1994 88 SPL overheat alarm at WOT

Lloydhess

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Apr 27, 2025
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Recently just bought this boat with a 1994 evinrude 88 SPL. Motor was only ran maybe a week out of the year. Owner before me just recently had a water pump put on it back in February and ran it one time since then. Within the week I have owned it I noticed everytime it goes anything above 4500 RPM or wide open throttle the over heat alarm sounds. I replaced the thermostats they were broken in half. New poppet valves and it still did it. You can cruise all day 4500 or below and it does fine. I did narrow it down to the port side head throwing the alarm. Unplugged the sensor and it goes away. I have not actually checked the temperature of it when it does it. But I can cut it off and let it sit about 30-45 seconds and fire it back up and it doesn’t come back on again till wide open. Any suggestions on what else to check? I was considering running Rydlyme through it to see if that would help before I pulled the heads off. Thanks!
 

cyclops222

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Mar 21, 2024
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How can 2 thermostats be broken ? Idiot DIY is only possibility. Broken pieces of a old water pump blades stuck in the motor can cause that condition every time.
 

racerone

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Dec 28, 2013
Messages
38,481
Possibly the water diverters are blocking water flow on one side.----Cylinder head must be removed to inspect those 2 items.----And these motors have a history of broken piston rings.----Do a compression test.---Keep the values for future reference.----Post them here.
 

Lloydhess

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Apr 27, 2025
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How can 2 thermostats be broken ? Idiot DIY is only possibility. Broken pieces of an old water pump blades stuck in the motor can cause that condition every time.
This is how both came out. Wax pellet was stuck in the housing actual spring and housing was stuck in the block. Could be due to corrosion. I was thinking about doing a rydlime flush on it and go from there. If that doesn’t work then I’ll pull the heads.
 

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Crosbyman

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see conclusion to a long story and... ridlyme...
 

Lloydhess

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Apr 27, 2025
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I was also leaning towards the hoses coming off the heads to the thermostat housing. They both a serious kink in the bend of the elbow. Obviously a restriction in itself being they’re almost flat in the bend and very soft and pliable. I ordered two new ones but they haven’t arrived yet. I figured I would try that if that doesn’t make a difference then rydlyme and pull the heads and replace the flow diverters. I live close to the marina so obtaining parts are not an issue.
 

Lloydhess

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Apr 27, 2025
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IMG_0870.jpegBingo! New parts are on order. What do you recommend using to clean the mating surfaces ? Scotchbrite on a whiz wheel? I’m a forklift mechanic so have necessary tools to do repairs. Thanks.
 

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racerone

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Dec 28, 2013
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The cylinder heads are warped.----Need to refinish them before installing new head gaskets.
 

Lloydhess

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Apr 27, 2025
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Is any copper gasket spray recommend for these head gaskets? In the manual it says something about using J/E gasket sealing compound. Don’t want to jinx myself with what I would normally do.
Possibly the water diverters are blocking water flow on one side.----Cylinder head must be removed to inspect those 2 items.----And these motors have a history of broken piston rings.----Do a compression test.---Keep the values for future reference.----Post them here.
compression was 120PSI across the board.
 
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