[justpassinthru2]

Hi all,
I have read in past posts some guys having problems and poston her for advice. I have responded to a few with my novice experiences and hopefully help someone out. Now I find the need to post a problem of my own. Here goes.........

Before dunkin the boat this year, in the startup the engine process, I found my starbord head reaching temps of around 160 and the port head normal. I figured it was a stuck thermostat so I gave the housing a few raps with the hammer which seemed to free it up. In the water, the port head runs about 130 degrees at idle and drops down to around 100 to 125 degrees at 4000 rpm. (I beleive this is normal) The starbord head was the exact opposite! (100 to 125 at idle and about 135 at 4000 rpm. A few nights ago, the temp rose to about 145-150 at 4000 and I beleive it would have gone higher if I didn't throttle back to 1500 to let it cool down a bit. Yesterday I replaced the thermostat, it's round collard seal, the big round pop-off and it's associated white plastic pieces (inner centering plastic piece was melted from a previous overheat) and the housing cover gasket. Used a light coat of silicone on both sides of the gasket being carefull not to cover the water passages. I fired up the engine and let it warm up and now the starbord head creaps up to about 140 and stays there at idle. A test drive produced a temp of 145 - 150 at 4000 rpm and stayed there.

I am a bit confused why my symptom actually got worse and am seeking opinions. I am familliar with the water jacket diverters because years back one came dislodged in my port head and I replaced them all in that head. My symptom then was different, temp just kept rising untill the overheat buzzer sounded. This is when I installed the independent temp sensors sharing a gauge on a single pole double throw switch. My water pump seems to be ok because I have good water flow and the port head is cooling fine. I am patiently waiting for your much valued responses before I move forward with this issue. Could there be a restriction under the exhause cover????? I hope to God not because I tried loosining one of those bolts one day and snapped it off. Thanks in advance for all those who contribute to the solving of this problem. Feel free to PM me if you would like.

Ray

 

[woodc12603]

Normal temp range?

I think the normal opening temp for those stats is about 140-145. You may need to replace the other one which is running colder. I suggest you check the specs for the motor. Running the motor at the proper "warm" temp is prefered to running it cold I think. My 1993 90hp Evinrude uses 145 degree thermostats and is spec'd to run at about 160 when warm.

 

[Bigkeepers]

I agree, those temps may not be too unusual for your motor. I know with my Yamaha the overheat buzzer triggers around 190 and shuts off at like 175. You can give it the two finger test. When the motor is warmed up, hold your first two fingers on the cylinder head cover next to where the plugs are. If you can count to two without burning your fingers, its not overheating. If you have to pull away real quick, its too hot, seriously I'm not pulling your leg.

Also you said the water pump is fine because you seem to get good pressure and one side is cooler. How long has it been since you changed it? I know these things are "made to last a few seasons" but for the $50 or so it costs for the kit, why not have the piece of mind knowing your impeller is new each spring? Plus its easier to get that gear case off if the bolts come out each spring.

Just my .02 of course.

 

[justpassinthru2]

UPDATE 1977 150 hp Johnson Running Hot?????

Today I replaced the port stat, seat & gasket. All else looked like new. Probably cause I changed it last year. At idle for about 20 minutes, no change on the gauges....they looked the same as they did b 4 I changed the port stat. Today I remembered 2 bring my infrared gun and shot all 6 cylinders in the same 12 places. All numbers showed a range between 135 & 146.....coolest on the top. Head to head the numbers were at the most 3 degrees different. In conclusion, the port side temp sending unit is reading cooler than it should by about 20 degrees. Once I replace that sending unit, all should read correctly. Did not take it out to run at full throttle yet. I will do that in a couple days after I replace the sending unit and report back. These stats are rated at 143 degrees so there is not much head room b 4 overheating. Maybe I should hook back up the buzzers just incase.

Shouldn't this motor cool down a bit from the idleing temp once you hit the higher RPM's??????

 

[woodc12603]

Sounds like you have a good handle on things, what about pressure relief?

I don't have spec's back to 1977. 1992 is my earliest and the 150 was a 60 degree looped charge engine then. I assume that you have a 90 degree cross flow V-6 motor. My '93 90hp is a 90 degree cross flow V-4 and its high end temp spec with 145 degree thermostats is 160. The temp of a warm engine run at full throttle may be slightly more or slightly less then the idle temp, but I would expect it to be at least equal to the thermostat temp of 145 and no higher than 160. Is the pressure relief system on your motor a spring that the thrmostat sits on or is it separate?

