1987 Johnson 110hp overheat problem- need diagnostic ideas.

[Ridgepatrol]

Hello, I'm in need of diagnostic ideas on how to trouble shoot an overheat problem I had yesterday.

Background: 1987 Johnson 110hp, owned since new. The motor is on a 16ft shallow bottom waterski boat. The motor has very few hours on it, as it only gets used 3-4 times per season when we are up at the lake. The boat has always been stored inside on the trailer.
I last used the boat last year in October, and everything seemed to work fine. The motor has never had any work done to it, other than regular maintenance like plugs and lube.

Yesterday we put the boat in the water, and were put-putting down the harbour channel to go out into the lake, when I noticed the temp gauge moving towards the hot side. The overheat horn then started to sound, so I shut it down and paddled back to the dock.

During the overheat episode, the tell-tale water stream was running continuously, but it appeared that no water was coming out of the upper exhaust ports.

So my thoughts are:
1) faulty water pump
2) faulty thermostats
3) plugged water intake or exhaust.

For now I am looking for ideas on how to diagnose these problems without tearing too far into the motor.

Can someone with some experience please advise?


Also, I doubt this would effect anything but last fall I changed the prop to a stainless model, designed for this motor, and it appeared the same as the factory prop.

Thanks,
Matt.

 

[AEROCOOK]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

I would start with the water pump impeller if it hasnt been replaced recently. This may or may not be the cause of your problem but it's routine maintenance that should be done periodically. I've heard that it should be done annually if running in salt water and or using the motor frequently. After changing the impeller try taking it for a slow cruise and periodically monitor the temp of both heads with your hand to see if both banks are the same temp, if one is hotter than the other, it may be time for you to replace the thermostats. it's a bit of a P.I.T.A. one the V4 motors, especially the bubble back models like yours.
BTW I'm not far from you (Innisfil) and I have the same motor.

 

[Ridgepatrol]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

Thanks for the quick reply.

Before I go and take the lower unit off is there a way to check for water flow at the thermostat housing?

Can either of the two hoses from the thermostat be removed and water flow checked that way ?

 

[AEROCOOK]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

I'm not sure if there's a procedure for testing water flow, I've never done it but others may be able to help. Not to sound like a broken record but if the impeller hasnt been changed in the last 2 years, just do it regardless of anything else... That's my 2 cents worth, good luck.

 

[emdsapmgr]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

The telltale indicates that the water pump is working, at least to some degree. If the stat(s) stick closed, the water cannot circulate thru the powerhead and you will get an overheat for sure on at least one head. A laser temp gun will help you hunt the problem. If only one head is hot, it's likely the stat. If both heads are hot, could be stats, impeller, or debris in the system. Probably best to replace the stats in pairs.

 

[Ridgepatrol]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

I had it running this afternoon on the muffs.

When I first started it up, I could feel the cool water circulate up behind the bubble back between the two cylinder banks. The tell-tale was steady and had good pressure.

I then let it sit and idle and warm up.

The stream from the tell-tale got increasingly warmer.

I got out the laser thermometer and found that the port head was running at about 15OF and the starboard head was quickly nearing 190F, and I saw as much as 205F when I shut it down.

Me thinks it is a thermostat, what do the rest of you think?

I have had it idling many times while on the muffs, but I can't seem to remember whether there should be water coming out of the upper exhaust ports, should there be?

 

[Ridgepatrol]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

What direction does the water flow?
From the thermostat housing to the heads or heads to thermostat housing?

 

[Ridgepatrol]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

bump

 

[wayneo99]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

run it with the hoses off the t-stat housings and see what kind of flow you get from each head

 

[Daviet]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

Sounds to me like you need to replace the t-stats.

 

[Ridgepatrol]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

So if I take the hoses off the T-stat housing, the water should flow out from the heads ?

Is that the normal flow direction-- heads down to the T-stat?

