Honda BF25A leaking oil when hot.

[Bobbywolf]

When running under load for awhile, then shutting down, and tilting the motor up, oil was seen leaking from the lower cowl weep holes. Looking inside the hood, there is no obvious source of the oil, so I'm thinking powerhead base gasket. See pictures.


I didn't think the motor was getting hot because no alarm sounded, and the indicator stayed off.

I have since pulled the thermostat and verified it opened with hot water. I pulled the temp sensor switch and verified it shows continuity when heating it in oil as per the shop manual, and the alarm sounds in the boat. Both good.

I finally went into the water pump and found it trashed again (it was replaced this past spring). It was still pumping out the tell tail, so I didn't immediatly go here.


Do you think it is worth pulling the powerhead and oil pan to replace the gaskets since they may be comprimised now?

EDIT: Also, when the 1st impeller was replaced, there was VERY little left of it. What are the chances of this debris blocking up the water passages, contributing to the overheat?
(1998 Honda BF25A 4stroke used mostly in salt water)

Thanks for any thoughts.
Rob

 

[MattFL]

It's not normal for impellers to come apart like that under normal use. Was that an OEM impeller, or after market? Also did you replace the cup at the same time? Was the motor ever run out of the water? Or maybe run through a lot of sand? The top edges don't look melted so maybe it wasn't running dry that killed it, hard to say. When we first switched to a 4-stroke years ago, my brother forgot to turn it off after we pulled the boat out of the water and it ran for a couple of minutes before we noticed. No harm to the motor, but some of the plastic under the wear plate melted. Still the impeller didn't come apart, so that's got my wondering what's going on with yours..

It is possible bits of the impeller are blocking things, but I don't think that would contribute to the current impeller coming apart, and the current impeller doesn't look capable of pumping enough water IMHO.

I'll let someone more familiar with that motor respond about what the leak might be, but definitely fix the leak.

 

[Bobbywolf]

It's not normal for impellers to come apart like that under normal use. Was that an OEM impeller, or after market? Also did you replace the cup at the same time? Was the motor ever run out of the water? Or maybe run through a lot of sand? The top edges don't look melted so maybe it wasn't running dry that killed it, hard to say. When we first switched to a 4-stroke years ago, my brother forgot to turn it off after we pulled the boat out of the water and it ran for a couple of minutes before we noticed. No harm to the motor, but some of the plastic under the wear plate melted. Still the impeller didn't come apart, so that's got my wondering what's going on with yours..

It is possible bits of the impeller are blocking things, but I don't think that would contribute to the current impeller coming apart, and the current impeller doesn't look capable of pumping enough water IMHO.

I'll let someone more familiar with that motor respond about what the leak might be, but definitely fix the leak.

The replacement was a OEM Honda kit. The outboard was run for an extended time on muffs while troubleshooting the oil leak/overheating issue. I just read that these are not very good at running on muffs because of the 3rd water intake (that I just learned about) by the trim fin. I am willing to conceded this 2nd impeller failure is due to lack of water, but truly if that were the case, I would expect things to be more melted than broken as they are.

The motor is off the boat and on a stand. I've resigned myself to pulling the powerhead regardless, because I cannot rule out a blockage causing the inital overheat, and I'd feel better with new gaskets in there.

Rob

 

[flashback]

I have an old BF 75 on a sailboat and a mud dauber type bug stopped up the crankcase breather hose which caused the engine to leak oil past the main oil seal under the flywheel..

 

[Bobbywolf]

Well, I have the gaskets on order so I started to take this thing apart. I got the extension case off to expose the oil pan. I removed the exhaust pipe and water tube and all 8 bolts holding on the pan. It was fairly corroded in place but some whacks with a rubber mallet and it popped free.... almost.

The pan only drops about 1/8" at best. It feels free, is able to turn a few degrees either direction, and move up and down the 1/8". The service manual shows nothing more to remove. It is almost like it is hanging up on the oil pump or pickup. It comes up hard. Hell I've even stuck a borescope up the oil drain and I cannot see what is hanging it up.

