BF100 Overheating

Yesterday got a BF100 project motor running finally. Picked it up used with supposedly no spark. Found the kill switch was grounded and put a new set of points in and fired right up. Had it in a 55 gal barrel and would idle great, run up and down on throttle and back to idle no issues. Good water from pee hole. I let it run at 1/4 throttle (hood off) for about 10 min. At 4-5 min warm water out pee hole, at 8-9 min hot water from pee hole, and at 10 min the aluminum housing/oil sump was hot. Hot enough that it couldn't be touched. Motor does sound a little loud on the exhaust end like it could have a leak but nothing I could see. The hood hdid have the metal plate that says 4 stroke removed and two 3" diameter holes drilled in its place from the previous owner so I am sure he had overheating issues also and wanted to vent it with the holes.

Besides the thermostat what might be the cause?

I have a bf100 picker up last year.. I believe the pee hole is a bypass. Mine runs cool and I think the thermostat is stuck open.. Harbor freight has a cheap laser temperature sensor you can use to check the heat.. You can get the honda shop manual pretty cheap and it does a pretty comprensive job of describing repairs.. That said, I ruined a good running mercury trying to replace a thermostat when the bolts broke off due to salt water corrosion. Not a lot of torque to do it either. Haven't tried the honda yet since it runs ok.. Biggest problem you may have is getting the bolts loose without breaking them off. Of course if its been running severely overheated then who knows what else is wrong..

Man!...How many "rescue" Honda outboards do you have jduck1? You must be singlehandedly buying up all the old Honda twins within a 200 mile radius! :~)

Anyway, it sound as if it may be overheating for sure....rocknroj makes a good suggestion about having an infrared temp gun...I have two...in two different temp ranges.

I would definitely suspect the stat but it could also be blockage from years of mineral and salt deposits or maybe even something like twigs, grass or leaves....you won't know until you take off the stat housing and have a peek.

Put the stat in a pan with a thermometer and see what it does. I believe they get "sticky" over time and I know that the wax pellet in the the little can on the end of the spring slowly deteriorates (drains out) over time making them unresponsive and inaccurate.

It sounds as if the pump is working ok but I have seen decent pee streams without much cooling because, when I pull the pump housing off, there are only a couple of complete vanes left on the pump impeller. Enough to make some flow to fool you but not enough to efficiently cool the engine.

So, bottom line....on a rescue like this I would pull the stat housing and at least test the stat if not just replace it as CHEAP INSURANCE. I would pull the extension case and make sure that I have a viable water pump. Because for all we know NONE of that has been done in many, many years. And, while the stat housing is opened up, you can backflush the passages with pressured water and maybe compressed air if you are equipped to do so.

Good luck on bringing another one back to the boating "life".

So I pulled the manifold and found the insides to be a little rusty/crusty. Thermostat cleaned up nice and did open fully at 140 deg but have a new one on order so it will be replaced. Cleaned up the manifold and will pull the extension housing off today after work to get the port where the water tube enters the housing.

So I want to blow the ports out from the opposite direction. Do I just use the air nozzle and push air through the water ports and see what comes out? Anything that can be used to help clean out some of the other corrosion or crud that I am sure is in the rest of the motor water ways? Chemicals? Wire pipe cleaner?

Thanks!

Some people swear by SALT AWAY to remove the salt deposits. Vinegar...being acidic... will work to break loose some stuff. I wouldn't go so far as murriatic acid because you may remove something you don't want to....like the oring between block and oil case.

Probing with wire and even string trimmer cord might tell you something but you don't want to break anything off in a passage and have to try to dig that out as well. Anyway, the internal turns the passages make are fairly sharp and getting in "deep" is not a likely probability for a "roto-rooter" type effect.

There are some automotive cooling system cleaners that COULD work but the application is a bit tricky. PRESTONE SUPER RADIATOR CLEANER is very effective at removing deposits and NOT DESTROYING rubberized shaft seals on pumps. But, it requires dosing a system over a fairly long period of time so you would need to mix some in a container with water and then submerge the pump intake and run the engine. Since running an engine in a closed container for any length of time could cause overheating, it would require several "cycles" of run...stop...cool off and then run again. But, that is what I would do if I wanted a really "freshened up" cooling system. I haven't actually done this so this is a speculative DISCLAIMER. I DO NOT KNOW what this cleaner would do to an impeller or to the aforementioned CRITICAL oring between block and oil case. So try this ONLY if you are prepared to deal with any detrimental consequences.

