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BF150 Over Heating Part 2

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PaulBF150

Contributing Member
I have a long history with this issue.
This past winter engine overhaul, all water passages cleaned and checked. New fuel injectors (not that I had fuel issue), new water pump (3rd one), new thermostats, checked resistances on temp sensors. This time I installed external Oil Cooler and also external high pressure water pump injecting fresh water into top exhaust service ports on manifold. Also ported the 2 water tubes on top of exhaust manifold directly out of the engine.
Put boat in water 2 days ago. today took it for a ride. Without the High-pressure water pump on, it took a bit of time once on plane to throw Overheat alarm. Then I turned on the water pump and that extended the period some more, but soon after the alarm once again. With the water pump I installed a solenoid on the lower service port and having the pump on the top service port. Therefore, both service ports getting cool water. With everything operational the engine did not throw any overheating alarms.

Anyone have any idea why this engine is running HOT?
 
Hi Paul,

Those are some interesting add ons and sound reasonable to me. I'm sure you may have already considered this but, hopefully, you didn't introduce a flow issue doing them.

I'm no expert by any means but hear me out:

Outboard motors have to work much harder than, say, a car or truck engine with lots of gear ratios to keep the rpms down (typically under 3,000) at higher speeds.
It's been said, by folks much smarter than I, that an outboard "is always running uphill".

Just guessing here but, coupled with the heavy work load outboards have, it's possible that your engine is running on the lean side of the air/fuel equation. That would increase combustion chamber temperatures and might lead to the overheating you're experiencing.

I guess I would start by analyzing the spark plug coloration.

Are those new injectors OEM?
Is your fuel pressure optimum during high speed operation?

If this were a car I would "T" in a fuel pressure gauge, tape it to the windshield and take it for a hard run. But, obviously, it's a bit tricky doing that in this situation.

if you could monitor the 02 sensors that might tell you something.

Just throwing out ideas and it's only one possibility but maybe something to keep in mind while trying to figure this out.

Good luck.
 
Thanks for the reply.
First the increased volume of water traveling through the exhaust manifold had me concern a bit. Last year I ported the water directly out of engine rather than running that water down into exhaust. that helped significantly.
I can closely monitor Cylinder, Block, Case and Exhaust temperatures via a microcomputer monitoring the 4 sensors.
Surely my Megyer add-ons do change things, but I found to be a good thing.

Those things are attacking the result of a HOT situation. Plugs are clean tan in color (last year replaced them). Fuel pressure Hi side was about 125psi, if I remember correctly. New OEM Injectors. As for o2 sensor I previously asked question whether engine might be running lean or rich. An expert said he hardly sees them go bad. Of course, the ECM is not reporting an issue (at least from counting blinks). But I will put a DVM on the sensor and monitor it. Then I will measure the o2 sensor on the other engine and compare results. The other 150 engine is running good (knock on wood).

More Ideas are greatly appreciated.

Paul
 
One other thought about what causes engines to run hot is ignition timing. If ignition gets advanced too much, that can set up a situation where combustion is so early that the engine is sort of fighting against itself. Over advanced ignition is similar to detonation and has been known to burn holes in pistons. The only "rub" to that theory, in this case, is that I don't believe you can adjust ignition timing on these engines. For most newer, fuel injected engines, the ECM is fully in charge of that. So it likely wouldn't apply but thought I'd mention it.

I don't work on these and the major part of my engine experience is with cars and trucks. But there is a similar set of physics taking place with any IC engine. One thing I learned early on about heat rejection in a car's engine is the "1/3 rule".
It's an approximation and isn't near being exact but it gives a general guide as to what is happening.
It goes:
1/3 heat of combustion is removed by the cooling system.
1/3 by the exhaust system
1/3 by radiation.

Of course, the last one, radiation, is usually not 1/3 and, on an outboard, probably way less.

But this does point out the absolute importance of the exhaust system removing heat.

Obviously you've tried to address this with your innovations but have you looked at the "gate keepers" that let the heat out of the cylinder? The valves? Are they timed correctly and are they opening adequately?

Just some thoughts.

Hope you get it figured out.
 
I hope the ECM is smarter than me!

This engine has to be running Lean and causing increased exhaust temperatures. Not sure what I can do about that. Only solution is to confuse the ECM, maybe play with O2 sensor voltage.

As for the valves, this winter I had to replace 4 of them (bent). Funny part of that was I had good compression (125psi) before I took the head off the engine. Then reinstalling the head and rechecked compression and Cylinder 1 & 4 was zero. Taking head off again found the valves bent. Now the cause was likely a result of me troubleshooting what was causing Engine shut down. In doing so did cause some instances where exhaust manifold was burning the paint. With all this said, all valves were lapped in and gaps adjusted, and compression rechecked. Aligned all timing marks and buttoned up the engine. And it ran when I cranked it over (Happy Days).

The more I think about it, I need to check the good engine O2 signal level and compare with the not so happy engine. From that I might be able to alter signal levels.
 
Well, my experience is that O2 sensors fail completely and provide no signal or they get "lazy" and provide a "confused" signal that usually causes surging at worst. I don't know that one could "convince" an ECM to drive a fuel mix lean enough to burn paint. When I suggested monitoring O2 activity it was more about looking at the exhaust content rather than thinking the sensor might be the reason. But, it wouldn't be the first time I was wrong.

You might try unplugging the sensor and see what pops. You should probably get a code but maybe not. But that should put the computer on a default strategy for fuel control.

I would be more inclined to suspect a vacuum leak, poor fuel delivery or even a bad TPS or throttle body for a very lean condition.

A MAP sensor can drive the mixture very lean by reporting low atmospheric pressure. I've seen that with no codes before too.
 
First the burning paint was associated with faking the ECM with a decade box so it was thinking all was okay. Meanwhile as I was monitoring the Exhaust water temp Sensor, things got a wee HOT all of a sudden. This told me the Exhaust Sensor is the one that enable the ECM to shut down the engine. The others just report status and will not cause engine shut down.

I'll look into vacuum status.

Pertaining to atmospheric pressure there is a soft fault reported by the ECM for the Barometric Sensor. I replaced it with new one and ECM got upset and triggered an alarm. Putting back the old one no alarm just the soft code. Maybe I need to investigate both MAP and BARO sensor operation. Also check good engine to see what it measures. Wow all this homework I got assigned. I'm tired already!
 
Yes....fun while boating! Not so much while studying/working.

You might be on to something with that baro sensor....
I mean, if the computer thinks you're at 8,000-10,000ft. it's gonna lean that baby way out!
 
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