overheat alarm coming on

[Kajun37]

well i'm out of ideas to fix this problem...maybe you guys can help me out.

1994 Johnson 140 j140txerr

i was given this motor from a guy that repowered because of this same overheat alarm problem...

when i got it mounted on my boat i took it out for a sea trial....when i put it WOT about 43mph....after a couple mins the overheat alarm comes on...i imediately turn it off and pull cover off and touch heads...and find that i can hold both hands on the heads no problem......pisser is peeing great and strong.....i start it up again and go to take off and it ran like crap...latter i find out about SLOW mode.....so this wasnt a problem......i bring it back home and rebuild all 4 carbs, i buy 2 new thermostats and 2 brand new thermo switches. i have the VRO totatlly disabled since i got the motor..capped and unplugged...so the only possible continious alarm will be the overheat alarm..which is controlled by the thermo switch....

today after doing the carbs and replacing the thermostats and thermo swtiches.. i drop it back in water...adjust my carbs according to manual...sounds great....i take off for a run...i run it about 20 mins at 35mph...no problems..no alarm...i decide to take it to WOT at 43mph...a couple mins into WOT the alarm goes off again... i shut down , take off hood..touch heads...i can hold both hands on heads again...not overheating...pisser is working great ....i start and kill it a couple time to get it out of SLOW mode....and take off again...rode around for another 20mins at 35mph and under...purrs like a kitten.......bring it back to about 40mph and the alarm goes off again.... do same checks..not overheating and pisser works...get out of SLOW mode again and this time i ride around for 30+mins at under 35mph.

as much history of this motor that i know...

march04 the guy had pistons resurfaced, new head gaskets

june04 new driveshaft bearing/housing...

may04 new thermostats and thermo sensors

also when i picked up motor the guy tells me he had lower unti rebuilt and new water pump done within last year or so...

compression is 120/125/125/125 ...great spark on all 4..jumps a 7/16 gap

any ideas? :/

 

[DJ]

Re: overheat alarm coming on

If I were you, I'd look at the water pump myself.

 

[JUSTINTIME]

Re: overheat alarm coming on

have u tested the sensors?
make sure the vro pump wires are not touching
could be the water pump housings
best way to tell would be a water pressure guage

 

[Texasmark]

Re: overheat alarm coming on

My engine is Merc but it has 2 water flow systems. One is thermostatically controlled and the other is pressure controlled. The latter is much larger in diameter.

If you get this alarm when running at wot you may not be getting adequate circulation to support it (the engine) if you have both systems.

But conversley, the fact that the engine is cool is confusing in that the over temp sensor for me shorts at 195F and you surely would detect that heat. Would imagine yours is pretty close to that.
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Depending on your system of plumbing the peeer might just be telling you that the impeller is pumping, not that your engine is necessarily getting anything from it; i.e. like on mine the pee comes from the exhaust water jacket which has to get water all the time, and when my thermostat froze closed and I was at low speed, the engine overheated (alarm sounded).
-------------------------------------

My temp sensor shorts the sense wire to ground (head/waterjacket cover) to activate the system.

Since you seem to be confident that the engine is not overheating, why not pull both sensors from their mounts (open circuit essentially) or pull the wires from them out of their sockets and make your 40+ run. Then replace them one at a time and take data on what happens. Might be an interesting test.

If the alarm goes off with both out of their sockets then your problem is elsewhere and that answers the question as to why you can't find it....looking in the wrong place.

So where to look?

Merc uses a warning module for monitoring temp and oil. Yours could be bad.


So what's different at the two speeds? Water pressure, a little more engine heat, and engine rpm's. Engine rpm's.............Hmmmmmm.

Mercs that have an overrev limiter have it wired into the warning module. I don't have one but I assume the alarm sounds if you overrev, besides the slow mode thing like you mentioned; don't think Merc has that.

What are your engine rpm's at 43 mph? Possibly if you have one it could be the culprit.

