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BF90D overheating at WOT

M

MATPOC

Member
I bought this engine used and have gone through a number of issues, it's a later DK4 engine that was originally NMEA compatible and was converted to older electronics (DK0 or DK2) I have gone though the entire parts list and replaced all the non-compatible parts that were left behind (O2 and oil pressure sensor) but everything else is the same, including all 3 temp sensors, also I purchased a complete spare DK0 motor which I'll be parting out once I figure out what I'm keeping for spares, and I confirmed the sensors and the rest of the parts are all the same
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So that's the back story, the issue I can't resolve is described below, also it's on a 20' pontoon
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When I got the engine it had a number of running issues and while chasing those I pulled and cleaned crusty temp sensors in the head and block thinking that inaccurate temp reading might affect the mixture (lean between 2,000-3,000 rpm) but after cleaning the sensors I started getting an overheat alarm at WOT (5,800) I assume before I cleaned the sensors they were insulated enough with crust and did not reach the 75ºC and now that they are reading more accurately they set off alarm and limp mode after couple minutes at WOT. I can run ALL DAY at 5,500 and they stay in the low 70º range (monitoring on the data stream using Heal-Tech)
*Tested all 3 temp sensors with multimeter and on also data stream, everything checks out, using Honda shop manual for reference for Ohms and temps
*Both thermostats and covers are new, covers were warped and leaking
**I was told the original harness and ECU were damaged by seawater from what looks like the block thermostat leaking RIGHT ON THE ECU connector, so whoever replaced all the electronics didn't bother looking for a water leak!!** |
*T-stats replaced as a precaution, both installed correctly 50º and 60º according to manual, but it didn't change anything, still overheating
*Strong water flow from every place I could test
*Did a trashcan with vinegar bath and it didn't change anything, nothing washed out either
*Removed RR to take a look and the manifold, inside doesn't look crusty, anodes are almost new, I might remove the manifold cover but I don't see a point.
*AT SOME POINT CYLINDER HEAD WAS REMOVED
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I'm at the crossroads:
*Do I try another vinegar bath and hope for the best (it was a pain, whole neighborhood smelled like vinegar for days)
*Someone suggested lowering the engine because someone shared a video with a very similar Evinrude(?) overheat issue what was solved by lowering the engine? Lowering engine also a pain as I will have to cut the bolts, they are cheap stainless trash, tried turning one of them and tit immediately stripped, had to cut it off and replace it. Also I have no way of supporting this engine, would have to bring it somewhere with a hoist just to drop it one hole (that's all the room I have)


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You don’t mention a water pump replacement, that’s where I’d start. Not just the impeller but an entire water pump assembly.
 
William01 said:
You don’t mention a water pump replacement, that’s where I’d start. Not just the impeller but an entire water pump assembly.
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What could possibly be wrong with the water pump assembly if I get a strong telltale stream at idle and water coming out of every hole?
I loosened up the thermostat with engine running and the water came pouring out
 
Out of round cup, slightly bent/deformed base plate, worn or missing impeller blades, water tube grommet issues. Tale tell confirms the water pump is pumping, doesn’t indicate how efficient it’s pumping.

Overheat conditions suggest check regular maintenance items, water pump is a maintenance item.

Your description suggests possible overheating with the previous owner, that could/would damage parts of the water pump assembly.
 
Hi,
To answer your question to William01, most Honda impellers typically have six flexible vanes or "arms" to move water. I have seen outboards, that were overheating, seem to have good/adequate "looking" water flow from the tell-tale that had only ONE of those vanes left on the center impeller hub. And, yes, I always find that a surprise that it could be moving water at all! It's fooled me many times.
That, along with the other items he lists in his response to you, have caused cooling problems even when observed flow looked ok.
It got to the point, when I was maintaining rental fleets, that I would pretty much always opt for a "complete" waterpump repair kit anytime I thought it neccesary to replace an impeller. That kit is MUCH more expensive than just the impeller but it can seem TWICE as valuable after you take off the gearcase, replace just the impeller and have to tear it apart again because it still overheats.

It sucks!

