overheating 91 70hp issue

[fishfeatures]

I had an over heat problem with this motor recently and it has started again

It has a new impeller pumping at over 15 psi at wot and 5-6 at idle ( gauge only goes to 15 but was told before that anything lower than this means time to change pump out. It goes off the scale so reckon 18 + psi)

A new stat has been installed and checked to see if it opens in hot water.

Block has been flushed out w/o the lower unit on and all is fine.

Head too has been flushed out and again seems fine.

Head sensor has too been tested in hot water and it does read Ohms when water heats up.

I have no temp gun or heat sticks unfortunately so can't test when it's hot.


Anyway past two evenings after going at 1/4 -1/2 speed for 20 mins or so then into WOT to get to another fishing spot , the alarm has gone off. If i shut it down and wait 10 mins alarm is gone and so i head back to the dock (never too far away). Something is causing it to go into overheat and because once it cools down i think it has to be hot for sure. Now it's then pump or stat or blockage and all these check out.

Can anybody offer some other insight please, it's got to be something simple.


Oh without stat, it goes fine.... which led me get the new one..but i can't run it without the stat the difference in idle alone is noticeable

 

[3rdMarDiv]

Re: overheating 91 70hp issue

Harbor Freight non-contact temp gauge 20 bucks...:joyous:

 

[fishfeatures]

Re: overheating 91 70hp issue

thanks great, just a shame the nearest store is a couple of thousand miles away :laugh:

i have enquired about this one though earlier,
guess it'll be another tool that i'll come in useful.. Think i have sourced a spare head just to rule that out too, i'll pick it up tomorrow and swop around everything an see how it runs.

www.ebay.ie/itm/New-LCD-Digital-IR-..._Measurement_Equipment_ET&hash=item19d447a740

 

[pn]

Re: overheating 91 70hp issue

is the pee hole water hot? steaming? you should be able to put your hand on the head for about 2-5 sec without it being uncomfortable. 130-160. take a peek though your spark plug hole for wash out. is anything elese non wp related acting funny.
i always thought the head temp sensor worked by making a ground goround out wire and it should sound. resistance/ohms should go down by temp increasing.

 

[fishfeatures]

Re: overheating 91 70hp issue

i always thought the head temp sensor worked by making a ground goround out wire and it should sound. resistance/ohms should go down by temp increasing.

I think a have a bad meter... i took out the sensor and placed it a pan of water on the cooker and with another meter it gives continuity when the water is boiling, so it does close or ground out. So i can rule out the sensor yes ??

Also with the pressure gauge in aoperation, there is no tell tale as all the water gets diverted to the gauge to give a true reading. What i am thinking of doing is this, if i tap the gauge into the lower part of the exhaust housing where the original tell tale was and run a tube from the mod at the top of the block to the pisser then this should still give a true gauge reading and pisser will then work too. yes ?

I can put my hand on the head for 3-4 secs

Whats a wash out ?? if you mean water getting into the cylinders then i don't think so as it's not missing and i haven't lost even 1 mph from what it always ran at.. it idles fine too.

 

[pn]

Re: overheating 91 70hp issue

well if you can put your hand on the head for 4 sec. and it's not hot and the pee stream isnt' scorching then i'd start lookign for a short or. maybe your alarm is telling you something else, low oil, etc. i think my pressure line is tied into my pisser line i stilll get a good reading

 

[patrick4266]

Re: overheating 91 70hp issue

I have that exact same motor, mine also overheated. There is a service bulletin that tells you how to reroute the tell tale to the top of your head. That will fix it.

 

[fishfeatures]

Re: overheating 91 70hp issue

well if you can put your hand on the head for 4 sec. and it's not hot and the pee stream isnt' scorching then i'd start lookign for a short or. maybe your alarm is telling you something else, low oil, etc. i think my pressure line is tied into my pisser line i stilll get a good reading

vro is disconnected so don't think it can be anything but an overheat situation but i'll try the new head and see if it sorts it first , if not then i'll wait to get a tem gun and check the head when alarm goes off.

 

[fishfeatures]

Re: overheating 91 70hp issue

I have that exact same motor, mine also overheated. There is a service bulletin that tells you how to reroute the tell tale to the top of your head. That will fix it.

already been done mate.

 

[Will Bark]

Re: overheating 91 70hp issue

Just for giggles disconnect the tan wire at the sensor when it's sounding and see if it shuts up. If it does and it's not actually in overheat then you have a sensor going south on you.
good luck

 

[fishfeatures]

Re: overheating 91 70hp issue

Just for giggles disconnect the tan wire at the sensor when it's sounding and see if it shuts up. If it does and it's not actually in overheat then you have a sensor going south on you.
good luck

if it happens tomorrow, i'll def try that , but with that wire pulled then there is nothing to send the powerpack into SLOW is there??

 

[Will Bark]

Re: overheating 91 70hp issue

You didn't say anything about it going into SLOW but isn't that what the other wire is for?

 

[fishfeatures]

Re: overheating 91 70hp issue

You didn't say anything about it going into SLOW but isn't that what the other wire is for?

All i'm saying is that doesn't the wire from the sensor grounding out trigger the pack to go into SLOW?

I don't want an overheat alarm to go off , then pull the wire at the sensor, and keep the motor at 1/2 to 3/4 throttle for another little while to see how it runs. Surely doing that will cause more harm than good??

 

[Will Bark]

Re: overheating 91 70hp issue

On post #5 you say you are holding your hand on for 3-4 seconds; if you can then I don't see how you can be in overheat, I may be wrong. Try putting drops of water on top of the block when its running and see if the water boils or just sits there; if it just sits there you are not in overheat. I've watched two really good OMC mechanics do this. Good luck

 

[fishfeatures]

Re: overheating 91 70hp issue

I think i have a dodgy sensor , same story again, and the sensor is the only thing that hasn't been changed. Good pressure, no vro btw, new stat, different head and after switching the ignition on and off 4-5 times after stopping the motor at the shore the alarm ceased sounding. Head was hot but could do 3 sec test ..

 

[Will Bark]

Re: overheating 91 70hp issue

Joe Reeves nor F-R has chimed in but I remember one of them talking about a flaky alarm horn that could go nuts and I think they were referencing a 70 hp engine. Maybe they will see this and chime in for you. Hope they do. Did you try the water drop method yet?