89 Johnson 70 hp over heating issues (slow mode)

[scsdiver]

we have been chasing a overheating issue for longer than i would like to admit. we have installed a new waterpump impellor/housing and seals, we have replaced the thermostat as it was corroded and not working, we have performed the tell tale relocation, we have removed the exhaust manifold cover and found it to be full of scale and other junk which we removed and cleanout out all of the scale and made it look new again. we really do not believe our problem is the impellor or waterpump as we have good waterflow to the top of the block, it has a good strong flow out of the tell tale. however not to long after getting under way and running up around 3000 rpm for about 3-5 minutes the motor goes into slow mode. once we have made changes we had hoped to fix it the area we have taken it to run it it goes into slow mode at almost the exact same distance every time. it would almost seem as though power pack was bad. we have also replaced the temp sensor as it was bad. the only reason i do not believe it is the power pack is there is steam coming out the upper exaust ports which i assume means we are boiling water in the head somewhere. my next thought to try and end this is to run the motor in a high concentrate of vinegar and water until it breaks down the scale that must be inside the block and probably the water tube. im not opposed to pulling the head off but i would rather not if i do not have to. any body have any thoughts, ideas, suggestions that i may not have thought of. just to give you a little history on the motor the original owner lived on a lake and used it in fresh water only. he pulled it out and had the intention to rebuild the boat but lost interest and after sitting for 2.5 years we acquired it. the odd part of the motor is that it does not always happen ( slow mode that is) we took a trip to the keys and used the boat in some really rough seas and deff rough conditions for the motor and had no issues with it going into slow mode. we went out about two or three times after coming back and i believe it happened one time out of three however the last three times we have been out it happened every time.

 

[boobie]

Re: 89 Johnson 70 hp over heating issues (slow mode)

Two things, get a temp gun to measure the temp on the top of the block. Harbor Freight has them for very cheap and that will take the guess work out of it. Power packs can go into SLOW for no apparent reason. Been there.

 

[durban]

Re: 89 Johnson 70 hp over heating issues (slow mode)

on the over heating , did you clean the holes on the exhaust side there are 3 little holes where where the water goes into the block & also on the bottom end where the water comes from the tube into the exhaust box there is another hole towards the side feediding water from the bottom , i would take the poppet valves & thermostat out & run it to see if there are any changes in temp then put them back after you found problem .

 

[Faztbullet]

Re: 89 Johnson 70 hp over heating issues (slow mode)

This is the lost foam cast block and water flow is different than the 49ci motors and t-stat is also the poppet valve. Removing t-stat/poppet on this model will cause it to actually run hot!!! This isnt like old models as the passages and exhaust are cast into block and it only has a water jacket outer cover.

 

[scsdiver]

Re: 89 Johnson 70 hp over heating issues (slow mode)

Thank you guys for the comments. Faztbullet is correct the block has the water jackets cast into it. when we removed and cleaned out all of the scale i think we may have been a little ignorant thinking the scale was contained to the exhaust manifold. when we first opened the manifold up the small holes from the head the manifold where clogged there is a total of five that i found. three of them where completely scaled over and clogged. after cleaning there appeared to be a pretty good flow of water coming out of each hole. i guess i keep reffering to it as a exhaust manifold to but your right it is the water jacket cover. i was about to pull the thermostat and try running it to see if it makes a difference so glad i had not tried that. we bought a ir temp gauge already and we were deff overheating before cleaning and i did not even think to try it again i just assumed we still had scale issues. i will take it out and try it tonight.

 

[turbo4door]

Re: 89 Johnson 70 hp over heating issues (slow mode)

What temp range should we be looking for on the top of the block when it goes into SLOW?

 

[steelespike]

Re: 89 Johnson 70 hp over heating issues (slow mode)

Does an 89 have a slow mode? I would guess no.
Im thinking your losing a cylinder. But I have no experience with the 70.

 

[fishfeatures]

Re: 89 Johnson 70 hp over heating issues (slow mode)

you say you are setting steam from the upper exhaust ports ... how is the water from the tell tale when it starts to act up ?is it hot to the touch ?

