Johnson 5.5 Seahorse CD-16 cooling problem

mba2ry · May 5, 2006

This motor ran fine last year. Now, the water pees at high speeds just fine but not at all at trolling speed and proceeds to get hot. I have changed the thermostat. I tried loosening the thermostat housing at idle. No water came out there or at the pee hole. As I increased the throttle, water began bubbling out the housing and at the pee hole at the regular rate. Is it possible the water pump is weak and needs replacing?

Paul Moir · May 5, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

Welcome to Iboats! Absolutely, that is sure what it sounds like. Either that or something is clogged. When was it last changed?

Chinewalker · May 5, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

This is a not-uncommon problem if the grommet that the water tube seats into is worn, cracked or damaged. Can also happen if the unit is not deep enough in the water and is sucking air. Double check all fittings and make sure the water in the test barrel is above the lower unit bulge where the pump is... - Scott

mba2ry · May 5, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

Unknown as to when, if ever, it was changed. I will dismantle it and take a look. Or, should I just go ahead and order and replace the impeller and plate? What will I see about the impeller and the plate to tell me it is bad? As to being clogged...I am sure it is not.

Paul Moir · May 5, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

Take it apart first to see what needs to be replaced. Around here we service the water pumps and replace the impellers every few seasons (2 or 3). Sounds like you're way beyond that. Inspect the housing for grooves caused by grit, etc. If it's got them you'll need a whole new pump (~$40 dealer part). If not, you can just replace the impeller and wear plate with aftermarket parts pretty cheap (~$20). The 5.5hp engine must be removed to access the shift coupler. So you'll need a new base gasket. They're available both aftermarket and OEM cheap.

perkdp · May 5, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

Since it pumped good last year, you'll probably find one ear broken off the impeller. Or a couple of the ears fold back toward one another. If there are ears broken off, be sure to flush it well to keep all the rubber bits out of circulation.

seahorse5 · May 5, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

Change out the head gasket and re-surface the cylinder head using 220 sandpaper on a sheet of glass. The 5.5hp heads warp easily when overheated and the gaskets burn out quickly.

Scaaty · May 5, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

Paul..."The 5.5hp engine must be removed to access the shift coupler. So you'll need a new base gasket.".....I have a 61 CD 18. Are you saying you need to pull the block just to get at the impeller? My pumps fine, but that sure sounds like a LOT of work for an impeller.

Paul Moir · May 5, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

Yup. It's not that much work since there isn't a whole lot holding the engine in. But it's not surprising they fixed that little feature in '65 when they redesigned the 5.5 into the 5 and 6hp.

mba2ry · May 7, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

First, I sure appreciate all this advise. I have removed the engine and have inspected the impeller and housing. It looks perfect and quite new (???). But, I think I see the problem. When I took engine apart from the lower end, a few pieces of hard black plastic fell out. I fit it together, sort of, and it is (was) about 3/8" deep, inside diameter about 3/8", outside about 5/8+. It appears to be a collar and looks like it would fit on the copper line that goes from the impeller upwards. It makes sense that if the copper line wobbled around without the support of the collar, under fast throttle, it would force water up and through...but on idle or slow, if it was not aligned properly (with the help of a collar ??), it would not get enough water directed up the hole. I have ordered a manual and hope it has a schematic so I can see the parts and how it fits. Also to id any gaskets or seals I need to put it all back together. Unless someone has anything to support or add, I'll wait for the manual. Thanks, Bob

Paul Moir · May 7, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

That would be the seal Chinewalker was referring to. Here's the aftermarket p/ns: Head Gasket 18-2961 (OEM 329103) Powerhead Base gasket 18-2901 (OEM 313065) Impeller repair kit (includes w/p grommet and wear plate) 18-3202 I almost forgot about this, it might be some help: http://www.outboard-boat-motor-repair.com/Johnson 5.5 HP Seahorse Outboard Boat Motor/default.htm

tashasdaddy · May 7, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

while you are that far change the impeller any way. since you do not know when it was last changed.

mba2ry · May 7, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

Paul, you are saying that the broken plastic collar I was referring to is the "seal" Chinewalker referred to. Is that what is included with the Impeller repair kit "p grommet"? Does it go down next to the impeller. I can't see how it would "seal" anything. It is hard plastic. There is, intact, a rubber seal at the impeller where the copper tube comes out. There is also a rubber seal where the other end of the copper tube goes. I also cannot see this broken part anywhere on that site you referred me to. (Thanks alot for that site.) About the impeller...it looks new...has alot of "life", no wear or pit marks or anything...the area is very clean and inside the body there are no scratches or scars. I've had this motor for about 5-6 years but have only had it in the water a few times. Any more comments appreciated about that hard plastic part. Maybe it came from somewhere else. As I said, it fell out in pieces when I separated the top from bottom.

Paul Moir · May 7, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

The problem with impellers are that they're star shaped when new. After sitting in the housing for a few years (whether they move or not) they take on it's shape and stop pumping so well at idle. 5 or 6 years it's at least due for a changeout. I'm wrong about the seal, I was thinking of that rubber grommet that's set in the pump housing. I've never seen one dry out that bad, so I had doubts if you were talking about that peice as well. Perhaps the one at the top of the tube is what Chinewalker ment: those do dry out and crumble fairly often. Could that possibly be part of the crankshaft seal? There is a delicate carbon peice between the spring and the o-ring in it. It sounds like the peice you're describing is a little too small to fit the driveshaft though. Email me at paul.moir@gmail.com and I'll send you a diagram of the L/U. Probably it would make more sense for you to look it over and see if you can identify the mystery part.

mba2ry · Jun 15, 2006

Re: Johnson 5.5 Seahorse CD-16 cooling problem

Thanks to all for your advise, especially you, Paul. Engine is up and running great. Took some time due to bad sinus attacks but it is done. Now we'll see if it catches fish! Bob

Johnson 5.5 Seahorse CD-16 cooling problem

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