Yamaha 4.3 Sterndrive Running Hot Mystery

Swampmouse2

Seaman
Joined
Mar 26, 2014
Messages
52
Hey Guys,
I got something that I am completely stumped and am just looking for a little advice before I take it to the professionals at the repair shop tomorrow. I have 1992 Yamaha 4.3 stern drive. When I put her up for the winter, she ran like a top! No issues at All.

I got a new impeller from Capt. Ken and put her in..everything good on that front. I took her to the lake the other day and fired her up. By the time I got out of the no wake zone (50 yds.) and romped down on the throttle, I started running hot almost immediately. I cut it off and got a friendly passerby to give me the short tow back to the dock.

I was thinking thermostat....so I took it home, removed the thermostat, rtv'd the housing back together, and went back to the lake.
Without the thermostat in it, it was running great for about 5 minutes, water temp was staying around 125-130 degrees. When I got back to the bouys, I noticed the temp started going up quickly. I ran it another short distance, and sure enough up it went again to about 200-210. I quickly got it back to the dock. That was without the thermostat in it. Seems like I read somewhere that that motor will not cool correctly if the thermostat is not in it???? By the way, just as a side note, I put the thermostat in a pot and it was opening and closing at temperature ( I believe it was opening around 150 , with no gaps or holes in it when closed either.

I know the water pump is pumping because : 1) I physically put my hand on the impeller cover when the motor was running hot and it was cool to the touch, 2) when I was replacing my impeller (at Capt. Ken's advice - thank you Capt.!) I sucked on one of the ports and was able to draw suction and hold it against my hand on the other port for a while.

I also checked for debris at the power steering oil cooler, and even back flushed the hose going from the oil cooler to the thermostat housing from the top down. There were a few small pieces of impeller vanes in there but nothing major to clog water flow. (I had already cleaned that before I winterized it)

Also the oil is crystal clear - no water in the oil.

I am at a loss at this point.

Anyone got any suggestions on another part that may have went bad??

Thanks!
SM
 

Swampmouse2

Seaman
Joined
Mar 26, 2014
Messages
52
Ok after reading my book more carefully, I now realize that it is the water pump / recirculating pump for the motor itself. I was hearing a little noise from the starboard side of the engine, and that has to be it. I am a little embarrassed to say that I didn't realize that motor has a sea water pump AND a water pump like those on a car! DUH! I feel really stupid now. I guess I am definitely learning about I/O engines! I will probably go ahead an take it in to the shop, and have him call Capt. Ken to get the parts. At least I feel better about knowing what it most likely is. SM
 

Bondo

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Apr 17, 2002
Messages
70,470
Ayuh,.... Are the exhaust manifold water passages clear,..??

If yer pumpin' water Into the motor, the water has to be able to get Out too,....
 

Swampmouse2

Seaman
Joined
Mar 26, 2014
Messages
52
That's a good question Bondo. I am not sure. Since we have a lake house booked week after next, I went ahead and took it on to the repair shop. Killed me to do it, but I figured just in case I don't have the time to get it all pulled apart next week, it will be money well spent...I guess. I think it is the water recirculating pump because I was hearing some strange like squeaking from that side of the engine. Nothing out of the weep hole to tip me off, but I was hearing a little noise over there. I will let you know how it goes.

Thanks,
SM
 

Swampmouse2

Seaman
Joined
Mar 26, 2014
Messages
52
So the mystery continues. I REALLY hope Capt. Ken sees this and has an idea........
I put the boat in the shop a couple weeks ago and they put a recirculating water pump in it. I had forgotten to leave my screw in plug with them, so I ran it back out to them yesterday afternoon so we could test it out. We backed it in but left it on the trailer. I ran it up around 2k rpm's. After the thermostat opened up, the temp gauge kept right on cruising up past 200. They then asked about the seawater pump impeller, and I had just replaced it a couple weeks ago. They then asked me about the impeller in the foot, which I told them I was not aware of one in the foot. The guy who runs the marina told me something along the lines of "all motors have an impeller in the foot" . We then discussed some ideas collectively with their mechanic who had walked over to the ramp to see how the temp was going.
I mentioned Bondo's suggestion above...."could it be the exhaust manifolds are clogged with rust or something". Neither one of them thought it would be that. The mechanic "thought" it was exhausting properly.

So Bondo....how do we check to see if it is actually exhausting properly?? Do the manifolds have to be removed and be inspected for a blockage?

So far, this is what has been done:
seawater pump impeller changed out, the power steering oil cooler hoses pulled off to check for old impeller pieces blocking the water flow, backflushed through the top of the oil cooler hose to get all said possible impeller pieces, thermostat removed and tested - opened and closed at temperature and sealed completely, boat ran without thermostat and still ran hot, thermostat put back in, and still runs hot, recirculating water pump changed out (the old one was starting to squeak at least and they said it was starting to leak through the weep hole as well), STILL RUNNING HOT......ARRRRRRRGGGGGGGHHHHHHH!

Anybody have ANY other ideas here??????

I know I shouldn't have to be consulting with the very mechanics I took it to (because I thought they should know more than me about boat engines), but that's where I am at right now. Any feedback is GREATLY appreciated!!!!!

Thanks,
SM
 

Swampmouse2

Seaman
Joined
Mar 26, 2014
Messages
52
I forgot to mention that the mechanic called me this afternoon and told me it did NOT have an impellar in the foot. He pulled it and there wasn't one. Probably why the book didn't mention it.....hmmmm.

SM
 

Bondo

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The mechanic "thought" it was exhausting properly.

Ayuh,.... On muffs rather than in the lake, you can better tell what's exhaustin' where,...

In the water, is there water available to the raw water pump,..??

Take the raw water pump intake hose off, 'n flush both ways to test flows,....
 