 

[turbo4door]

Re: 89 Johnson 70 hp over heating issues (slow mode)

Does an 89 have a slow mode? I would guess no.
Im thinking your losing a cylinder. But I have no experience with the 70.

Everything I've read suggested that we are in SLOW mode, especially that we get a limiter at exactly 2500rpm.

We also are not 100% sure that its an 89, could be a 90-91. Is there a way to tell for certain?

 

[turbo4door]

Re: 89 Johnson 70 hp over heating issues (slow mode)

you say you are setting steam from the upper exhaust ports ... how is the water from the tell tale when it starts to act up ?is it hot to the touch ?

I'd call it warm, certainly not hot. I could hold my hand under it all day and be comfortable if that gives you an idea

 

[turbo4door]

Re: 89 Johnson 70 hp over heating issues (slow mode)

Also as a side note, and probably should have been mentioned in the original post, this motor has been converted from a VRO pump to the standard pre-mix pump and we are premixing 50:1 in the tank. This was done by previous owner. We have rebuilt the fuel pump as of three days ago as well.

 

[ob]

Re: 89 Johnson 70 hp over heating issues (slow mode)

Post the model number off of the transom bracket so we can be sure what year model you have. 89' did not have S.L.O.W feature to my knowledge. There will be a CE in the model number if it is a 89' model.


edit: Ah ,I stand corrected... as a bit of internet research reveals that the s.l.o.w. feature was introduced in 88'.

 

[WernerF]

Re: 89 Johnson 70 hp over heating issues (slow mode)

Does an 89 have a slow mode? I would guess no.

Yes, as from 1989 the 70hp has SLOW mode.

What temp range should we be looking for on the top of the block when it goes into SLOW?

The temp sensor (triggering the horn and SLOW) closes at 203?F +/- 6?F. On the block it's roughly the same temperature as at the temp sensor. If the cooling system works properly you shoud have 140...150?F on the block at slow speeds. When speeding up it's normal that the temperature drops a little.

It appears that the power pack's SLOW circuit can degrade with age. I've read a number of threads about it and also had a hard time with my own engine (1989 60hp) to find out (it took a whole boating season).
Some things come into my mind:
1. What about the warning horn? Is it working? Falsely triggering SLOW mode can be discovered easiest with a functional horn.
2. Make an experiment: Run the boat from the very beginning with the cowling off next time. That would prevent the power pack to warm up. Does it take longer then for SLOW to come? That would indicate a power pack problem.
3. Depending on the weather some steam out of the exhaust ports at slow speeds can be normal.

 

[turbo4door]

Re: 89 Johnson 70 hp over heating issues (slow mode)

Yes, as from 1989 the 70hp has SLOW mode.


The temp sensor (triggering the horn and SLOW) closes at 203?F +/- 6?F. On the block it's roughly the same temperature as at the temp sensor. If the cooling system works properly you shoud have 140...150?F on the block at slow speeds. When speeding up it's normal that the temperature drops a little.

It appears that the power pack's SLOW circuit can degrade with age. I've read a number of threads about it and also had a hard time with my own engine (1989 60hp) to find out (it took a whole boating season).
Some things come into my mind:
1. What about the warning horn? Is it working? Falsely triggering SLOW mode can be discovered easiest with a functional horn.
2. Make an experiment: Run the boat from the very beginning with the cowling off next time. That would prevent the power pack to warm up. Does it take longer then for SLOW to come? That would indicate a power pack problem.
3. Depending on the weather some steam out of the exhaust ports at slow speeds can be normal.

Werner,

Thanks for the help, its truly appreciated!
We have not seen temps anywhere near that on the motor. The highest I have seen with a cheap IR thermometer personally is 172 degrees, my counterpart says he remembers seeing 180 at one point. Typical range on the block temperature is 146-156 degrees. This is at idle or after running the motor and having it enter SLOW.

Unfortunately we do not have a warning alarm. We purchased the boat without it. I'm trying to find some info on how to wire one up so we can use it to help us asses the problem. If anyone has any info on how to wire, or where to acquire the alarm itself (or if we can use some other alarm horn) it would be very helpful.

Will try your suggestion about the cowling-off experiment as well.