Pull the temp sensors and if you fail that test (sounds off with them removed) you have 2 more places to look and I think I would look at the overrev limiter (if you have it) first. Course the thing that generates your SLOW operation could contain it.

If you can find a rev limiter wire going to your warning module (if you have them of course) I'd pull it just to run a test to see if the alarm quits with the wire removed.

Keep us posted and good luck,

Mark

 

[Texasmark]

Re: overheat alarm coming on

Bump

 

[Bert]

Re: overheat alarm coming on

I'm going thru the same thing with my 150 Johnson. I used an infared gun to check the temperatures and found that one side is running 20 degrees hotter than the other. I'm running vinegar thru it( search some old posts on this board)and it's supposed disolve deposits and buildup. Make sure of your problem before you do anything drastic.

 

[Walker]

Re: overheat alarm coming on

You've done a lot of work to it but you haven't done the most obvious. Put a new waterpump in her.

 

[Kajun37]

Re: overheat alarm coming on

thanks for the replys...i have a complete waterpump kit and housing on order.....hopefully this fixes it....the guy that gave me this motor said he replaced the waterpump and it didnt fix the problem..and said it was about year old with hardly any use on the pump.. thats why didnt change it out.. but i should of known better and did that first .

if it doesnt fix it i'll start looking at water circulation.....

texas..my tach is kinda screwy at the moment..i dont think it works right on this motor...it would flucuate alot...but at 43mph i had about 5200 rpms or so i think...wasnt relying on the tach much since it was flucuating alot.

 

[Texasmark]

Re: overheat alarm coming on

Well, you shouldn't be bumping anyover rev limits at that speed as long as they are functioning normally.

'94 with only one impeller change back when the engine was only one year old would certainly spell trouble here in the fall of '06. Guess I didn't realize what you said there. :% Among other things, when the engine sits, without the drive shaft being periodically rotated, the rubber impeller can take a set. Being eccentric, when the short side comes by the long side to start the water's travel thru the pump, it doesn't pick up much water as the blade tips don't touch the side of the pump.

Mark

 

[Kajun37]

Re: overheat alarm coming on

i'm not sure if there is a overrev limiter on johnson's, hadnt heard anything about that...anyone know?

the waterpump is only a year old now...with little use......its been changed regularly throughout its life....maybe it wasnt installed right or missing a oring or something..hopefully lol

 

[clanton]

Re: overheat alarm coming on

You should check the waterpump housing with a currant parts book. Housing for V4, and V6s used to be the same. Not true now. Insure you have the correct water pump kit with housing.

 

[habu]

Re: overheat alarm coming on

Kajun37. I am also having similar problem on a Johnson 150. Was wondering what that "slow mode" was that you speak of. Think I found my problem, have excessive water leaking, under pressure, when run at idle with the hose and earmuffs on. suspect the water pump or gromets on the water tube. Tearing it down now to investigate. Pisser peas like an old man with a bad prostate. Al

 

[alden135]

Re: overheat alarm coming on

Are you sure it's an overheat alarm and not a fuel restriction alarm?

Edit: nevermind, reread your post.

 

[Kajun37]

Re: overheat alarm coming on

well my water pump kit should be in tommorow..so tonight i went ahead and took off LU and took off waterpump.....everything looks brand new..housing/impeller...only thing is i cant take off the impeller..it wont slide up off the shaft..i'll prob cut it off or something......

clanton....the housing is the one that my parts book shows part# 435959..btw..i'm moving to panama city next august cant wait!

question....my service manual say i need a few types of sealants and stuff to put the water pump back together.

OMC adhesive M sealant
OMC gasket sealing compound
OMC triple-guard grease
OMC neadle bearing assembly grease


do ya'll buy this OMC stuff or do ya'll substitute? if so what do ya substitue with?anything i can do without?

 

[Walker]

Re: overheat alarm coming on

Get a good grip on the drive shaft with a rag or a glove and while holding the impellor turn the drive shaft counterclockwise. The impellor should get free unless its corroded to the shaft.