150 running hot

J

JOLLYRAWLY

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Sep 13, 2011
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7
I got a 1986 150 mercury last spring and it would run hot below 2000 rpm. Anything above it would run cool. Had a new water plump and a popet valve put on and now it will start peeing but stop after a few minutes of running at any speed. I read another tread about the water passage being stopped up. How can i check for this and how can the passage be cleared?
 
Texasmark

Texasmark

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Dec 20, 2005
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14,558
Re: 150 running hot

If it is a V6 it has a thermostat at the top of each bank of cylinders and below roughly 2500 rpm's where the bypass valves open and provide for much more flow.

If the I6 there is no stat and you must have a bad impeller as ram water is cooling at the higher speed which you don't have at the lower speeds in enough quantity.

Mark
 
C

Chris1956

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Mar 25, 2004
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27,148
Re: 150 running hot

That motor should be a V6. The thermostats should control the amount of water thru the telltale. Below 2000 RPM, the thermostats are responsible for all cooling functions. I recommend you replace the 'stats.
 
C

CharlieB

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Re: 150 running hot

Also double check that the poppet valve is closing correctly, a stuck poppet will allow too much water flow at low speeds and contribute to high temps.
 
j_martin

j_martin

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Re: 150 running hot

CharlieB said:
Also double check that the poppet valve is closing correctly, a stuck poppet will allow too much water flow at low speeds and contribute to high temps.
Click to expand...

To explain this comment, the pump is positive displacement, with the volume delivered depending mostly on RPM's. The poppet is a relief drain. If the poppet is stuck open it will allow the water to drain out of the block faster than the pump can supply it, creating a hot spot at the top.

Check the poppet. If the seat is loose, it can follow the valve out of the casting and jam crosswise, holding the poppet open.

Test the t-stats in a pan of water on the stove. It doesn't help to replace them unless they are bad.
 
J

JOLLYRAWLY

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Re: 150 running hot

j_martin said:
To explain this comment, the pump is positive displacement, with the volume delivered depending mostly on RPM's. The poppet is a relief drain. If the poppet is stuck open it will allow the water to drain out of the block faster than the pump can supply it, creating a hot spot at the top.

Check the poppet. If the seat is loose, it can follow the valve out of the casting and jam crosswise, holding the poppet open.

Test the t-stats in a pan of water on the stove. It doesn't help to replace them unless they are bad.
Click to expand...

The first thing I did was to check the stats in hot water, and they open. The poppet valve,I am not sure about because I had them done by someone else. It is a v6 150. the water plump was in bad shape making me think there could be a blocked water passage. If the water passage is blocked, is there any way it can be flushed out. Any ideas will help.
 
j_martin

j_martin

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Re: 150 running hot

A pressure gauge will read high when it's overheating if outlet passages are plugged.
 
U

ufm82

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827
Re: 150 running hot

If you have a blocked passage there are two ways to clear it. 1) Pull heads/covers/components to gain access to the water passages and clean them out. 2) Refer to #1.

My 150 ate a bunch of river sand a few years back and it piled up in the poppet valve cavity. This sand is talcum powder fine and once settled is like concrete- no amount of water pressure in a normally running engine would have cleared it. I had to pull the poppet out and get the stuff out. There was no other way.

I don't understand the water pump/blocked passage comment unless you meant there was vane damage. Pieces could very well be blocking things if that is what you meant. And yes, as J mentioned, a pressure gauge will tell you if you have a restriction or not.
 
J

JOLLYRAWLY

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Sep 13, 2011
Messages
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Re: 150 running hot

ufm82 said:
If you have a blocked passage there are two ways to clear it. 1) Pull heads/covers/components to gain access to the water passages and clean them out. 2) Refer to #1.

My 150 ate a bunch of river sand a few years back and it piled up in the poppet valve cavity. This sand is talcum powder fine and once settled is like concrete- no amount of water pressure in a normally running engine would have cleared it. I had to pull the poppet out and get the stuff out. There was no other way.

I don't understand the water pump/blocked passage comment unless you meant there was vane damage. Pieces could very well be blocking things if that is what you meant. And yes, as J mentioned, a pressure gauge will tell you if you have a restriction or not.[/QUOTE

I checked with the guy that replaced the poppet valve and he did not replace the seat, The first thing I will do go back in myself and replace the seat and check for any type of build up. If this does not solve the problem I will look into pulling the heads and flushing later this fall. Thanks for the advice.
Click to expand...
 
j_martin

j_martin

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Re: 150 running hot

The quickest and least expensive way to a repair is proper diagnostics.

Get the water pressure gauge.
 
J

JOLLYRAWLY

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Sep 13, 2011
Messages
7
Re: 150 running hot

j_martin said:
The quickest and least expensive way to a repair is proper diagnostics.

Get the water pressure gauge.
Click to expand...
The gage on the boat reads about 3-4 lbs at idel and 8-10 lbs at 3000 rpm. By what I have read the water passage should not be blocked. Clould it must be in the plump or poppet valve?
 
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