BF90D overheating at WOT

[MATPOC]

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)

 

[William01]

You don’t mention a water pump replacement, that’s where I’d start. Not just the impeller but an entire water pump assembly.

 

[MATPOC]

You don’t mention a water pump replacement, that’s where I’d start. Not just the impeller but an entire water pump assembly.

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

 

[William01]

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.

 

[jgmo]

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.