At this point I've hammered and pried a little more than I should have, so I'll take a break from it for a day for ideas. What is the trick to this blasted thing?

Rob

 

[MattFL]

I can't help with disassembly, but muffs are fine if it's getting enough water. My 50 has the same water vent over the prop and I've been flushing it on muffs since I bought it new in 99', I let it run at high idle (~1200-1500rpm) for about 15 minutes while we wash the rest of the boat after every use. Just make sure there is enough water flow that a lot of water is coming out that water vent. If it had a good pee stream while on the muffs then the problem wasn't lack of water. I wonder if you got a counterfeit impeller, or super old inventory that had become brittle?

 

[ahicks]

Bobby if this motor is anything like it's bigger brother 35-50 hp (that I know like the back of my hand), there's a bolt holding the oil pan that's very difficult to see, located between the exhaust port and the oil pan. In any case, you can pull up a parts diagram and verify where nearly every one of the bolts is located.

I smoked a few of those impellers learning you can't run them on a set of muffs unless you have VERY good water flow - AND - never run it over an idle! I cut down a trash can so I wouldn't have to worry about it when messing with them.

As far as your oil leak, if that were a 50, my bet would be the valve cover gasket....

 

[Bobbywolf]

Bobby if this motor is anything like it's bigger brother 35-50 hp (that I know like the back of my hand), there's a bolt holding the oil pan that's very difficult to see, located between the exhaust port and the oil pan. In any case, you can pull up a parts diagram and verify where nearly every one of the bolts is located.

I smoked a few of those impellers learning you can't run them on a set of muffs unless you have VERY good water flow - AND - never run it over an idle! I cut down a trash can so I wouldn't have to worry about it when messing with them.

As far as your oil leak, if that were a 50, my bet would be the valve cover gasket....

Well... you were right. I actually found em before I read your message. These 2 little devils were causing all my grief!




Revisiting the manual, it does indeed say 10 bolts. I should have looked a little harder before getting mallet happy. The result is 2 bent bolts. I cannot believe I didnt tear the threads out of the block. The two bolts were backed out about 1/8" just from me wiggling banging and what not. I'll need to find a good straightedge to ensure I didnt warp the oil pan. I very well could have. Such is the cost of DIY sometimes, lol.

I am quite sure it wasn't the valve cover. During my troubleshooting everything was cleaned very well with brake cleaner, and I seen no sign of a leak aside from what was slowly accumulating in the pan from seemingly nowhere.

I'm pretty deep now, the powerhead comes off next lol. It'll be a few more days for an update.

 

[ahicks]

The first one is a tuffy, they're far easier to work on as you get to know them. I found those bolts just like you did - after clobbering the oil pan with a rubber mallet for 10 minutes...

One tip I can share when pulling the power head is I don't disconnect any of the wires. They're all unbolted, and accessories hung over the side out of the way. The starter for instance, is unbolted with wires left intact. That whole gob of wires inside that housing is all left in place, while just unbolting that plastic part. Ignition and charge coils the same way, along with all of the ground wires. You'll find this saves a GOB of time on reassembly..... You just need to be careful of all that stuff hanging over the side - not hard if you are paying any attention at all. -Al

 

[Bobbywolf]

Update time. Powerhead came off without a hitch. Nothing looked amiss with the gasket (metal gasket btw), or the mating surfaces. While hanging I fished around the water passages and found no blockages. Air blows through the block freely as well. The oil pan had a very slight bow in it from the removal process, but it was easily flattened by lapping the mating surface on a machined plate.

On reassembly, I followed the honda service manual for torques and whatnot.

When I finally got to the waterpump, I clued into something I should have earlier. It was assembled wrong. I even posted a picture a few responses ago lol.



That gasket should not be there. There should be no gasket between that plate and the housing containing the impeller. Just the housing o-ring. You can tell it was leaking water since install, and is likely the source of the overheating. If one were to use that particular gasket, it actually belongs under the lower waterpump housing.

Doh.

I'm now expecting this issue to be fixed. Just waiting on a mild day for a long barrel run.