1988 70 HP Johnson Cooling System Modification (+ Additional Work)

[Faztbullet]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

Reason for the cooling system modification?

One of the main reasons was due to block design as 1988-1993 60hp and 1984-1992 had a bridged ported exhaust and if block got hot from aerated water( water would turn to steam inside block) the cylinders ran hotter causing the "bridge" to expand and scuff exhaust side of piston. The tattle tell would still show impeller working and you would get no alarm horn. The "mods" address this problem.....

 

[NoEcm]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

Here is a seller added description of the kit that I bought:



And in looking at the factory parts diagrams, 1996 was the first instance I could find where the Water Pump Indicator was officially moved to the top of the crankcase:



And a diagram showing the plug and part number used on the exhaust cover:

 

[NoEcm]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

One of the main reasons was due to block design as 1988-1993 60hp and 1984-1992 had a bridged ported exhaust and if block got hot from aerated water( water would turn to steam inside block) the cylinders ran hotter causing the "bridge" to expand and scuff exhaust side of piston. The tattle tell would still show impeller working and you would get no alarm horn. The "mods" address this problem.....

Excellent explanation and thanks!!!

 

[NoEcm]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

Masked up and painted. When fully dry, the finish will be a satin black:


Fully assembled with the new tell tale hose in place. Wanted to make sure the hose was routed so that all the water would drain out of it when in storage:


And the new tell tale nipple:

 

[NoEcm]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

Exhaust cover installed with the water pressure elbow for the gauge pointed forward:



Figured this would be the end of this thread as a simple water pump R&R has been covered many times over in this forum and there would be no point in covering it again.


However:


The @%^% impeller was frozen to the drive shaft. I used a screwdriver to try and wedge it up with no success.

 

[NoEcm]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

I used a box knife to cut the rubber vanes off the collar:


I found the sweet spot where the "key" was installed and I used a rotarty tool to cut a slot in the collar:


Next, I used a screwdriver and with a little twist, the collar split relieving the tension on the driveshaft:


And the collar slid right off:

 

[NoEcm]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

Old parts on the left and new parts on the right:


The impellers are the same as I did a water pump R&R a few years back.
However, the stainless steel liner in the new kit is one piece and the old one was 2 pieces.

All cleaned up and ready for the new water pump:


Water pump installed and gearcase re-installed. Time for a little sanding to prep for painting:

 

[boobie]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

Note the change in the impeller hsg cup. They went from two piece to one. This also helped with the water flow.

 

[WernerF]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

Yes, and the water inlet in the bottom plate has changed as well.
Thanks for the photos.

 

[NoEcm]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

A follow-up, and my final posting to this thread.

Yesterday was the first time I had the outboard out on the water since my rebuild and here are some of my observations after about 1 hour of run time:

Water pressure with the new impeller and modifications:
12psi @ idle
20psi @ WOT
(These are the same pressures I got when I first purchased the outboard in 1988).

Since the tell-tale restrictor was removed as part of the cooling system modification (post #11 of this thread) the new tell-tale water stream seemed to have less pressure but a whole lot more volume.

Also, when starting the outboard the tell-tale stream seems to have some water bubbles in it for the first few seconds until the air in the upper cooling system gets purged. As noted in OMC Service Bulletin 2276 (Post #1 of this thread) this was the whole purpose of this modification:

?Problem: An engine can be damaged by overheating when air becomes trapped in the upper half of the cooling system.?

?Solution: Relocating the water pump indicator tee to the top of the cylinder block ensures air can be vented from the cooling system and an adequate water level in the cooling system can be maintained at idle.?

I would say that the modifications were a success based on my observations and I wouldn?t hesitate to do these same simple modifications again and I hope this thread helps anyone contemplating the same mods to their own cooling sytem.

 

[Blacksting]

Re: 1988 70 HP Johnson Cooling System Modification (+ Additional Work)

great job NoEcm . i'm thinking you'll save a few o/bs from destruction . joe reeves will be proud . <<<<best teacher on iboats , in and around many .