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Last chance before I retire the motor

Old 06-14-2019, 01:54 AM
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Default Last chance before I retire the motor

I have a 2001 Mercury ELPTO 90 hp that has been rode hard and only broke down twice (one lower unit, one throttle connector). For the last 2 years it has had an intermittent overheat issue. I have replaced water pump, thermostat, poppet valve, took off water jacket (no obstruction) and yesterday removed the exhaust plate. There is some carbon on a couple of the bolts but no obvious gasket breakdown.

I'm going to replace the exhaust plate and divider gaskets but I'm out of ideas. Stream is good from tell tale, alarm cuts off after bringing back to idle, and stays off if I keep it at 3/4 throttle. It is NOT the low oil alarm.

Any thoughts? I'm concerned about the gasket under the powerhead but I'm not sure if that's worth going after.
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Old 06-14-2019, 03:04 AM
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If it only overheats at high throttle, then you have inadequate water supply, did you replace the complete water pump? or partial blockage in the water passages.
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Old 06-14-2019, 03:24 AM
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Originally Posted by noelm View Post
If it only overheats at high throttle, then you have inadequate water supply, did you replace the complete water pump? or partial blockage in the water passages.
I have suspected a partial blockage for some time but when I took the water jacket off there was almost no buildup on the walls or in the passages I could see, same with the exhaust plate. Pisses like a racehorse and I changed the impeller twice in the last 2 years.

EDIT: I did not replace the water pump housing but it looks fine.
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Old 06-14-2019, 04:14 AM
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temp sensor?
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Old 06-14-2019, 06:24 AM
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Originally Posted by rocksandblues View Post
temp sensor?
Maybe sensor is defective and increased water pressure is setting it off. ???
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Old 06-14-2019, 07:01 AM
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is it possible something else has changed to interfere with the water flow to the engine at high speeds, have you added anything like ,transducers or through hull strainer, has the hull developed some type of hook or rocker that is causing the flow to be disturbed...step back and look outside the box..
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Old 06-14-2019, 07:26 AM
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prop it down so as it cant reach the RPM that causes the alarm .
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Old 06-14-2019, 08:12 AM
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Originally Posted by rocksandblues View Post
temp sensor?
Easy to test sensor; remove and put in a pot of water on stove with thermometer to see what temperature it makes contact. You can also use an inexpensive IR thermometer to see if you have a "hot spot" on the head. You should also make sure stub hose connection between pump assembly and engine is sound/not leaking.
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Old 06-14-2019, 08:20 AM
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Run it in a barrel with 4 gallons of white vinegar mixed in the water.

For $10 it is worth a shot to clear a blockage.
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Old 06-14-2019, 10:25 AM
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You really need a water pressure gauge to test performance of the water pump system. "Pissing like a race horse" can be deceiving. A doubt a race horse develops 3 PSI at the "pisser" and 3 PSI will not cool your motor at speed. If you get enough wear in the bottom plate and top of the cup, the impeller will bypass enough water to give you low pressure.
The other place you can lose pressure is the bushings on the top and bottom of the water pipe going up to the power head.
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Old 06-14-2019, 10:32 AM
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Originally Posted by gfretwell View Post
You really need a water pressure gauge to test performance of the water pump system. "Pissing like a race horse" can be deceiving. A doubt a race horse develops 3 PSI at the "pisser" and 3 PSI will not cool your motor at speed. If you get enough wear in the bottom plate and top of the cup, the impeller will bypass enough water to give you low pressure.
The other place you can lose pressure is the bushings on the top and bottom of the water pipe going up to the power head.
Agreed knowing pressure is important

Originally Posted by fritz423 View Post
I have suspected a partial blockage for some time but when I took the water jacket off there was almost no buildup on the walls or in the passages I could see, same with the exhaust plate. Pisses like a racehorse and I changed the impeller twice in the last 2 years.

EDIT: I did not replace the water pump housing but it looks fine.
If it's anything like the larger water pumps I'd replace the housing also. IIRC a grooved plate can cause low pressure even with a new impeller.
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Old 06-14-2019, 10:41 AM
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When the alarm comes on have you put your hand in the stream to see if the water is actually that hot?
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Old 06-14-2019, 12:38 PM
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Originally Posted by beenie View Post
When the alarm comes on have you put your hand in the stream to see if the water is actually that hot?
It's never felt that hot but that water is bypassing the actual cooling system right? The tell tale originates at the top of the exhaust plate.

