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overheating 90 Honda Marine

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fishphart

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Hello all, I am new to this forum but found it because I need some HELP!! I purchased a aluminum fishing boat with a 90 hp Honda outboard and a 9.9 outboard. Shortly after I began using the boat the motor overheated and scared the crap out of us (my wife and I) when the engine shut down and the buzzer was sounding. My wife was driving at WOT so I just figured it was too much. The engine cooled quickly and we had no further problems that day. However, since then we have had nothing but problems. I took the boat to a authorized Honda repair shop in Reno and was told it must be the pump which I figured. Anyway, the mechanic replaced the pump and the bucket the pump sits in and the thermostat. We still have the same issue but now we can only go about a mile or so before it overheats. We can troll all day with no issues. The overheating occurs at any RPM from 3500 to 4500 or more. I try not to exceed 4500.
Any help at all would be greatly appreciated. My name is Roger
 
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You did not say if your motor is fuel injected or carburated...

If it is fuel injected, the engine has two thermostats and maybe he did not replace them both.

If it is carburated, when he changed the thermostat, did the tech mention that there was any build up inside the thermostat housing? If it is used in salt water, the motor may not have been flushed properly and there may be salt build up. If it is used in fresh water, it still could have a lime buildup inside the cooling passages. A peek into the thermostat housing should tell the story.

The other area on the carbureted engine is the bypass relief valve may be gunked up and sticking. It normally opens up and dumps extra water when the motor is run at high speeds. If stuck, it does not dump. See part 4 that closes down on part 8 with the help of spring part 5.... http://www.boats.net/parts/search/Honda/Outboard Engine/2001/BF90A1 LRTA/THERMOSTAT/parts.html

The best thing to do, unless you are pursuing this yourself, is to take it back to the dealer and have them take it onto the water to see first hand or at least take it out after they do more testing to make sure that they found the problem.

Sometimes, this kind of problem is not that straightforward and takes a few tries to get the problem solved.

Mike
 
Hi Mike, your help with this is invaluable to me, thank you. I removed the thermostat housing and thermostat (new two months ago) and checked for any blockage. I tested the thermostat and it opened at 170 degrees as it should. I removed the bypass relief valve and the same, no blockages. As a side note, how does that thing work? Is the spring bi-metal? Anyway, I flushed down through the thermostat housing and the bypass holes but not much of anything came out, just the water. This thing has me baffled and now my wife wants me to sell the boat that we just bought this year because she doesn't trust it and I don't blame her. We boat on a large lake that is known for sudden rough water (3-4 foot) waves and high desert winds. Your boat has to be dependable. But enough of that, do you have any more ideas? I am going to the dealer later this morning to chat with the mechanic. By the way, it is carbureted.
Roger
 
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You just have to have mechanic check to make sure it is actually overheating. Could just be a bad sensor.

I assume when you get the alarm, that the green light is on and the red light has come on....

As I said before, it is probably good to have mechanic take it out then actually see it fail.

The bypass is opened from the exhaust pressure when it is throttled up.

Mike
 
Can you get your hands on a contactless temperature gun? I got mine off ebay for under $20 and it makes checking engine temperature very easy. Best to be sure you are actually overheating before continuing to head down that path for troubleshooting like the dude said.
 
Hi all, yes it is actually overheating. When the alarm comes on, steam is blowing out of the water outlet. It cools almost instantly once pulled back into neutral. I spoke with the Honda mechanic and I told him all I had done to checks things out. I told him when I squirt a garden hose into the opening where the thermostat is located, the engine will with water and spill back out. Some comes out the bottom from the inlet and prop. I feel it should not back up and that somewhere from the inlet to the thermostat, the waterway is partially plugged. Any thoughts?
 
Does this only occur when youre making way or does it happen in neutral as well if you rev up? I wonder if your leg is in clear water when you are planing or if the hull is causing turbulence or some how allowing air under the cav plate preventing enough water getting to the water pump intakes. To check the lower section water passages Drop the leg and clean out the water pump, water pipe and all associated water passages, check that the rubber grommets are in good condition. While the leg is off you can blast water/compressed air through the thermostat housing. I think there are 2 relief valves to check for corrosion on the powerhead and then you are looking at taking off the exhaust cover to check for corrosion there too. Be very careful not to break off any bolts as they get stuck, this will make your problem much more difficult to repair. You will probably want new gaskets if you are going to this length.
 
Ditto to what skronkman said...

You said that the water pump was changed.....if pieces were missing from the old impeller, they may be caught up in the water tube...somewhat blocking the flow. If the mechanic did not backflush, they may still be there.

I always try to reconstruct the old impeller if it is in pieces to assure that we got all of the missing parts.

Before you take too many other things apart, you can remove the thermostat and leave the cover off. Start the engine and see if water dibbles out or has a good flow out. If it dribbles or has a really weak flow, it is time to pull the leg.

If you pull the leg, definitely use a garden hose with a lot of pressure. Water should have a good flow out of the water tube. If you put your finger over the water pickup tube (yes you will get wet), water should also eventually flow out of the telltail indicator.

All that being said.....if the boat has been used in the desert area, like you said, and you said that the waves pick up quickly (possibly from a shallow lake), the motor may have been used in the shallows or beached and it picked up sand or debris. There is a possibility that the debris ended up in the block around part of the cylinders. That would mean, the head would have to come off. But consider this worst case.

The path of the cooling water goes up the water tube to the base of the block. That is where the telltale picks up the water, then the water goes around the cylinders up to the thermostat.

Mike
 
Hi Mike and Skronkman, I believe you have identified the problem and I agree there must be a blockage in the water port from the water to the thermostat but you have raised a very interesting issue about the motor water pickup possibly being out of the water at speed. However, I'm not so sure this is the issue because the first time it happened, we had driven the boat at speed about 20 miles (across the lake and half way back). I do not exceed 4500 RPM and try to keep it around 4000 RPM. Each time we take it out, it gets worse, now we can only go about a half mile before it happens. The mechanic handed the water pump impeller and case to me and there were no missing ends of the impeller. In fact, I thought it looked good but the work was done and I figured that would take care of the issue. I will try removing the thermostat and try flushing it that way to see if the water comes out hard or at a dribble. You guys are a great help to me, I thank you, Roger
 
Is your cavitation plate at level or slightly lower than the bottom of your hull? It should be. Is the bottom of your hull a clean unobstructed path for the water to pass under and exit onto the prop, nothing sticking down or broken off? Is your hull a recognised design or brand? Not a one off?

It is sounding like you are headed in the right direction by looking for a water passage blockage but double checking the above things is fairly easy and they have caused overheat issue in the past. I have seen a sort of aluminium end cap that covers the bottom of the transom and the V in the hull, only about an inch in all directions that came loose and protruded down under the hull an extra 3/4 of an inch after a boat was accidentally dropped off the trailer onto the ramp. It created turbulent water at speed to the prop and started overheating the engine.
 
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