The weather here has been mid-50's...water temp in the mid to upper 60's.

 

[WernerF]

Re: 89 Johnson 70 hp over heating issues (slow mode)

...Unfortunately we do not have a warning alarm. We purchased the boat without it. ...

How do you control shift and throttle? Don't you have the OMC remote control box? The warning horn is located there.

Yes at 55?F (ca. 13?C, I love Wikipedia) my engine also steams a little at slow speeds.

 

[turbo4door]

Re: 89 Johnson 70 hp over heating issues (slow mode)

How do you control shift and throttle? Don't you have the OMC remote control box? The warning horn is located there.

Yes at 55?F (ca. 13?C, I love Wikipedia) my engine also steams a little at slow speeds.

When we got it, the horn was disconnected. We tried to wire it up to test if I remember correctly but couldn't make it sound.

The picture in the link is the alarm we had/have
http://forums.iboats.com/sea-nymph-boats/warning-horn-19-5-gls-1989-a-359392.html

 

[WernerF]

Re: 89 Johnson 70 hp over heating issues (slow mode)

Ok, this horn doesn't make an initial beep. It would need a third wire (ground) to do so.
I doubt this horn would work in combination with a VRO, but it doesn't matter for you since the VRO is disabled.

The purple wire is +12V from the key switch, the brown (tan) wire leads through the engine harness to the temp sensor in the cylinder head and to the power pack's SLOW input. With the key in run position you should have 12V on the purple wire referred to ground. Now connect the tan wire at the temp sensor with ground. The horn should sound. If it doesn't, find a replacement horn asap. In the meantime you may replace the horn with a 12V 2W (or 5W) incandescent lamp. It's better than nothing. Don't go on the water without any overheat alarm.

 

[scsdiver]

Re: 89 Johnson 70 hp over heating issues (slow mode)

So last night we ran it in a tub of vinegar and intend to continue this tonight. we noticed a considerable amount of deposit that came out so there is deff some crud in the block! we ran it four times last night for about 15 minutes per run. the highest temp we saw anywhere on the block was 150-155 on the IR temp gauge. the water coming out of the tell tale never reached any what i would call hot temp maybe warm at best. i am going to wire up a sounder as soon as i get home today thank you for that little tid bit. if you dont mind just so i am clear on the wiring essentially the purple wire is the 12+ feed to the sounder and the tan wire would be the 12- when it enters slow mode or overheats but when the motor is cold or not in slow mode the wire should have no continuity to ground? i think today after we run it a few more times in the vinegar tub we will take it out and run it and try it with the cover off and see what happens. THANK YOU FOR ALL THE HELP!!!!! im sure you can understand how frustrating a issue like this can get and we deff appreciate your wisdom.

also i wanted to add that it is a 1989 johnson 70 the serial number is TJ70TLCEM.

we also do not have OMC Controls we have the Morse controls that came with the Tracker and i belive my counterpart put a link of the horn we had.

 

[WernerF]

Re: 89 Johnson 70 hp over heating issues (slow mode)

...and the tan wire would be the 12- when it enters slow mode or overheats but when the motor is cold or not in slow mode the wire should have no continuity to ground?...

That's correct.

 

[phillnjack2]

Re: 89 Johnson 70 hp over heating issues (slow mode)

Now i know your getting it a touch cleaner with vinegar, but its not much good to be honest.
you need a proper descaler.
Nitric acid is what you realy need ,diluted at 25-1 with water.
or you could just get a product called salt away. recently i used harpic toilet cleaner for descaling the outside of a
outboard engine gearbox that was so scaled up you could see any paint.

Vinigar rinse is good once an engine is already getting a decent flow of water etc, but it sounds like you need a bit
more of a stronger product to be honest.

Kettle descaler is no good as it needs to be boiling, and salt away even comes with an attachment
for cleaning the engine on muffs.

can you tell us how much vinegar are you putting in the tub ?
and is it diluted or neat ?

your engine should run normally at about 50c to 55c (122f - 135f ) is normal at high speed.
slow or nuetral will be a touch hotter at about 60c to 65c (140 f to 150f ).
thermostat opens fully at around 62c (143f )



phill......