I wish my Merc manual had a water flow schematic...I don't really understand which direction the flow goes.
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Old 06-14-2019, 12:40 PM
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Originally Posted by amcfall View Post
Agreed knowing pressure is important



If it's anything like the larger water pumps I'd replace the housing also. IIRC a grooved plate can cause low pressure even with a new impeller.
I think I will replace the water pump housing: even if I give up and buy a new boat/motor (more and more likely) I'd like to give the boat and motor to my son as a "starter boat".

EDIT: I'm an idiot. The water pump housing was new in 2017 when I replaced lower unit with a rebuilt. Guess I'll be testing marineengine.com's new return policy...

Last edited by fritz423; 06-14-2019 at 01:15 PM.
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Old 06-14-2019, 12:57 PM
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The pee stream is before the water gets to the block on every motor I have worked on. It comes straight from the raw water manifold although it may go through the ECM or fuel cooler. It is no indication of the block temperature. See how long you can hold your finger on the thermostat housing. If it is a second or so you are in the 130 range (Mc Donalds coffee hot) and if you get a blister when you touch it, turn the motor off with your good hand..
You can try backflushing the block through the thermostat hole with the foot dropped if you have good water pressure and still running hot. A short piece of swim noodle on the end of the hose makes a good tool for that. The hose end shut off makes it a little drier while you are getting the noodle seated.

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Old 06-14-2019, 12:59 PM
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Originally Posted by fritz423 View Post
I have a 2001 Mercury ELPTO 90 hp that has been rode hard and only broke down twice (one lower unit, one throttle connector). For the last 2 years it has had an intermittent overheat issue. I have replaced water pump, thermostat, poppet valve, took off water jacket (no obstruction) and yesterday removed the exhaust plate. There is some carbon on a couple of the bolts but no obvious gasket breakdown.

I'm going to replace the exhaust plate and divider gaskets but I'm out of ideas. Stream is good from tell tale, alarm cuts off after bringing back to idle, and stays off if I keep it at 3/4 throttle. It is NOT the low oil alarm.

Any thoughts? I'm concerned about the gasket under the powerhead but I'm not sure if that's worth going after.
Wouldn't it technically now be three times it broken down?
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Old 06-14-2019, 01:11 PM
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Originally Posted by fishingfun View Post
Wouldn't it technically now be three times it broken down?
I ran it all last week like this. I just had to keep it off WOT. I'm about to the point where if it dies-good riddance.
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Old 06-14-2019, 01:13 PM
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Originally Posted by gfretwell View Post
You really need a water pressure gauge to test performance of the water pump system. "Pissing like a race horse" can be deceiving. A doubt a race horse develops 3 PSI at the "pisser" and 3 PSI will not cool your motor at speed. If you get enough wear in the bottom plate and top of the cup, the impeller will bypass enough water to give you low pressure.
The other place you can lose pressure is the bushings on the top and bottom of the water pipe going up to the power head.
Where would you test water pressure and how? Do you test at idle?
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Old 06-14-2019, 01:16 PM
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Originally Posted by gfretwell View Post
The pee stream is before the water gets to the block on every motor I have worked on. It comes straight from the raw water manifold although it may go through the ECM or fuel cooler. It is no indication of the block temperature. See how long you can hold your finger on the thermostat housing. If it is a second or so you are in the 130 range (Mc Donalds coffee hot) and if you get a blister when you touch it, turn the motor off with your good hand..
You can try backflushing the block through the thermostat hole with the foot dropped if you have good water pressure and still running hot. A short piece of swim noodle on the end of the hose makes a good tool for that. The hose end shut off makes it a little drier while you are getting the noodle seated.

Attachment 1100857
I will do this when I take the lower unit off (again) to check the impeller and housing.
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Old 06-14-2019, 01:34 PM
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I had a 2000 135 Optimax that I struggled with for years for over temp/guardian mode(1200 rpm). Spent a ton on everything temp related - even had the "special" Merc aftermarket water bypass kit installed. Three dealers/mechanics - still the damn buzzer when you least needed it - in the inlet coming in on outgoing tide etc. Went to pick it up from service about a month ago: " changed water pump/saw nothing wrong/runs ok on hose etc". Told the yard guy to put it back - I didn't want to take it home. Went up front and sat down with the head guy and asked what he had to remedy the problem. " I have a 150 Merc four stroke that would be great on your boat." Two weeks later I am back on the water with a brand new motor. Other than the 20 hour break in procedure I am absolutely thrilled. Like a brand new boat. Wouldn't you know it my wife says "I don't know why you didn't do it years ago". If interested the boat is a 2003 1900 Maycraft CC. Best of luck with your motor but after 12 years I gave up.
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