90 hp Johnson on party barge overheating

Pontoon Pat · Sep 30, 2003

I have a 1993 90hp Johnson on a 30ft Party Hut Pontoon boat that only seems to overheat at full throttle(4500 rpm). I can run this boat all day long at 3500 to 4000 rpm with no buzzer. With my infared gun I was getting readings anywhere from 190 to 210 on the sides & tops of cylinders. #1 being the hottest. I've changed the thermostats, put in a waterpump kit, and deflectors on the starboard side(1&3){210 degree side}. Now when I run full throttle the buzzer still sounds and my readings are down to 190-195 degrees. My dash gauge reads 20psi since replacing the pump. I'm at a loss. Any ideas out there?

Hooty · Sep 30, 2003

Re: 90 hp Johnson on party barge overheating

Maybe you're just partyin' to hearty, Pat. Can ya give us a little history? Is the rig new to you? When did it start over-heating? Any events (besides partyin') before over-heating? Run over any water lice, stumps, etc? c/6 Hooty

ob · Sep 30, 2003

Re: 90 hp Johnson on party barge overheating

4500 WOT is too low for your 90 hp.I suspect you are lugging the engine and causing it to overheat.Need to prop it where it is capable of 5500 rpm at wot.Higher rpm at wot = less engine load = more water flow from pump. If it was ever capable of running higher than 4500 at wot you may have fouled corburetor issue which can cause a lean condition and lead to overheat.

rickdb1boat · Sep 30, 2003

Re: 90 hp Johnson on party barge overheating

What prop(Pitch) are you running? You would need something like a 14 X 11" to get you in the neighborhood.

Pontoon Pat · Sep 30, 2003

Re: 90 hp Johnson on party barge overheating

I've owned the boat for three years but never ever ran it at wot. I've always felt that it would shorten the life of the motor. My friend was driving one day and decided to open it up and after about 5min the buzzer went off. I've checked compression and have 120 to 122psi in each cylinder. Should I check the timing? We've never hit anything or left the lower unit sit in the down position for any length of time in the river. I believe the pitch is 13 cupped but I'll have to check. Thanks

Solittle · Sep 30, 2003

Re: 90 hp Johnson on party barge overheating

Pat - Don't mess with the timing or carbs until you get the rpms up. You are way over propped. Don't tinker.

rickdb1boat · Sep 30, 2003

Re: 90 hp Johnson on party barge overheating

definitly check the pitch and get yourself a 14 X 11 prop. If need be, it can always be piched even lower to bring the revs up. A 90 HP on that size toon is really pushing the limit. Should be at least a 150 HP for that size. But you really need to get the RPM's up before something bad happens to the engine from lugging. Post any prop numbers you find.

speedwrench · Oct 1, 2003

Re: 90 hp Johnson on party barge overheating

Been there, done that with my 'toon. Wrong prop installed when boat was rigged(gasp). I won't try to tell you what prop, ether borry different ones from friends or get advise from several major manufactures, but get the RPM's up before you do major damage.

Pontoon Pat · Oct 4, 2003

Re: 90 hp Johnson on party barge overheating

New 14x11 pitch prop brings my rpms up to 5100. The bad news is it still overheats. What next? This motor was original oil injected and now uses pre mix. Is there any need to up the high speed jet size for this conversion? The only time I get the buzzer is when I'm in the mid to upper 4's. I can run all day long @4000rpm with 18psi water pressure and no buzzer. Any chance this could be fuel(lubrication)?

rickdb1boat · Oct 4, 2003

Re: 90 hp Johnson on party barge overheating

May be a defective temp sensor. Check it out!

ezeke · Oct 4, 2003

Re: 90 hp Johnson on party barge overheating

I'm willing to bet that if you pull the heads you will find mineral build-up in the cooling circuits. Clean them out and you will solve the problem.

seahorse5 · Oct 4, 2003

Re: 90 hp Johnson on party barge overheating

If your are running in silty, muddy, or salt water, sediment can settle under the cylinder head covers and restrict the outflow of cooling water. Remove the covers and scrape out any buildup there. There is also a possibility of the pressure releif valves sticking in the thermostat housing. If the rubber grommets distort, the white plastic valves may not open up fully to allow the hot water to exit the motor fast enough. If one side is that much hotter than the other at full speed, that may be the culprit.

seahorse5 · Oct 4, 2003

Re: 90 hp Johnson on party barge overheating

Hey, Ezeke, We were on the same wavelength at almost the same time. You posted while I typed the second paragraph.

ezeke · Oct 4, 2003

Re: 90 hp Johnson on party barge overheating

Hi Seahorse, I just can't see how it could be much else if it's running fine all the rest of the time. (Pontoon boat motors never get flushed.)

clanton · Oct 4, 2003

Re: 90 hp Johnson on party barge overheating

I would check the water deflectors in the other side of block. Check that pressure relief valve is not sticking. Temp sensor sets alarm at 203+- 6 degrees F. High speed overheating also caused by o-ring between waterpump housing and impeller cup being out of position.

90 hp Johnson on party barge overheating

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