But experiences like that had me ALWAYS looking very closely at the liner (cup), housing, cover (base plate) AND the drive key as well as the key cutout in the mainshaft before deciding to ONLY replace an impeller.

Sounds like ut's giving you a hard time so I hope you can get it sorted.
 
My issue with this logic is that it only overheats at WOT (5,800 rpm) I can run at 90% throttle at 5,500 all day long and it flows enough water to cool the engine right up untill that last 10%
Also tried different prop, went from 15p to 17P and it would not get past 5,000, but I could run WOT all day long with 17P prop
 
I don’t know about engine height on a pontoon but I’ve used only a floor jack to move an outboard up or down. Loosen all bolts with the jack taking the load, block the wheels on the jack if on asphalt or concrete. Use a big screwdriver in the top bolt holes to align them in the new location. I use a block of wood on the jack. Works on my whaler and 500lb 130.

I’m with the other guys, replace the whole impeller kit. Or live with 90% cooling efficiency? Replacement may not fix it but it’s very much worth trying imho.
 
For lowering or raising the engine I have read where a guy used the front jack on the trailer and a couple of helpers to support the engine. Extend the jack to maximum height, wood under the skeg then lower the jack which will bring the transom up till the hole align. The trailer axle acts as the pivot point. I’ve never tried it but it sounded like a slick idea…no hoist required.
 
I'll drop the motor this weekend, got better bolts from McMaster, hopefully those don't need to be cut off every time.
Water pump is easy enough as well so I'll get that done over the weekend
 
Interesting twist: I got a parts motor that came with some generic 13x15 "Captain" brand 3 blade prop and with this prop I can run WOT at 6,000 RPM all day long. Lengthy Ai chat revealed that I might have bad poppet valve, ailing impeller, scored impeller housing, or it's possible that my slightly dented 4 blade prop is causing enough turbulence and cavitation to send the air bubbles into the water intake and cause overheating.
I'm gonna replace the complete impeller housing and get a new stainless prop
 
I would ignore AI’s solutions, they are very generic and draw from data on many brands of outboard. Your 4 blade prop may be too much “load” for your Honda’s torque curve . Kinda like putting a 35 inch tire on a 4 cylinder 1960 VW.
 
NSDON said:
I would ignore AI’s solutions, they are very generic and draw from data on many brands of outboard. Your 4 blade prop may be too much “load” for your Honda’s torque curve . Kinda like putting a 35 inch tire on a 4 cylinder 1960 VW.
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Ai isn't all-knowing but bouncing ideas off the Ai and questioning it's logic rather than blindly following it's advice got me to the point where I finally solved this problem!
It wasn't the prop causing it but also it wasn't far off on the theory of air being inrtoduced into the cooling system: being the pontoon I have water deflecting off the tubes converging dead middle of the deck, hitting the cross beam it creates an area of severe turbulence which is aerating the water. With 4 blade prop at full chat it was enough to pull the bubbles down towards the water intakes and into the cooling jacket.
How do I know? I underskined the toon and overheating stopped, also it dropped 200 rpm (from 5,800 to 5,600) while still reaching same top speed, which suggests that prop was slipping more due to aeration
So based on lengthy Ai chat I came to conclusion that I can stay with same 13x15 dimensions but switch to 3 blade and pick up another 100-200 rpm to get it back to the sweet spot of 5,800, also switching to stainless prop (sometime down the road) will minimize blade deflection and increase efficiency. Lastly I can get Solas NS3 for about $250 (I already have the Rubex hub which is an extra $50) vs buying same exact Solas with pressed hub for $400
 
NSDON said:
Good use of AI and common sense.
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Absolutely, I hate when people just blindly follow Ai thinking it's some kind of all-knowing god-like creation while it's simply a search and summary tool that utilizes a user interface that is designed (by humans) to mimic human interactions.
 
I find AI is good for common problems with common issues. It’s a generic checklist of things to check. I worked on a Clarke Troller once, nothing in AI for it.😁
 
NSDON said:
I find AI is good for common problems with common issues. It’s a generic checklist of things to check. I worked on a Clarke Troller once, nothing in AI for it.😁
Click to expand...
It's possible that if you posted something somewhere about that Clark it would have found it and stored the info making it available to future searches.
 
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