Over Heating Yammie 1992 150 2stroker.

[willy]

Went down today and did some work on my V, changed filters etc. was going to go out, it was on a work station and I was running the motor on muffs, started fine as normal, after running for about ten minutes all of a sudden the overheat alarm sounded, I checked quick and the hose was going good, the pisser was pissiing so I shut her down and started checking. Pulled the cover off and felt the engine by the T stats and could not keep my hand on the heads, both sides the same, hot,
Checked for anything visible and nothing, had good oil flow. Engine was running nice, sounded real good, no missing, idled fine. Pisser was not a hard straight jet stream but was what I thought would have been a good flow. Exhaust was clean standard looking smoke.
When engine cooled down I restarted and same thing happened within a couple of minutes so I shut down, engine was again to hot to touch.
Spoke with Skools and he suggested I pull the T stats, I did and though they were definetly used they were not corroded or frozen.
I re installed covers and kept the Tstats out figuring it would run cool now, nope, upon restart heated right up, both sides the same.
The water pump was done for last season by the mechanic of the fellow I bought the boat from and has worked fine no issues till now.
I am planning on pulling the lower unit and checking the water pump out but any other suggestions would be appreciated. The fellow who owns the marina I am at said that the pump could still be bad and the pisser could still flow, especially on the hose because the hose provides pressure, but he also said that it would be unusual for it to get that hot with Tstats pulled and running on a hose and muffs to get that hot that fast.

[Seacrets]

I'd recommend if you pull the lower unit, change the whole pump and not just a kit. If it still overheats, then I'd recommend flushing the water jackets with a descaler.

[Monkey Butler]

I was having an overheat on one bank on my 1986 V6 so I decided to do a little investigating. Take a look at the video on the link below.

Here is what I found when I pulled the T-stat covers and ran the motor. At idle even with a new impeller the flow of water thru the T-stats is not very much. If you look at the video right below the hole for the T-stats there are 4 small holes where water re-enters the head covers. The water then "falls" down thru the head covers and then I believe it goes thru the poppit valve. If the poppit is stuck open it would let the water exit the motor before the cavities in the head covers was full. Notice where the overheat sensors are compared to the water passage. I'd check the poppit valve first. Other than that do you know if the impeller was replaced with a genuine Yamaha part? I've heard that the Sierra's don't pump as well the Yamaha's do so I pay the extra for a Yammie part. Oh, and the pisser can flow what looks like a decent amount before any water actually flows uo to the stats. I noticed that if you rev up the engine and don't see an almost instant change in flow from the pisser then that means you are filling up the block before the pressure rises enough to see an increase at the pisser.

With all that said I also find that mine still runs hotter on one side when on the muffs than when its in the water. When you think about it when the boat is in the water at idle the pump is totally submerged. On the muffs you are relying one the hose to push the water up to the pump and then for the pump to lift it like 3-4 feet to the top of the block. I'd launch and see if you still get an overheat before you throw a lot of money at it.

Good luck, hope you get it resolved.

Steve P.


http://www.monkeybutler.com/boat/MVI_1589.avi

[willy]

Thanks MB, where is the poppit valve and how do you check to see if it is working?

[Monkey Butler]

It is on the lower right of the exhaust cover on the back of the powerhead. It's the thing that looks like a thermostat housing in this picture.

http://www.monkeybutler.com/boat/yam...n/IMG_4548.jpg

There is a rubber grommet in there that you should replace as a maintenance item along the same schedule as your t-stats. Also, Yamaha changed the design later on so it was less likely to get stuck open by debris like sea grass. If you go to

http://www.yamaha-motor.com/outboard/parts/home.aspx

and browse to your motor look at the tab for "CYLINDER CRANKCASE" and parts #48 to 51 will get you the new design.

Also, if the pump was just done then when you pull the lower unit check to make sure that the rubber grommet that the water tube plugs into up in the mid section is in place or you could lose water pressure there too.

Steve P.

[willy]

Thanks, something else for me to check this weekend.
And the pump was done before last season, something happened since the last time I had it out, four weeks ago and today.
Now I did use flush away on the motor, I have the flush system that you attach to the hose. I am wondering if something could have gotten dislodged from the flush and cause a problem. Just reaching for ideas I guess.

[phatdaddy]

willy, i've got a 150 yamaha on a 19' cc and it does the same thing. if i run it on the hose, the horns go off after 10 minutes. i run it on the muffs & a hose to the flush port, no problem. i know its a pain, but try puting it it the water and see if it repeats.

[spareparts]

Yamaha recomeds using the flusihng attachement and the ear muffs , both connected to a dedicated water supply when running their V6's on a hose. Teh Yamaha water pumps have several places(water drains) that will suck air when you run it on a hose. Try using the flushing attachement and the muffs, see if it overheats then. Worse comes to worse, take it to the boat ramp and stick it in the water

[Blue_Runner]

Good info. I don't like running mine on the hose because it doesn't seem adequate. I think I use the double hookup idea going forward. I know you should NOT crank the engine using just the flush attachment...I read that in the manual after a friend said it is ok. Can't believe everything you hear.

[willy]

Well I am going to change out Tstats because I have them out already and try it in the water first as all advise. Come to think about it I was in full hot sun and it was running for at least ten to fifteen minutes when it happened so hopefully that is all it is.
Say a prayer