1990 200hp occasional overheating

[billm_usa1]

I;m retting occasional overheating when I run at more than 5000 RPM.
The pee stream is not strong 3psi at idle 10psi at 4500
Water pump was replaced this spring

At acceleration the water pressure will go from 3PSI up tp 20 then staedily drops back to 10PSI.

Could this be a stuck thermostat issue ?
Thanks

[SEAHORSE]

<table width="90%" cellspacing=0 cellpadding=0 align=center><tr><td>Quote, originally posted by billm_usa1 &raquo;</td></tr><tr><td class="quote">

At acceleration the water pressure will go from 3PSI up tp 20 then staedily drops back to 10PSI.

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Gotta find out what causes the loss of pressure at high speed.

some ideas:

exhaust leaking into water pump inlet area, usually under the plate

transducers, strakes, or thru-hulls within 14" of motor centerline causing aerated water

[billm_usa1]

Thanks for the reply
Your right about the exhaust leak.
Got the boat home this evening and on the muffs. - Very little water out the Pee tube - warm water out the prop exhaust.
Removed the thermostat housings and the thermostat and turned on the water and ran the motor. No water at either thermostat but I do get the initial oil smoke at startup coming out the thermostat seat.
Compression Check shows 100psi cold on each of the 6 cylinders. So I believe the head gaskets are ok.
The thermostat diaphram was still soft and pliable - no sign of heat stress. Also it wasn't wet.

Next move is to pull the lower unit then:
1&gt;Hook up the house water hose directly to the watertube and see if I can get water to the thermostat houisings and there are no blockages.
2&gt; New Upper and lower seals for the exhaust housing
3&gt; Reinstall the water pump plate and housing.

Last Night I put the water hose directly into the thermostat housings, water came out the relief holes at the water pump and the holes above the cavitation plate. So I believe there are no blockages in the system.

In another post you mention: You could try shotgunning approach such as replacing thermostats and taking apart and inspecting the 'blow off' valve and make sure the rubber grommet is glued into place. Use Loctite 380 for best results.
What is the "BLOW off" Valve and which rubber gromet are you refering to ?


Am I on the right track ?
Are there passages in the water jacket that could be blocked ?
Is there anything I need to watch out for ?&lt;br /&gt;&lt;br /&gt;
Modified by billm_usa1 at 6:45 AM 9/20/2010&lt;br /&gt;&lt;br /&gt;
Modified by billm_usa1 at 10:30 AM 9/20/2010


Modified by billm_usa1 at 8:43 AM 9/21/2010

[billm_usa1]

last night I pulled the lower unit and used the water hose on the water tube on the midsection. Water went through to the Thermostat housing. I disassembled the water pump to make sure that the lower unit wasn't plugged. I then watched an E-tec Video showing Impeller instalation. I discovered 2 seals had been left out the last two times that the Water Pump had been installed. The first is inside between the metal housing and the pump housing the second is to seal the pump to the water tube. Since both are on the pressure side I believe this has been a problem since I got the boat 2 years ago. Hope to have this back together with all the parts and on the lake Saturday.



Modified by billm_usa1 at 2:01 PM 9/23/2010

[SEAHORSE]

Those missing items definitely affect the water pressure. Be sure to install the complete factory water pump kit for best results, #5001594