 

[justpassinthru2]

Pressure Releif System.....

The pressure releif system is a kinda large spring that presses against the thermostat housing and the releif rubber seal just below the stat itself, so I would say it is seperate....all in the same housing though. Why do u ask????

 

[1ReelDeal]

old piggy back

Had a similar motor on my last boat. Ran like a champ forever. An oldtimer once told me that even though the water pump is pumping and seems to be working fine, a new impella seal and housing (rebuild kit)will do wonders to increase the effeciency!

 

[woodc12603]

justpassinthru2 wrote:
The pressure releif system is a kinda large spring that presses against the thermostat housing and the releif rubber seal just below the stat itself, so I would say it is seperate....all in the same housing though. Why do u ask????

Just thinking that if the spring deformed it could interfere with the thermostat, preventing it from opening fully. I would say that you have covered everything but the water pump and scale on the walls of the jacket. Maybe when you change out the sender you will find that things are working as they should. Good luck.

 

[justpassinthru2]

UPDATE 1977 150 hp Johnson Running Hot?????

Swapped out the sender and at idle bothe heads are at 145. While underway, the port head cools down to about 130 while the starboard head remails at 145 or climbs up to about 150 to 155. Any thoughts on why the difference now???? Thanks to everyone for their help on this!!!
Ray

 

[Fishbust]

Temps...

justpassinthru2 wrote:
Swapped out the sender and at idle bothe heads are at 145. While underway, the port head cools down to about 130 while the starboard head remails at 145 or climbs up to about 150 to 155. Any thoughts on why the difference now???? Thanks to everyone for their help on this!!!
Ray

Yeah I agree it sounds like you are really on top of things.

Only things that come to mind is I feel there is nothing wrong with your motor other than its age....it is completely NORMAL for 2 stroke outboards to see 150/155 idling in a hot creek for too long, which may not be long at all. The cooling systems are not efficient at idle speeds and I feel your 20 minute idle testing times are too long. Also, with some designs, in the absence of a crossover hose from head to head, one motor will get more fresh water first, enabling it to run slightly cooler. I do agree 20 degrees differential is a bit much but it is a very old motor, so you could have some buildup effecting heat transfer. Your bottom exhaust ports are large, I would not expect a restriction there. If there is buildup, I would expect to see it in lower water flow areas in the water jacket in the heads. The only problem with pulling exhaust side covers and head covers to inspect and clean is what you already experienced .... snapped off bolts. Not fun, I have been through that on motors 10 years newer than yours, so there was not much you could have done to prevent this from happening.

Overall though, I would tend to trust a temp head shot with your gun better after a proper (short) warmup to 145 and a run out and back at normal cruise where cooling water flow has been right, a better fuel mixture/better air flow. I think this would be a better test for what is supposed to be going on, rather than sitting there idling and shooting the head with the gun over and over, getting more and more paranoid with each higher reading.

 

[Brenainn]

Fishbust

Great advice again, congrats and thanks on 1000 intelligent posts!

 

[Bigkeepers]

This is a shot in the dark but, if he has a V6 with double barrel carbs and the starboard side of the carbs happen to have a little bit of varnish and gunk going on causing the starboard bank to run a bit lean he would be seeing an increase in engine temps perhaps.

Lean running two strokes will run hot and if left that way eventually commit suicide.

Also as much as I hate to say it, if the exhaust manifold area has never been cleaned out with new gaskets and stuff it could cause uneven temps as well. I know those bolts are bound to snap and there are probably about 25 of them but it is another place to consider. One thing I was taught is that when a customer complains about overheating or hotter than normal temps and you've exhausted all possibilities (impeller, stats, etc) the exhaust chamber between cylinder banks is the next place you should look.

I'm having overheating issues with my Yamaha and right now I'm looking everywhere but the exhaust part. I'm trusting that the marina who serviced my lower unit put the new impeller kit in properly and did not forget the woodruff key but I am going to check that today before I take apart the starboard cylinder heads and jacket covers. I did the port side and did not find any major blockage. Both of my banks are overheating at the same rate to the same temps. The bolts I took out looked brand new and luckily did not snap. They also did not seem to be torqued on any longer. They were real easy to get out. Probably because the gaskets were original from 1987 and had never been changed before.

 

[highhook]

Wow 1977 still running, that's pretty amazing.