increase in temp w/ 86 Merc 150

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inlgmouth

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I have an 86 Merc 150 BlackMax. It has been running great. This weekend the temp gauge started going up to 3/4 reading on the gauge. Seems ok when engaging prop enough just to slowly move boat and when going to w/o throttle it goes back down. It seems to be a midrange problem. Water pump was rebuilt over the winter w/ a strong telltale stream and new thermostats put in. Thanks for any help. Ihave another problem (new thread).
 
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inlgmouth

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Re: increase in temp w/ 86 Merc 150

Is there a way to test poppit valve? Can it be cleaned or just needs to be replaced? Thanks
 
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inlgmouth

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Re: increase in temp w/ 86 Merc 150

I rebuilt poppit w/ all new parts and still have problems.. Today engine fired right up and idled for a good 1/2 hr. and temp. stayed @1/4-1/2 on gauge. As soon as I opened it up it started increasing, almost to fully pegged b-4 I shut it down. There is a strong telltale all the time. The poppit cover has a small hole at the bottom that always has water spitting out. The other thing is a fuel problem where engine wants to bog down (occasionally) when opening up and choking makes it go. Could fuel delivery possibly make temp. increase. Thanks to all.
 
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inlgmouth

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Re: increase in temp w/ 86 Merc 150

I found another thread saying the water from poppit cover is caused by diaphragm in the poppit leaking causing it to not properly operate the valve. Is this correct? It spits water even at idle. Thanks everyone
 
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Laddies

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Re: increase in temp w/ 86 Merc 150

Yes there its something wrong the valve should not leak at any RPM.
 
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inlgmouth

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Re: increase in temp w/ 86 Merc 150

I just dissassembled poppit to inspect. All parts are exactly same as old. I discovered something. The screw goes through washer and diaphragm and screws into valve w/ spring holding all together. When installing, the base plate does not sit flush on motor and seems to release or push out when bolted down. It seems valve is too long and this is why water is always spitting out. I have tightened it so that end of valve screws flush w/ diaphragm.
 
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inlgmouth

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Re: increase in temp w/ 86 Merc 150

I'm going to try a slighly longer screw to pull spring and valve in tighter. Hard to tell but it looks like screw may have been cut off b-4. It has a squared off end like it was snipped w/ cutters.
 
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inlgmouth

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Re: increase in temp w/ 86 Merc 150

I got poppit to quit spitting (my error). Just got back from lake and is still overheating. Telltale stream is the strongest its ever been. It idled for 20 min. and stayed between 1/4 and 1/2 on gauge. As soon as you open up, temp. increases slowly and will keep going up until I shut down. Is there anything else w/ cooling system I am missing. I am now going to drop lower unit again to check if exhaust tube is in.
 
j_martin

j_martin

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Sep 22, 2006
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Re: increase in temp w/ 86 Merc 150

It would be worthwhile to have a pressure gauge on it. I suspect one or more of the muriad small cooling water ports in the engine are plugged with debris, perhaps old impeller rubber. I once hit a rotten log in the river at full tilt. It was so soft I hardly felt it. Took a month to clean out all the toothpicks in the water jacket.

A pressure gauge would read higher than it should if this were the case.

hope it helps
John
 
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