Mercury 150 Overheating

[mike-wright]

Mercury 150 Overheating

I?ve been struggling with an overheating problem for two years now. To make a long story short, at idle to max speed, and anywhere in between, the motor will slowly heat up to 180. That triggers the overheating alarm and I shut the motor off.

I have changed the warning module, water pump, thermostats, water lines, poppet valve, temperature sensors, temperature gauge, water pressure gauge, checked oil injection, cylinder compression test, probably more parts I?ve changed, but forgot.

I have great water pressure, motor runs great; no problems. When I am at home running the motor off the garden hose, motor heats to 140, and never above, no matter how long I idle or give a little gas. But when the boat is at the lake, it overheats. I?m guessing it has something to do with the backpressure.

Any help would be greatly appreciated.

Mike

 

[Chris1956]

Re: Mercury 150 Overheating

Mike, What year is the motor and what water pressure do you get? When you changed the water pump impeller, did you inspect the upper water pump cover for wear? How about the gaskets on the waterpump cover?

I guess the next step would be to inspect the cooling passages in the head and block for cloggs.

 

[mike-wright]

Re: Mercury 150 Overheating

Hi, The motor is A 1993 150 2.5L xri, I also used A new water pump cover and gaskets, at idle I have about 6psi at fullspeed I have about 13 psi, these are the same presure readings as when new. I also have a strong discharge at the water discharge(pee hole)

 

[j_martin]

Re: Mercury 150 Overheating

Hi, The motor is A 1993 150 2.5L xri, I also used A new water pump cover and gaskets, at idle I have about 6psi at fullspeed I have about 13 psi, these are the same presure readings as when new. I also have a strong discharge at the water discharge(pee hole)

I think 13 is a bit on the light side. Perhaps there's been a problem with the water pump discharge tube or it's seals all along.

 

[Shamus O'toole]

Re: Mercury 150 Overheating

Cooling passages in the heads...thats my guess.

 

[mike-wright]

Re: Mercury 150 Overheating

I was thinking that it might be the Cooling passages in the heads also, but the motor never heats up running of the garden hose, so to me that would mean the passages are good, I think

 

[Shamus O'toole]

Re: Mercury 150 Overheating

running on a hose the motors in nuetral and has no load on it. Cooling passages may be restricted and not fully blocked causing it to overheat while on a load.

 

[bryanwess2000]

Re: Mercury 150 Overheating

There's probably a better way to do this and the only reason I did this way is
because I basically got the motor for free. I flushed my v135 by pluging the
copper water tube, tilting the motor full up( as close to horizontal as possible)
then pulled the thermostats and poured vinegar/water 1:1 in until it was full. I
left it overnight then pulled the plug on the water tube and let all the water
and disolved mineral deposits drain in a garbage can. There was a ton of
sediment in the trash can after it settled and I could now see most of the
aluminum inside my heads. I poured about another 2 gallons of water through
the heads then installed my thermostats and lower unit and ran the motor
on the hose to flush it from the other direction.
DISCLAIMER: vinegar is acidic and can probably eat away at your rubber
seals, gaskets, and metal.

Plus if you have a piece of impeller or a pebble lodged somewhere this isn't
going to help

 

[mike-wright]

Re: Mercury 150 Overheating

if I run the motor in neutral on the garden hose it never over heats, if I run the boat in neutral at the lake it will over heat.

 

[CharlieB]

Re: Mercury 150 Overheating

Many things can cause overheating, retarded timing, leaking heat gaskets.

The fact that it overheats at IDLE in the lake and NOT at idle on the hose leads me to believe that you still have a problem with the water pump. Running pressures at WOT at only 13 also indicate a low flow from your water pump.

A new pump upper assy and impeller is not assurance that the pump is perfect yet. A warped lower pump half and/or a 'groove' worn into the stainless lower plate will not allow the impeller to seal perfectly to the lower plate, the warped lower housing can allow the pump to 'suck' air, reducing both cooling pressure and flow.

A weak seal between the lower pump housing and the gearcase can also allow air to suck in, not good for cooling.

Check again to be sure.