Swampmouse2

Seaman
Joined
Mar 26, 2014
Messages
52
Thanks Bondo. I know when I ran it Memorial day without a thermostat in it, the raw water pump was pumping because I put my hand down there on it and it was cool to the touch, even with the engine over 200 degrees. He did put it on muffs today and said he was about to start pulling hoses and checking for water flow. He shot the exhaust manifolds with an infrared thermometer and they were definitely over 200, and somewhere else wasn't.. I believe that's what he was saying this afternoon. So, that's why I kept coming back to them...some reason water isn't getting to them or not getting out of them.

SM
 

Antax

Seaman
Joined
Apr 23, 2012
Messages
61
Just a note.. If your 4.3 is the same as my '92 5.7 the water doesn't exhaust through the manifolds. It exhausts through the risers. The water circulates through the bottom of the manifolds, into the bottom of the riser and back to the engine. The housing below the thermostat housing has a diagonal "plate". The hose on top is the one that exhausts the water.
 

jniece

Recruit
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Jul 30, 2015
Messages
2
Thanks Bondo. I know when I ran it Memorial day without a thermostat in it, the raw water pump was pumping because I put my hand down there on it and it was cool to the touch, even with the engine over 200 degrees. He did put it on muffs today and said he was about to start pulling hoses and checking for water flow. He shot the exhaust manifolds with an infrared thermometer and they were definitely over 200, and somewhere else wasn't.. I believe that's what he was saying this afternoon. So, that's why I kept coming back to them...some reason water isn't getting to them or not getting out of them.

SM

So what is the final word? Did you find out what was wrong?
 

Swampmouse2

Seaman
Joined
Mar 26, 2014
Messages
52
I wish I had a great end to this saga, but unfortunately it still continues. After the mechanic replaced my water pump and still running hot, they replaced the temp sending unit. Told me it was fixed and all was well. I went down to the lake and took off across the water. Stopped after a little ways to check, and something smelled a little funny, but I could not see any major problem. I assumed it was the oil burning off the new water pump ( you know parts sometimes have a thin film on them to keep them from rusting). I checked it a few times and kept running the boat, but kept smelling the funny smell. The water temps were showing ok. I Headed back because my gut and my nose kept telling me something was still overheating. I got close to the dock and checked again and smoke was boiling out of the motor compartment. The exhaust manifolds were toasted. The paint burned right off of both of them. So....after an acid bath and inspection, the mechanic says they are not cracked. He started backflushing all the hoses and thinks they have it found. There is a hose that goes from the water intake in the out drive and runs through the transom and I believe to the seawater pump. When that one was backflushed, water poured out at the transom, so they think there is a crack on the bottom side of it. They have pulled the out drive off but cannot get to the hose because on the large "bracket" (I don't know the correct terminology for it) that the outdrive connects to at the transom has some crazy looking star screw that they nor I have ever seen before. It looks like a 12 point allen or star bit basically. The mechanic says he has searched several tool places and even spoke to another mechanic to try to figure out what sort of bit goes in it. Its pretty large. Sort of like a giant set screw almost, but about 1/2" - 5/8" in ID. Any way, I am going to take a picture of it and go to northern and start the hunt for that tool. Once they remove those 2 special screws, that bracket will be removed and the hose exposed. It has been extremely frustrating. I wish I had just been patient and did all of this work myself, but I felt like I didn't have the time to do it. Lesson learned! I think when its all said and done, I will have paid about $1400 for a recirculating pump, a sending unit I did not need, and a rubber hose. Ouch.

I have spoken with Capt. Ken and if this hose does not fix the issue, I will be taking it down to PCB, FL to Capt. Ken to work on over the winter.

Once fixed, I will try to get this thing sold next year, and look for something with a Mercruiser in it. Parts are readily available, and if I get stumped, I can take it to many Mercruiser specialists around here.

Once finally done, I will re-post so others with a Yamaha 4.3 will know. I will say this...if it is the hose we think at this point, that sucker is dang hard to get to! The whole outdrive has to be removed all the way to the transom to get to it.

SM
 

Swampmouse2

Seaman
Joined
Mar 26, 2014
Messages
52
OK guys...this answer was a long time coming but i wanted other Yamaha owners to know the deal.....

Sure enough, the hose/tube (actually its more of a hard plastic tube) had a crack in it, and the complete outdrive had to be removed. This piece actually goes through the transom wall of the boat. Apparently, the crack was allowing it to suck air instead of water at running speeds, BUT it was getting enough at idle to not have the problem...or at least they told me that, and from my test drive, that does seem to be true.

So...to recap, the motor ran hot (VERY hot at high speeds, and did not at idle. Replaced the water pump and impeller, etc. By the way, muffs wont do on this outdrive.....i learned the hard way. Not enough pressure to push it through the motor for cooling.

Capt. ken can order it for you, but its quite the job for a little tiny plastic tube about the size of your middle finger.

Thought maybe this may help someone.

Now if I can figure out what the "mechanic" did to screw up my Tilt / trim solenoids so as to make the tilt / trim inoperable!!!!

Save yourself some time, money, and hassle guys. Do it yourself if you can!!! Don't settle for somebody that says they can do the job on these motors unless you are sure they are a good mechanic. It cost me my boat for 10 months, and it still is not fixed (tilt / trim)!

SM
 

Bondo

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Messages
70,470
Apparently, the crack was allowing it to suck air instead of water at running speeds, BUT it was getting enough at idle to not have the problem...

Ayuh,.... Sittin' still or at displacement speeds, that fittin' is under water, so it would still suck water,....

On plane, ya it's outa water, 'n will suck air,.....

Glad ya finally found the problem,......

For the trim, look over the wirin' at the pump,....
Something mighta been knocked loose,....
 
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