1986 100hp crossflow cooling question

[horiconducker]

First off sorry about the long post,Last year I bought a new to me boat with twin 1986 100hp crossflows. I replaced water pumps, water deflectors and put new thermostat kits in it to cover all bases and be problem free. Ran it a few times through the summer no problems. Came time for duck hunting in november (30 deg F)started having and idle overheat. I would start it up let it warm up awhile, atleast five minutes and buzzer would go off and i would shut it down immediatly. I always carry my infared temp gun and sure enough starboard side was around 200F, port side was 130ish. Let motor cool down to 140 degress and refired and temperature would climb to about 170 and ,then the thermostat would open and temp would go down to 130ish and be fine the rest of the day, i would let it idle for 30mins and monitored temp and it was fine. I had this happen 3 or 4 occasions, start up, overheat, cool down, restart, temp would climb but not high enough to set the buzzer off, then thermostat would open and would be fine the rest of the day. It was always only the starboard bank on my starboard motor that would overheat.

 

[horiconducker]

Re: 1986 100hp crossflow cooling question

In fall i read on here about some other having same sort of problem from not getting enough flow through those 2 pins holes in the thermostat housing. Well this spring i pulled thermostat housing apart put a new thermostat kit in and and drilled open those two little holes in that spacer plate. If my memory serves me correct i meausured those holes to be .060 or so and i think drilled them out to around .090. Well now my problem is that my motor at idle only gets to 90-95 degress on port bank, and 100-110 degress on my starboard bank. Im wondering if i should replace that spacer with the little holes i drilled out, or should i just run it the way it is, just dont want to do any damage buy running it too cold especially since i will be using it primaryily in cold air temps, 10f- 30f, but i also dont want to keep overheating it either. Again sorry for the long post, any info will be greatly appreciated. thanks ducker.

 

[emdsapmgr]

Re: 1986 100hp crossflow cooling question

I'd replace that starboard stat (probably do both at the same time.) You are correct that those two small holes in the valve body need to be open to have proper cooling at idle. If they plug up, the engine will overheat at idle. The fact that you drilled them out may or may not be a problem. If you are running the engine in cold water, it may not be heating up due to the water temps. My engines run cold in the spring and fall due to the water temps, but do warm up normally in the summer. You should see idle temps in the summer around 143-150. If you are concerned, you can replace the valve body in the stat housing. Some of the new/replacement valve bodies have just one oval hole-an improved version. The hot horn should come on around 212 degrees and will silence when the engine gets back down to 175. When running on plane, the pressure relief valves open, flooding the powerhead with cooling water, greatly decreasing the cyl head temps. Check your horn itself. My 1992 horn gives me a constant horn (hot horn) just when the oil tank is low-not the correct signal.

 

[SparkieBoat]

Re: 1986 100hp crossflow cooling question

also you will not damage your motor by running it too cold, worst case is poor fuel milage..I would run it and see what temps you get out on the water. probably be fine..also be sure your water pump impeller is good and replace it if it is over 3 years old.

 

[horiconducker]

Re: 1986 100hp crossflow cooling question

I did replace both stats in my starboard motor this year again when i drilled out the 2 holes in the valve body. I replaced entire water pump last year too. The first time it overheated last fall I thought the hole in the valve body was plugged and then cleared it self, but when it happend the second and third time in the exact same manner, start, overheat, cool off, restart, start getting hot, and then cool of to normal temp for the rest of the day, i started thinking that not enough hot water was getting to that t-stat initially, which is why i drilled the valve body holes open to allow more water to the stat. As far as the cold water yes it is cold water running on the muffs, but my port engine reaches higher temps, about 120 on port side 130 on starboard side as where my starboard engine only reaches 90-100 on the same hose and muffs. I have test all buzzers to work and even pulled overheat switches out and tested them in hot oil last year so all should be good there. Is it probable, that drilling those valve body holes bigger brought the engine temp down that much? I have no problem replacing it, but i just dont want to get the overheat again. How bad may that coke the rings up, I only put maybe 30hrs a year on the motors, but a good portion of that is at idle speeds? thanks again ducker

 

[SparkieBoat]

Re: 1986 100hp crossflow cooling question

it could have something to do with the deflector. here is a great post with pics that Ezek just gave..look at post #12
http://forums.iboats.com/showthread.php?t=400565

 

[emdsapmgr]

Re: 1986 100hp crossflow cooling question

When that starboard head heats up to 200, what happens if you immediately bring the boat up on plane? The pressure relief valve(s) should open and the head temp should plumment drastically. If so, it would indicate the issue is at idle only. If the head stays hot when on plane, you could have some blockage in the cooling system on that side. Maybe debris inside the starboard cyl head cover....