Running hot... high RPM

[84Ranger]

I have a 1984 Mercury Black max V6 150....
The problem I'm having is I'm getting an over heating alarm at high rpm and wot and if I'm under 30mph I can ride all day without the overheating alarm coming on...but once I get it pass 30mph and within a minute the over heating alarm sound off and I have to back of the throttle and it will go off......I change out the impeller and gaskets and still have the same problem. I remove the T- stat housing and found that there is no t-stat in it and is gone.....but I been running like that for over 3 years now without any problems at all until now....didn't know I didn't have any t-stat....got to get some now....could it be the problem or not. the water seem to be coming out ok from the tale tale..........I don't know but where is the Poppet valve on my motor....could it be that and if it is or seem to be it.... where is it located on the motor? I back flush out the motor and the water seem to flow through ok without any restriction. I inspected the spark plugs and is ok ........I haven't done an compression test but will do that too...........any ideas what could be the problem of my over heating situation......any suggestion is ok.....thanks.

 

[j_martin]

Re: Running hot... high RPM

Stats are needed to warm it up so you don't cold freeze it right away. When you put them in, the telltale will not go much at all until the engine is warmed up, usually in about a minute. That's normal.

The poppit is on the starboard side, near the bottom of the motor, just above the exhaust plate. It's easy to take out and inspect. Any crud there, or in the drain hole that goes downward from there into the exhaust plate will cause it to overheat.

Have you ever wiped out a water pump where there were pieces of the impeller missing. If so, they are probably lodged in small passages, well guided by Murphey's law.

It would help a whole lot if you had a pressure gauge on it and could report what the pressure is at various rpm's.

I ran over a rotton log once, barely felt it, but I took covers off and picked toothpicks out of the cooling system for about a month before it got right.

hope it helps
John

 

[84Ranger]

Re: Running hot... high RPM

Well I haven't wipe out an impellers yet..... took it out again today to see what I can find and drove bout a minute from the launch at WOT and the over heating alarm went off again.... the water pressure at 15psi when it went off and bout 4,000 rpm or so. But at one point the motor did run ok without any alarm at all and it ran ok for 10min at WOT until I stop.....could there be something clog somewhere?...but i notice that the motor ran alot lounder when the over heating alarm didn't come on at all and ran ok......than when the motor sound a alittle quite and feels like a slight loss of power that when the over heat alarm comes on shorty after WOT...but when the motor sound loud the over heating alarm does not come on....and feels like it has more power.......hard to explain...gosh!!!!!!! I hope yall understand what Im trying to say......cloud it be clog carb or uneven oil and fuel mix (haven't change the way I mix 50:1), or restriction somewhere.....but I will check the poppit valve.....thanks again

 

[j_martin]

Re: Running hot... high RPM

I understand what you're trying to say.
Running lean can overheat the engine, and is likely to cause much more serious damage. I believe you have a restriction in your fuel system that is causing it to run lean. Thank the Lord you have a touchy temp sensor.

I have fought this before, and I think about everything that could be wrong was in my XR4. What I found was:
1: An almost invisible white gel formed in the gas tank, probably from bacterial action on on water, or phase seperated alky-fuel.
2. This repeatedly plugged the fuel filter.
3. The carbs were off a little. Rebuilt them.
4. Valves bad in the fuel pump.
5. When I rebuilt it, I put a nice new soft line on the impulse port of the pump. It caused a loss of performance.
6. The Little finger sized fuel filter kept plugging, I chit canned it an put in a Racor 60 GPH water seperating filter.
7. The Atwood replacement fuel line and primer bulb wasn't up to the job.
8. The last thing I replaced, which completed the fix, was the plastic aftermarket bayonet fuel fitting in the motor.

I shot the bug out with a temporary remote fuel pressure gauge. Each item improved things. #8 took it to "good to go".

hope it helps
John

 

[oldrock]

Re: Running hot... high RPM

John, great post! I am having the same problem with my 2001 merc 50hp 2 stroke. It runs beautifully at idle and revs very smoothly. If I keep rpms to about 4000rpms and don't trim motor up too much, I can run all day long with no alarm. However, if I trim it up too much and/or get the motor up over 5000rpms, alarm will sound after a couple minutes.

I changed the impellor out on mine and have good strong steam out of indicator but alarm still sounds if I rev it over 5k. Maybe I should try doing number 8 and see if that happens to fix it.

 

[84Ranger]

Re: Running hot... high RPM

Thanks.....I'll try all that is listed and see how it goes.......order my fuel pump kit and carb kit......and will be checking all my fuel lines and tank for any restriction or anything that will clog that fuel flow....thanks again.

 

[DuckOfDeath]

Re: Running hot... high RPM

I had the same symptom and found the telltale hose was partially obstructed. It seemed to have good flow so I never suspected it until I had it removed and tried to blow through it.

 

[j_martin]

Re: Running hot... high RPM

I had the same symptom and found the telltale hose was partially obstructed. It seemed to have good flow so I never suspected it until I had it removed and tried to blow through it.

These are V6 engines. There isn't enough water going (or not) through the telltale to make any difference in the temp of the engine.

John

 

[DuckOfDeath]

Re: Running hot... high RPM

Ahhhh. good to know - thanks for correcting me.

 

[84Ranger]

Re: Running hot... high RPM

Ok....I remove all the carbs and inspect all three carb and is ok. Installed all new gasket and inspect all fuel hoses and is all ok with out any restriction...lower the the motor into a water tank and it took a long time to start...had to spray starting fluid into the carb to get it to start...but once it started it started ok everytime...guess it just needed some fuel to kick start the motor.....but once the motor started it took a long time for the water to come out the pee hole....forgot to note that last time...for some reason sometime the water will come right out the pee hole when the motor is started and sometime it will take a long time before there is any water coming out of the pee hole....once the motor start it took bout almost 60sec for the water to come out....turn off the motor to check everything out......about 5min....and restart the motor and there was no water coming of the pee hole at all and smoke start to come out of the pee hole so I turn off the motor asap....I suspect the water pump and impeller but I just installed a new impeller....so I remove the lower unit and remove the water pump housing and found that it melted on the top of the housing where the shaft goes through and the impeller was stuck to the housing.....once I remove the housing I found the gasket between the house and base was missing a pice of the gasket....could this be the problem of my over heating problem.....Im getting a water pump kit and will be installing it in..........thank's again