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J90PLSOA Overcooling

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BillonAdvent2

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J90PLOA - I bought this engine about two months ago. Starts fine. QuickStart keeps engine at 1500 RPM for about six minutes. Then at a temperature of 80 degrees QuickStart disengages and engine drops back to 900 RPM. Immediately the temperature starts going up, and in two minutes the temp is 140 degrees, where it stabilizes. Increase to 1200 RPM for five minutes, temp 140 degrees. Increase to 1500 RPM for five minutes , temp drops to 90 degrees. Increase to 2000 RPM for five minutes, temp 80 degrees. Increase to 4000RPM for five minutes, temp 70 degrees. When I slow down to dock, QuickStart has reactivated, engine running at 1500 RPM. It seems to me that the thermostats are working properly up to 1500 RPM, then excess pressure from the pump opens the pressure relief, introducing cold water and cooling the engine down. New thermostats and springs with no change in symptoms. Thermostat housings are clean and the seats good. Temp readings are an average of four, thermostat housing and top of engine block, both sides. Water temperature 55 degrees. What could cause excess pressure in the cooling water?
 
Sounds like stats are not seated correctly. Only reading you should be concerned about is at the stat housing as block will be cooler..
 
faztbullet said:
Sounds like stats are not seated correctly. Only reading you should be concerned about is at the stat housing as block will be cooler..
Click to expand...
After the FastStart drops back and RPMs are 900 the temperature rises nicely to 140 degrees and stays there. That tells me that the stats start out properly seated, and work properly, but lift at about 1500 RPMs. Is there a way to verify that the thermostats are seated properly? The seats look good. Is there any trick to installing the thermostats? I just stick them in and make sure that the springs are centered, then tighten to 130 "#.
 
faztbullet said:
Sounds like stats are not seated correctly. Only reading you should be concerned about is at the stat housing as block will be cooler..
Click to expand...
As long as the temperature is "normal" about 140 degrees at low RPMs, the thermostat housing is 3 to 7 degrees warmer than the block. At higher RPMs when the temps are in the 80s, 70s and 60s the block is 1 to 4 degrees warmer than the thermostat hosing.
 
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