

i have drilled holes every where in my block & cylinder head for a radiator conversion iam busy with , & the motor seems to run cooler , i dont know about your motor , try it , the only difference i see is more volume of water getting from A to B

Re: Coolant passage issues.

Dude that is awesome to hear. The issue that I suspected that I may have, is increasing water pressure to the bottom of the block WILL decrease water pressure through the upper part of the block. Question is how much.......

Re: Coolant passage issues.

raczekp1 said:

here is 4 and 4.5 80' and later block.
its slighty different but you can comper.
if i were you i would take out side panel, clean water chanels under side panel and the rest of water chanels.
let it soak in wd40 or any different solution

Click to expand...

Sooooooo, what you are suggesting is that since Johnson didn't make any major changes to the layout of the block they didn't really see a need to?

Re: Coolant passage issues.

Also, raczekp, are you sure that you have the water inlet/outlet holes labeled properly? If you do then I have mine wrong. What you are saying is that water pressure moves UPWARD THROUGH the cylinder water jacket, and the hole at the top of the block is the water outlet hole, that then drains down the block. I am glad that you questioned me because that little hole that was blocked was only the water outlet hole like you said. The water runs out of a hole at the top of the coolant jacket and down the side and out of the motor. So why was my motor running hot then.... Is it okay to soak the whole block in lubricant? Or CLR?

Re: Coolant passage issues.

I don't know if your motor has got pressure relief valves in the system , if it does have i would go ahead & drill as many holes as u wish , the water pressure in the motor depends on the speed the impeller turns , that's when the valve compresses the spring & opens the valve to let the increased water flow out when the impeller turns at high rpm , u should have a by pass system some where in the motor , my personal opinion , drill the hole