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Maintence / Questions / Tutorials Thread, Yamaha 70 overheating in TribeNwater Boats; As some of you know I have been having trouble with my engine over heating. I thought I had found ...
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Old 02-05-2008, 08:09 AM   5 links from elsewhere to this Post. Click to view. #1 (permalink)
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Yamaha 70 overheating

As some of you know I have been having trouble with my engine over heating. I thought I had found the problem with a gummed up Thermostat. I replaced the thermostat, and a test run up the river didn't produce any overheating.

Last weekend I went shad fishing, and didn't make it 200 yds from the ramp and the overheat alarm went off.

This past weekend I decided to tear it down and see what I could find. Let me start by saying, "I'm no mechanic". Well, the first order of business was to get the bolts out of the cylinder head. This was my go or go to the mechanic point. If I could get the bolts out, I was going forward, but I did not want to end up with broken bolts in the block. Amazingly they were all pretty easy, except for the bottom two bolts. Slow steady pressure did the trick though, and I was able to get them all out.

I pulled the head cover off, and was greeted with This:


This is the inside of the head cover:


Next I decided to pull the exhaust cover and exhaust manifold to see what things looked like in there. At this point I hadn't mustered up enough nerve to pull the cylinder head.

Here's a pic with the outer and inner exhaust covers pulled off. This was after a little cleaning. I forgot to take a pic when I pulled it off.


Well, I had made it this far so next up was pulling the cylinder head. Yikes:


It was hard to get a good pic, but the bottom cylinder was completely covered in what ever this stuff is. I soaked some rags in 2 stroke oil and packed them in the cylinders, to try to keep any water out of there. I started cleaning with some salt away, and any little scrub brushes I could get my hands on. I then used some CLR, in a squirt bottle, and some more scrubbing and scraping. Finally I got to this point:



Now I had to clean everything else. Here's the line up after a first round of cleaning:


And the outside of the cylinder head:


One of the hardest parts was getting the old gaskets off. Lots of scrapping and scrubbing again, but I finally got them clean. Next up was new gaskets:


Everything went back together without incident. I coated all the bolts with anti-seize, and torqued them down to spec. Cranked it up on the muffs, and ran it for about 15 minutes. It didn't blow up, so that was a good sign . It was getting about dark by now, so that was it for the day.

Last night I came home and ran over to the river for a test run. I ran her for about 30 minutes or so, and didn't have any problems. Let's hope that I finally got it this time :fingerscrossed:

Eric
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Old 02-05-2008, 08:33 AM   #2 (permalink)
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Eric not trying to be a **** but I'm not sure why any of that would fix your overheating problem.

Have u replaced the impellor yet?
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Old 02-05-2008, 10:26 AM   #3 (permalink)
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Haven't replaced the impeller, it was replaced last summer, and it seems to be peeing just fine. If I have any more issues I will look at that next.

If nothing else the cooling system is nice and clean now.
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Old 02-05-2008, 04:18 PM   #4 (permalink)
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I figured someone would chime in with "have you replaced the impeller yet". Eric, I'm sure you remember my long story while we were down in Flamingo about the Yamaha overheat problem. I figure my story had something to do with you taking the engine apart. Low and behold, you found a mess. Good job doing yourself. If I was your age I'd probably do it myself too. At my age, I just take it to the man.

For the rest of you, here's the abridged version of the story. The Polar boat w/90hp Yamaha that I sold to TitusvilleTom 3 1/2 years ago had the same problem early last year. I had never heard of such a thing. Then while I was in the process of selling my Mitzi w/70hp Yamaha, it too started overheating. I took it to Marine Specialties, they did the obvious and replaced the impeller.... still overheated. Mark then had to remove the heads and clean the water ports. This on an engine with only 130 hours and got fresh water run thru it every single time it went into salt water.

Anyway, glad it worked out for you Eric. If I ever have the problem again I'll call you!!
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Old 02-05-2008, 07:40 PM   #5 (permalink)
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Wow. I'm barely competent when it comes to removing the cover off the top of the motor. Sometimes I have trouble hooking the hose up to the ear muffs.
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Old 02-06-2008, 11:29 AM   #6 (permalink)
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Phil...How could I forget

The motor is 7 years old, so I figured it was due for a good cleaning anyway. I spoke to 2 different yamaha mechanics, and they both had their stories of the same issue. The guy at Hontoon said the boats from the river get some kind of cottage cheese looking stuff in them that is really nasty.

Looks like a decarb, is the next order of business.
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Old 02-07-2008, 05:50 AM   #7 (permalink)
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Great job Eric! Awesome pictures, too. Decarbing every now and then definitely keep her clean.
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Old 02-12-2008, 05:04 PM   #8 (permalink)
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Eric
When you are ready to decarbon, go to an Evinrude dealer and get a can of engine tuner, run motor on hose and spray tuner through carb throats. You will get lots of smoke and will have to idle engine up a little to keep running. I hate saying use Engine tuner being a Yamaha tech, but that stuff is the best on the market. After you have fogged it down, let sit for a day, add a little extra oil to the fuel and take to water and run. Do not run WOT for 10-15 mins. After it is all cleaned out, change the spark plugs and go fish!
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Old 02-13-2008, 03:38 AM   #9 (permalink)
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Welcome Loye! Eric, Loye is the flippin' man. Only guy I trust to talk to about my Yammy.
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Old 02-13-2008, 08:14 AM   #10 (permalink)
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Awesome, Thanks Loye!!
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