Overheating Johnson

Lakesailor

Lakesailor

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My bro-inlaw bought a little cuddy boat with an outboard. It ran well enough in a dustbin for 5 minutes or so, but when we took it on Ullswater the tell-tale stream became very hot and I don't think it was chucking any water out of the exhaust below the cavitation plate.
Looking at the motor the thermostat housing has obviously been off and investigation showed no thermostat in there. There are also signs of overheating around the plugs.

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He's going to take it to a dealer in Penrith, but do the forumites have any idea why it would be overheating? Just as a double-check on what he gets told, really.
The tell-tale stream is strong so I assume the impellor is OK. There is no thermostat, so there can't be a closed system there. Are any other blockages possible? Could the leg be too short? The cavitation plate does lie parrallel to the bottom of the transom. We thought of taking a couple of inches off the transom recess.
It's a 1981 long shaft 8HP 2 stroke.
Starts first pull.
 
Hi
We had a 7.5 Evinrude ( same thing really) which developed the same problem. There is a small water output on the back of the leg about 4 inches below the top cover. Does that still work? Ours got corrosion/salt deposits in the water ways - tried to take it apart but sheared the head bolts. Our local repairman just made the usual teeth sucking noises. Sorry.
 
I have a long shaft E'rude 6 a little younger at 1984 but moreless the same engine.

The pump impeller may not be as good as you think.

The engine should not be run without the thermostat, which is held on its seat by a spring (which is also missing?) and is what pressurises the cooling system.

In use the water line should be up around the ltlle cavitation plate above the extension piece. The water pump is on top of the gear case below the extesion so so long as that is covered at all times that is not the cause of your problems.

I have had troubles with the cooling, much as you describe, which has been caused by corrosion around the gromment at the top of the water tube from the pump to the power head squeezing the rubber over the top of the tube. It you push a wire up the tube once the lower unit is removed you can feel it if that is the problem. Rather than coming up against something solid you hit something squidgy!

It is vital that the extension piece is removed with the gear box when you remove the lower unit as bush that the drive shaft runs in at the top of the extension combined with crud on the shaft will try to pull the shaft out of the pump if you separate the joint between extension and gearbox. The key between the impeller and the shaft then smashhes the top of the pump housing (you get away with it, just, if the key is plastic as it f00ks up the key but if it is an OMC original metal key it is the pump housing that gets f00ked.

The parts diagrams on the BRP website are useful although not a substitute for a muanual. The grommet is item 69 on the exhaust housing parts diagram and is called "water tube retainer".

I did have some difficulty with the engine ID as there does not seem to be an 8hp model listed for 1981 so I looked at 7.5hp. You can check the year from the model (not serial) number. The word INTRODUCES is the key where I=1 N=2 etc up to E=9 and S= 0 So an 81 model will have the letters CI in the number and an 82 model will be CN etc Other letters are J for Johnson (E for Evinrude) S for Sail version, R for rope start, L for long shaft. A letter after the year code is not significant. The number after the J is the hp (and even the 7.5 has an 8 there)

For a heavy displacement hull, which that obviously is, you might be better off with the 9¼ X 6½ prop that was fitted on the sail versions
 
Good information there and all adds up. The higher outlet below the power head has rust stains, but no water running.
The dealer he is taking it to is a Johnson dealer so hopefully he will be able to dismantle it without too much damage.
The lack of thermostat sounds like an attempt to overcome the overheating that has, in fact, exacerbated the problem.
 
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The higher outlet below the power head has rust stains, but no water running.

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You don't normally see much water coming from there. The bulk of the water leaves via the exhaust outlet behind the prop. There I do notice a difference from mine, which is the sail version. Mine has a large cavitation plate on the extension similar to the one on the gear case and two exhaust outlets immediately below it so that when going astern the gases don't get drawn into the prop.

You should have a good strong jet of water from the "pee hole" in the back corner of the lower engine casing, but since that comes the pressurised side of the cooling system it probably wont be so strong with the thermostat removed. Also because it is on the pressurised side don't enlarge the hole or run without the nipple being in place. In salt water of course it gets blocked now and then.

