Need help diagnosing Force 150 cooling problem

[HotTommy]

I need advice to diagnose a cooling problem on a 1993 Force 150 outboard. Here are the relevant facts.

1. Engine ran well with no obvious problems for several months last summer. It is used mostly in deep lake water.
2. While running at about 4500 RPM, the engine started losing power and I slowed to idle. Moments later the overheat alarm sounded and I shut it down. We were towed in.
3. Tear down revealed damage to the #3 and #4 rings and pistons.
4. I did not resume the repair until a few weeks ago.
5. As the #1 piston was replaced two years ago, I went ahead and replaced all four of the remaining pistons with Wiseco.
6. I did not see any specific root cause that started the damage. As the #3 piston has its own carb, and #4 and #5 feed from the same carb, I was doubtful that the problem was caused by a lean carb situation.
7. With the engine reassembled, I put it on a set of water muffs and started it up. I let it run for 15-20 seconds before shutting it down due to no water coming from the telltale on the thermostat housing.
8. I replaced the water impeller with a new one. The old one was less than two seasons old and did not appear to be damaged.
9. I ran the engine on water muffs again and saw only one small trickle of water from the telltale. I shut it down after about 15 seconds.
10. I removed the thermostat and confirmed that the passage to the telltale was open. There was some small debris in the thermostat consisting of a small piece of plastic and a leaf. I replaced the thermostat housing without the thermostat and ran the engine on muffs again. Again there was no flow from the telltale so I shut it down.

I've read some of the other threads regarding lack of water flow. Keep in mind that everything worked before the engine failed last summer, and I did not change the impeller until I confirmed that there was no flow. I was careful to get the key in place, so I doubt the impeller was the problem. The problem existed before I changed the impeller so its doubtful misalignment of the water passage caused the original problem. My best guess is that there is an obstruction somewhere, but I don't know how to go about finding and/or clearing it. I welcome any advice that may help.

 

[HotTommy]

More clues:

I don't know what the flow of cooling water is supposed to be, so my assumptions about what to expect may be wrong. But here's what I saw.

1. I removed the gear housing to expose the water line that mates to the top of the water pump assembly.
2. I removed the thermostat housing and using a water hose at low volume, I forced water into the opening that normally holds the thermostat. Within a few seconds water came from the area of the leg that holds the water line. I could not hold the hose and see the bottom of the leg at the same time. It seemed to me that the volume of water coming out the bottom was less that was going in to the thermostat opening.
3. I then reversed the position of the water hose and used my hand to make a good seal with the water line at the bottom of the leg. Water flowed into the line for 10-15 seconds before a few small drips fell back down from inside the leg. Water did not come from the telltale or from the two holes near the top back of the leg. When I pulled the hose from the water line, a large steady stream of water flowed for 5-8 seconds. It was if the water had accumulated somewhere and was draining back out.
4. I ran a wire up the water line to check for obstructions. I felt nothing until the wire seemed to touch metal near the bottom of the block.

I assume that the normal flow of water would go from the pump (impeller), up the water line in the leg, through the block and eventually to the thermostat housing. I am seeing no indication that the water is moving from the bottom of the block to the thermostat housing.

 

[HotTommy]

A little more searching revealed this thread about a problem similar to mine. It sounds like I may need to remove the exhaust cover. Does that sound like the next logical step?

 

[pnwboat]

Yes the exhaust cover would be the next thing that I would remove to check for obstructions. The water flows from the water pump up to the adapter plate between the motor and lower leg, then up the exhaust cover to the top of the block and to the water jacket on the left side of the cylinders. It flows down to the water jacket around the bottom cylinder, then it flows up the right side water jacket around the cylinders to the thermostat. After the water passes the thermostat, it flows down the water jacket in the head to the bottom of the block and gets dumped out the exhaust.

Kind of a pain on the 150HP motors. Some of the lower bolts are hard to get at. You can remove the bolts that hold the lower cowling in place. Then you can kind of shift the cowling to one side for more room to get at the bolts. Also be careful not to snap any bolts. They're 1/4 X 20 bolts and are often corroded and need gentle persuasion to remove.

 

[jerryjerry05]

You put water up inside the motor from the tube that the pump feeds?
With a light and a low pressure hose hook water to the feed pipe and slowly turn water on, all the time looking up inside and seeing if the waters leaking at the seal where the pipe meets the block.
When you had the block off did you put too much silicone on the adaptor plate??

 

[HotTommy]

I didn't take the block off. I'm pretty sure the water flow problem I'm seeing now was what caused the engine failure last summer. That means it happened before I replaced the pistons.

 

[HotTommy]

Now this is fun. There are more than 30 steel bolts that have been anchored in aluminum near a hot exhaust for about 25 years, and so far about one in five has broken off. If things don't start looking up tomorrow, I may have a parts engine on my hands.

 

[tommarvin]

HotTommy fear not, snapped bolts.
Grind the bolt flat, center punch a dimple/indent at center of bolt, start with an 1/8 inch cobalt drill bit, then 1/16 inch larger until you get to Helicoil drill size for tap.
Shops will remove snapped bolts too.
But wait it get's better, there could be an obstruction in the head too.
Just think how easy it will be to remove the bolts next time?

 

[jerryjerry05]

Pastorbud might have a 150 powerhead ??
​I think he's trying to swap a 125 to a 150 and he's not having much luck???

 

[HotTommy]

OK. I've officially lost my interest in this old engine. It's got lots of new parts, so I'll be selling it to recoup some of my expenses.

 

[tommarvin]

1. Work on your motor after the boating season ends, a winter project with lots of patience, if you can get it to my house I will do it this winter...you buy the parts,deal?
2. Keep snapping bolts, don't give up now, keep going, take the power head off.,take it to a motorcycle machine shop, your going to be thousands ahead..
3.Your going to spend thousands more for an unknown product.

 

[HotTommy]

Thanks for the generous offer Tom, but my next engine will be brand new. This old one is for sale on CL in Auburn, AL.