strange over heating issue

[Rdepaoli1]

I am having the weirdest overheating problem! To start the motor is a 1983 Johnson 200 V6 (j200tlcts) She runs like a gem & starts up very easy for her age. My problem is that every time I run over 4000 RPMs it quickly starts to over heat. But it is not a constant over heat, only at high rpms. I have had her out running for hours, at 3400 doing 22mph & perfect temp. it is only when I cross the 4000 mark it gets hot, and once I slow down it quickly goes back to normal.
This season I have put in a new water pump, thermostats ( teletale runs great & increases with throttle) I change the plugs & fuel filter every two months. Also put new powerpack on starboard side & changed bad regulator & rectifier. Also did a full seafoam decarb. Since the problem started, I have checked compression & it was even across the board. Checked spark on all cylinders & they were all firing. Checked the whole fuel system & cleaned pumps, all was working fine there. Also I noticed that top cylinder bypass cover or inspection port on the starboard side was leaking, so I took it off & saw the piston had no scratches & ring was perfect & noticed that the whole area was immaculate, before I replaced the gasket and fixed the leak. Finally I took out the thermostats & flushed with fresh water & put back together without thermostats & she still is having the problem with NO thermostats? Also it gets up to around 130 degrees when it is warm & stays there till I pass the 4000 threshold despite the fact that she has no thermostats.
From start up you can feel that the water coming out of the starboard exhaust port is noticeable hotter than the port side, & when she over heats I check the head with a digital thermometer & the starboard side reads about ten degrees hotter.
There seems to be a lot of oil in my exhaust, it makes a decent slick when I start & idle, maybe 5 or 6 feet around boat. But I have never had a Johnson before & don?t have a comparison at my marina, so I don?t know if I ?am just paranoid about that. And from time to time I notice she smells like she is running rich at idle but again I don?t know if that is just my head screwing with me. Also I do have some black oil running down my leg. That is the whole story? I don?t know what else to do. She runs fine & strong at 130 degrees with or without thermostats & will go all day. But I can?t go more than 4000 rpms? Also I run a perfect 50;1 on the fuel & run stabil marine on every fill up.
Any help or advice would be greatly appreciated.
THANKS Rich.

 

[dazk14]

Re: strange over heating issue

All that writing and a digital thermometer...could you better describe "Hot"?

 

[Rdepaoli1]

Re: strange over heating issue

normal running temp with out thermo is 120 -130 on port & 125 - 135 on starboard. over heat alarm sounds 150 - 160 on port 160 -170 0n starboard. & once i slow to idle it colls back to running temp in 2 minutes.

 

[fshrgy99]

Re: strange over heating issue

Just a shot in the dark. If the fuel delivery is limited by a failing pump, air leak or blocked fuel filter there will be lots of gas at idle and low rpm, but high demand at WOT would result in a lean condition and a motor that overheats.

 

[Rdepaoli1]

Re: strange over heating issue

thought of that. i replaced all the lines & rebuilt the pump. also i was changing filters like a mad man & even cut one up to see if it was gunked & it was spotless. thanks.

 

[emdsapmgr]

Re: strange over heating issue

You'll get an overheat alarm at 212 degrees. The horn will silence when the powerhead cools to 175. (still too hot for normal running.) It should idle between 143 and 150. When on plane, the pressure relief valves open and the powerhead can cool sometimes as much as 20+ degrees from normal idle temps. If you are getting an overheat when at higher planing speeds (over 4000) rpm's you may have a cooling restriction in the powerhead, slowing the volume of cooling water through the block. Some things to check: 1. Make sure the rubber water diverters are in their specific place between the cylinder liners and the block. One per each cyl. They can get out of place with age and can restrict water flow around the cylinders-causing an overheat at one or more cyls. You will have to pull the heads to check this. 2. Pull the cylinder head covers off both heads. Check for restrictions inside the head coolant passages, such as sand or weeds. Not unusual in engines on fishing boats. Since you are from New York, you may have salt deposits in those passages. 3. Check for any signs of restrictions around those same cyls when you have the heads off-sand, etc. 4. If you find any debris in the powerhead, keep in mind it may also be inside the block between the cylinder banks. Remove the the water passage cover under the flywheel to have a look down the block. 5. If you have oil running down the leg, it may be from the powerhead base gasket. If that base gasket is faulty, it could be out of position-letting exhaust escape into the cowling area. Further, it may be restricting the water flow from the exhaust adapter to the underside of the powerhead. I'm not a fan of running without stats. They restrict the water flowing out of the block to insure that the block is always full of water-to the top of the block. They insure even cooling throughout the powerhead. Sometimes engines can run too cool with no stats, promoting carbon accumulation around the piston rings.

 

[boobie]

Re: strange over heating issue

You could have some swelled up water deflectors in the block under the cyl heads blocking correct water flow.

 

[clanton]

Re: strange over heating issue

Boobie said it. Water deflectors cause high rpms overheat. Seal between the waterpump impeller housing and the impeller cup causes same.

 

[Rdepaoli1]

Re: strange over heating issue

thanks guys. Come to think of it, I did notice last week when I flushed the head out with the hose that water was spraying out of the seam where the lower unit meets the leg, as if the gasket on the waterpump housing was leaking. Also it is weird that my alarm goes off so early, but by it doing so I found that the starboard side alarm is faulty, which is good as that is the hotter side & now i will replace both.

 

[Chinewalker]

Re: strange over heating issue

I am almost certain I know what's going on - I had the exact same symptoms with my 1984 90hp immediately after installing a new waterpump kit.

In the top of the plastic impeller housing there is a small channel that runs through the o-ring groove. This channel MUST be open. I was careless with the sealant when I installed my kit's o-ring, plugging off that channel. It's a vent and if it is closed off, the pump will lose its prime. There is even a service bulletin on this problem as apparently I wasn't the first to have this happen...

 

[Rdepaoli1]

Re: strange over heating issue

well I'am gonna wait till i pull out for the season to check the water pump. I'am just gonna put a whole new kit in. as for my investagation was changing all the fuel / vaccume lines to check that box off of my headache, & found that the fuel line to my center carborator was cracked, actually broke. I changed it & the boat seams to be running slightly smoother Although I have not had the time for a sea trial to see if this is my overheating issue. I will keep you posted, & hope i got it..