I hope your Johny agent can sort it out without to much expense. Sometimes though they won't look at engines that old.
 
My old evinrude 4 regularly cut out when used at high power over a long period. Tried everything without success. Article in boat mag prompted me to try clearing out the cooling system, so removed head. Waterways were severely restricted with salt deposits. Cleaned out salt with thin wire,reassembled with new gasket and has been fine since.
 
Good luck to your friend in taking it to the dealer. They often really are only aligned to servicing new motors. The problem with old motors is the corroded bolts (SS into Al) that shear off rather than unscrew. You end up paying a dealer to snap the bolts off for you so he can sell you a new motor.
I am not so much criticising the dealers who have to make a living but pointing out that old motors can require real labour and luck to keep them running. The first thing I would advocate is that your friend try to remove every bolt in sight. They are 3/8 inch SAE heads mostly. But don't use anything longer than a 6inch spanner. Even then if it is really tight use heat and or lots of penetrating oil and hammer. If you snap a bolt off you are usually looking at operating in future without that bolt or burying the whole motor. Refit all bolts with Duralac or lots of grease and remove them every few years.
As for the problem itself. I dunno. replace the thermostat. Then if it still gets hot remove the cylinder head and clean out the passages. It is actually quite easy to remove the cylinder head once you get the bolts loose. Mine 82 6Hp gives regular trouble with blocked tube from pump to power head but the symptom is no water from tell tale. good luck olewill
 
I know what you're saying Will, but I need to treat this at arm's length. As it's my brother in-law's motor and he lives nearly 30 miles away (which is an hour's trip up here) I don't want to get too involved. Added to which if I break a bolt then remedial work is all my responsibility. If the dealer does then brother in-law ends up paying, but family relations don't get strained.

We've all been in the "Clever [--word removed--], he's bust it now. I wish I'd let an expert look at it" situations haven't we? From one side of the fence or other.

Jesus, is Mary Poppins running the swear filter now?
 
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30 miles away (which is an hour's trip up here)

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If had you experienced life in the London area that would hve been " which is ONLY an hours trip up here."

You lucky barsteward.
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Jesus, is Mary Poppins running the swear filter now?

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Careful or they will switch on a blasphemy filter as well
Anyway Jesus is not a registered user so even if he reads your question he won't be able to reply! /forums/images/graemlins/wink.gif


As usual I agree with Will. A friend took an old Yamaha to his local OB mecahnic because he was having difficulty undoing bolts. The OB man broke all the bolts on the themostat/ exhaust manitold cover (9 of them IIRC)
 
Johnson is not in my double-entendre vocabulary. It's a little early for me and has overtones of "ever-so-slightly-amusing" Radio 4ness.
Now if there had been an ouboard manufacturer called Willy I think I could have worked one in. /forums/images/graemlins/shocked.gif /forums/images/graemlins/blush.gif
 
My 4.5 Johnson Twin ..... service guy said - No mate .... suggest you get a manual and DIY ..... if I do it - most likely get expensive with bolts sheering etc. etc.

It's a bind as well - as it starts / runs nice .... just blocked waterways ....

I did all the fresh-water flushing etc. - but still it blocked ...
 
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I have had troubles with the cooling, much as you describe, which has been caused by corrosion around the gromment at the top of the water tube from the pump to the power head squeezing the rubber over the top of the tube.


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Hit the nail on the head there. Back from the dealer and it was the grommet blocking the water passage down the leg.
He charged my bro-in-law £70, for the strip down, checking scraping out blowing and flushing. and reassembly, which I thought was a very good price.
 
Thanks for letting me know that. It seems to be a bit of a design flaw. At least now he knows about it. Last time I did mine I modified it using nylon spacers and O rings but only time will tell if it's an improvement or not. The trouble is that it is not easy to get to as both the powerhead and the lower unit have to be removed.
 
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