I have this cool little tool that hooks to a water hose and an air hose and it has several sizes of rubber seals that can fit around the tip. It is great for jamming into passages in the stat housing and forming a tight seal. You turn on the water control valve and start pressured water through the passage and then, in short pulsed bursts of the air trigger you "pop" compressed air in there to loosen things up. It is usually wet and messy but VERY effective at getting things that were not coming out with just the water hose. Before I got that, I was using a rag to form a seal. And that works too if you can't find/afford the tool. Also I still have to use a rag or sponge in instances where the tool just won't fit. I'll try and find a link to the tool and post it later.

Here is a link to a very similar tool to the one I have. However, mine is mostly plastic and was about $35. This one on the other hand looks JIMJAM expensive! But, it gives you the idea. And, a "handy" guy could fabricate one from some pieces from a GOOD hardware store. As you can see, an air pressure regulator is used to reduce the shop air to somewhere UNDER 100psi. But I don't think even 120psi would hurt anything in the outboard.

http://www.gates.com/products/autom...ids/professional-tools/power-clean-flush-tool

And...here's another one....still not the same as mine but looks WAY less costly than the one above.

http://www.amazon.com/OTC-6043-Blas...334&sr=8-2&keywords=radiator+power+flush+tool

The nozzles are for restricting the amount of coolant that is allowed to bypass through the intake manifold. It causes more water to be directed through the block and probably does provide for better cooling in tropical water conditions.

It looks like you will be the forum's resident pre-97 twin expert from here on out.

So, just how does one go about becoming a member of this lucky family of yours for a summer anyway? :~)

I do like your approach but now that you know what to look for, I would find a couple more of the older ones and put 'em up on the auction block and trade up to a nice 9.9 electric start with remote and trim n tilt.

Now THAT'S Cadillac!

Yes, I would think that having a hole directing hot exhaust right back at the engine and trapping it in the case might contribute some to overheating....It certainly can't help.

And that metal piece held with three bolts is the exhaust pipe seal so I would make certain it doesn't leak. The rubber stuff is the gasket material they used to coat it and seal things up. Since the exhaust "maniflold" is water cooled, the seal is there to keep exhaust AND water from flooding the case and the upper part of the extension. So, yes, for $11 and change, I would replace it. If you want to save a couple of bucks on shipping, you could fashion a "re-seal" with some good RTV like "THE RIGHT STUFF" by Permatex. But even a tube of that GREAT sealant will set you back about $1 more than the replacement seal. And, you need to use it up fairly quickly because of a short shelf life.

What I have found with these is that where the water tube enters the block...there is a grommet-like seal there that looks a bit like a "TOP HAT". Where that seal enters the block, there can be some pretty dramatic corrosion and I have had to fill in that area on a couple of engines with epoxy and then rework it so that there was a good "interface" for the seal and tube not to leak. You have to either flip the block upside down to see it or get down on your knees and look up at it. Also, if the end of the aluminum water tube has been moving around because that seal and it's mounting surface is deteriorated, the tube may be junk too.

Any leakage in that area will act as an ADDITIONAL bypass and dump badly needed cooling water from the pump back out of the case. Depending on how bad the leak is, this could cause overheating even with a new pump.

Did you take the engine out of the oil case? If you did, you should see that the oil pick up tube and screen are right there...They should be carefully cleaned. The sump is usually pretty nasty so I can't imagine anyone not swabbing that out while they are in there. The crankshaft should be exposed too so that you can easily check crankshaft thrust and if you are ambitious, you could check the main and rod bearing clearances. The oil pump is always something that should at least be inspected if not measured for excessive clearances.

And, of course....if you thought you might want to replace the piston rings and clean up the cylinder walls....this is also the time to pull the head and give that a whirl....

I know, I know....it sounds like an overhaul....but then....you asked...;~)

Or, you could just give everything a squeeze and a shake and toss her back together.

If you haven't separated the block from the oil oil case, you have to consider how much added work and expense that will be. You will, at a minimum, need a new block to case gasket and the tiny oring that nests inside that gasket for the water passage.

A new gasket for the oil filler housing is always a good idea.

Cleaning the oil pickup tube and screen can sometimes end up with one or both damaged in some way...if they aren't already. It's all doable and it just comes down to how much time and money you feel is warranted to make it more reliable.

You can work on them or you can use them....your choice....until something breaks.