 

[emdsapmgr]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

A 150 temp on one head is normal at idle. The high temp on the other head indicates a problem/restriction. You will get a hot horn once either head gets up to 212. The horn will silence when the head temps get back down to 175. 175 is still too hot. The cooling water circulates through the powerhead to the thermostat housing. At idle the water from each head has to go through it's own thermosat before it dumps back into the exhaust housing. Sounds like the starboard stat is stuck shut. If the stat sticks shut, no water leaves that half of the block and no new water comes in. Replace the stats. Water will come out of the upper exhaust ports when the stats open.

 

[Ridgepatrol]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

Thanks for everyone's help, I have determined the problem to be either the thermostats or a restriction in the water outlet.

I ran the motor without the hoses connected from the head to the t-stat housing.

I had excellent flow from both sides, and the temp on both heads was around 105F since the motor would not warm up.

So I will order a t-stat kit.

Can someone advise which repair kit manufacturer I should use? This site lists the Sierra brand, do they have good products, or should I be ordering from BMP?

Also, can someone advise as to what the torq specs are on the t-stat housing bolts?


Thanks again,
Matt.

 

[cfauvel]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

Thanks for everyone's help, I have determined the problem to be either the thermostats or a restriction in the water outlet.

I ran the motor without the hoses connected from the head to the t-stat housing.

I had excellent flow from both sides, and the temp on both heads was around 105F since the motor would not warm up.

So I will order a t-stat kit.

Can someone advise which repair kit manufacturer I should use? This site lists the Sierra brand, do they have good products, or should I be ordering from BMP?

Also, can someone advise as to what the torq specs are on the t-stat housing bolts?


Thanks again,
Matt.

Matt I don't know the torq settings, but do be careful I busted one of the bolts for the t-stat cover in the block once, tighten them just enough to seal them, better that they leak than bust the bolt.

 

[Ridgepatrol]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

Yeah I hear you on the tightness. Better to have it loose and leak, because you can always tighten it a little more, than to snap a bolt.

Do the gaskets get installed dry, or should I put some gasket sealer on them?

 

[AEROCOOK]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

Yeah I hear you on the tightness. Better to have it loose and leak, because you can always tighten it a little more, than to snap a bolt.

Do the gaskets get installed dry, or should I put some gasket sealer on them?

I used a little bit of silicone on the gaskets mainly because it helped keep things glued together during install. There are 2 springs and 2 relief valves that you need to hold in position while reinstalling so it helps if you dont have to fiddle with the gasket alignment as well. I replaced mine for the opposite reason that you have... My port side was running too cool as compared to starboard which was normal. When I took the Tstat block off there was no Tstat on the port side. I found it wedged down under the powerhead, presumably it fell out when the last person was doing the job and they didnt notice.

 

[emoney]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

I'm not a fan of the Sierra Tstat kits for these as Jonnyrudes are particular about them. Try and find the OEM part as it's still readily available. If noone has weighed in with the torque on the bolts, I'll repost after work after I look it up in the manual (which is a great investment, by the way).

 

[ryguy1101]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

...and be extra careful to not break off the T-stat housing bolts during removal. They tend to corrode pretty easily but thankfully, it looks like you run in fresh. If you do, the powerhead has to come off to finish the job.

 

[wayneo99]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

the intermediate housing is plastic, order a new on and use some heat on those bolts to make sure they dont break off.

 

[itsaboattime]

Re: 1987 Johnson 110hp overheat problem- need diagnostic ideas.

I have the same outboard, except mine is an Eveinrude. The starboard bank always runs hotter on muffs. But not that hot.
My advice is if your goin to replace the T-stats, save yourself some heartache later and do the waterpump. Dropping the lower unit isn't that hard. Toughest part is the shift linkage under the carbs, and that isn't all that hard. I swap out the waterpump every two years and check my t-stats at the same time. I change them as needed. 1/4 inch drive tools are the key to the t-stat cover bolts. They are small enough to get in there, and you won't twist off the bolts(unless your Hercules).
The last thing you need is part of that rubber impeller breaking off and lodging itself in the water tube or somplace in the water passages of the power head. Then you ARE talking about alot of work.