1975 115 hp Johnson

[bm9913]

Last year I bought a 1975 115 hp johnson. After I got it started, it began overheating, or at least the warning sound went off and the engine wasn't spitting any water. So I replaced the water pump, which didnt stop my problem. So then I replaced the vernatherm (thermostat). I put the boat on the lake it ran fine for about 30 mins, but as soon as I turned the throttle down from full to idle, the warning alarm went off agian and I noticed that it had stopped spitting water. So what else could be my problem? I was also wondering if I could run the boat without the vernatherm? You can run a car without one but how about an outboard? PLEASE HELP!! This thing is driving me crazy...Thanks

 

[iwombat]

Re: 1975 115 hp Johnson

Did you do the whole waterpump, or just the impeller?

Did you backflush the cooling system out when you had the vernatherm cover off?

Did you check the condition of the water deflectors under the heads?


If you run w/o the vernatherm it'll run too cool and you'll have a whole different set of problems. This problem should be fairly easy to solve.

 

[bm9913]

Re: 1975 115 hp Johnson

I replaced the whole water pump. I did not back flush...would you do that simply by running water back down the tubes from the vernatherm? And Ive never even heard of the the water deflectors. What are they..and can you see them when you have the vernatherm housing off?

 

[iwombat]

Re: 1975 115 hp Johnson

You can flush the motor out by just dropping the lower unit, removing the hoses off the heads, and hooking a hose up to the water tube. That will forward flush, and it's easier than disassembling your vernatherm housing.

The deflectors are short pieces of hose placed in the water passages in the heads. They direct water to circulate through the head properly. Since this motor has overheated you're probably better off popping the heads off and replacing the head gaskets anyway.

However, if it's stopped spitting your problem is either in the vernatherm, a blocked water passage, or the water pump.

Edit: Have you considered retrofitting a tell-tale as per the FAQ? That would at least tell you if the pump and cooling passages are ok.

 

[bm9913]

Re: 1975 115 hp Johnson

Thanks ill give the flushing a try tomorrow. How hard is it to remove the heads and replace the gaskets? Im still a rookie at all of this, but Im learning...When I replaced the vernatherm, the kit that I ordered didnt come with the two springs that are inside the housing, so after inspecting them I resused them...Could this possibly lead to my problem? Is there anyway to test that the water pump is working when I have the lower unit dropped?

 

[iwombat]

Re: 1975 115 hp Johnson

Replacing the head gaskets is dead simple, you'll need a torque wrench for putting it back together though.

 

[F_R]

Re: 1975 115 hp Johnson

Far too much blame is placed on thermostats. If you have all the parts in there, it should work.

Could be the deflectors, but my guess is that there is a problem with the water pump installation or there is a a leak in the return water tube grommet. Did you make use of the two plastic water tube guides when you reinstalled the gearcase? Just a best guess.

 

[iwombat]

Re: 1975 115 hp Johnson

The weird part is that it didn't overheat for 30 minutes, and not until the RPMs were reduced. That means the LU assembly is at least mostly correct. Maybe the grommets aren't in there proper or something.

Although, at high RPMs the vernatherm is bypassed by the poppets anyway. So, maybe there is a t-stat problem after all.

Process of elimination time.

 

[bm9913]

Re: 1975 115 hp Johnson

When I mount the Lu back up, I use the plastic guide sleaves to guide the two pipes into the "holes" in the water pump. But how can I be sure that they meet up perfectly? The two pipes both move freely a 1/4 inch or so back and forth...and the ends of both seem to have at one time or another been pulled on or slighty bent in, then back out again. I have wondered many times that this could be my problem or at least a part of it, but I dont know how to check for sure.

 

[iwombat]

Re: 1975 115 hp Johnson

You kind of have to hope you did it right. That's where the tell-tale comes in. Also, if you used the new superseeded waterpump kit the new impeller plate effectively blocks off the return tube anyway.

 

[bm9913]

Re: 1975 115 hp Johnson

Thats the kit that I used. At the time I wondered why the plate blocked off the retun hole. Now I know. The weather turned bad here agian so it will be a few days or so before I can get back to work on it..due to the lack of a garage..As soon as I get started on it again...Im sure Ill be getting back to you all. Thanks!

 

[dreadinger]

Re: 1975 115 hp Johnson

I did the tell-tale mod on my 1975 115hp last weekend, it is very easy to do.

 

[bm9913]

Re: 1975 115 hp Johnson

Thanks, Im going to be attempting the tell tale here soon as well, Ill prob have some questions about that too