2000 Merc 200 EFI getting hot

I did my normal replace the water pump impeller as I do every 2-3 years. It was not getting too hot but increasing temp at mid range throttle, fine at idle or WOT. It was showing wear so I put the "kit" in. Now it is fine at idle, ok at mid range but gets hot at WOT????? No idea if I need a thermostat or heaven forbid I put it back together wrong.....or ???? Deciding where to start or if I need to turn it over to a professional? After 5 heart procedures, cancer surgery and radiation in the past 3 years, not sure I am strong enough to tackle a big project. Thanks for guidance

I'm not sure about your Mercury EFI engine, but it still could be something relatively simple. If it is peeing after the engine warms up and the water pressure increases as RPM increases, that's a good start. It could also be that the tube from the lower unit to the engine didn't get lined up correctly, so not all water is getting into the water passages in the cylinder head, since you just changed the impeller.

A couple of years ago I had overheating on my '85 Evinrude XP150 at only WOT despite a new impeller, thermostats, and pressure relief valves and springs. The issue ended up being little rubber diverter tubes in the water passages in the engine block had swollen after nearly 40 years and needed to be replaced with fresh tubes, and I could see it plain as day as soon as I pulled the cylinder heads. After changing the tubes, installing new gaskets, and properly torquing the cylinder head bots, it's been fine.

I have to ask this, did you turn the driveshaft clockwise while pushing the Impeller housing down? Also did you lubricate the new impeller and housing so it wouldn't snag? The Output Seal & Sleeve may not have seated properly also. I troubleshooted for many years and Human Intervention was always in my mind during investigating failures. Once in the North Sea I had a English Mechanic who had apprenticed in EMD Diesel Engines serviced one on the 20cyl Turbocharged EMD Generator engines. I was not the Chief Engineer on that Vessel but the Electrician (all electric vessel). So I couldn't listen to the wining from the Mechanic that the Scavenger Pump just happened to fail right after servicing. See EMD engines have a Oil Strainer Box in the front and if you install the Strainers upside down the Scavenger pump sucks air, will not prime. The way to test is with a 5 gallon bucket of oil, you remove the lid of the Strainer Box, start the engine, and dump the entire 5 gallon bucket of oil in flooding the box sealing up the air leaks. As soon as I did the oil PSI shot up to 80 pounds. Moral of the story is I usually find a related problem to recent human intervention in the reassembly, even my own reassemblies.

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Originally Posted by Rojo

I have to ask this, did you turn the driveshaft clockwise while pushing the Impeller housing down? Also did you lubricate the new impeller and housing so it wouldn't snag? The Output Seal & Sleeve may not have seated properly also. I troubleshooted for many years and Human Intervention was always in my mind during investigating failures. Once in the North Sea I had a English Mechanic who had apprenticed in EMD Diesel Engines serviced one on the 20cyl Turbocharged EMD Generator engines. I was not the Chief Engineer on that Vessel but the Electrician (all electric vessel). So I couldn't listen to the wining from the Mechanic that the Scavenger Pump just happened to fail right after servicing. See EMD engines have a Oil Strainer Box in the front and if you install the Strainers upside down the Scavenger pump sucks air, will not prime. The way to test is with a 5 gallon bucket of oil, you remove the lid of the Strainer Box, start the engine, and dump the entire 5 gallon bucket of oil in flooding the box sealing up the air leaks. As soon as I did the oil PSI shot up to 80 pounds. Moral of the story is I usually find a related problem to recent human intervention in the reassembly, even my own reassemblies.

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Thanks, you are wise to suspect human error, unfortunately I agree. I am by no means a tech, but have replaced many impellers. I always try to be very careful but since cancer surgery, radiation, 4 heart procedures, including quadruple bypass in the past 2.5 years my mind has slipped a bit, and I am doubting I am physically capable at this point to tear it down again. Will likely get the checkbook out and pray that I have not made too big of a mess for the professionals.

I mentioned Rojo's post to my wife....she said "if you remember when you put it together you said "never had one go together so easy, nothing is easy for me these days" appears I may have been correct.

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Originally Posted by grizwilson

Thanks, you are wise to suspect human error, unfortunately I agree. I am by no means a tech, but have replaced many impellers. I always try to be very careful but since cancer surgery, radiation, 4 heart procedures, including quadruple bypass in the past 2.5 years my mind has slipped a bit, and I am doubting I am physically capable at this point to tear it down again. Will likely get the checkbook out and pray that I have not made too big of a mess for the professionals.

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Can't be that big of a deal. Shouldn't cost any more than a Water Pump job. Labor hours are the same. I'm confident the new parts are fine. Do you remember putting the key back in between the Driveshaft & Impeller?

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Originally Posted by Rojo

Can't be that big of a deal. Shouldn't cost any more than a Water Pump job. Labor hours are the same. I'm confident the new parts are fine. Do you remember putting the key back in between the Driveshaft & Impeller?

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Thanks, yeah I am sure I put the key in, it works fine at idle and low speed. One thought that frightens me is the water pressure popoff valve or its diaphragm??? Or possibly the thermostat is not opening all the way so too restricted at WOT It is possible that the output seal possibly did not seat properly I may get brave and pull it a part this week, ......

Ok, to reason it thru you were doing a PM not dealing with a failure so the Thermostat hasn't been touched. I assume you have temperature probe in the block and a gauge on the dash, is that correct? Do you have a water pressure gauge? The By-Pass shouldn't be open unless the Thermostat is closed and your RPM's are high enough turning the Impeller creating enough water pressure to open it. Kinda goes against the Lack of Water flow theory. I had ask earlier do you remember turning the driveshaft while pressing down on the Impeller housing? If you read my post on the 40 Merc of mine I serviced the other day 2 blades of the Impeller was turned the opposite way and one was completely folded in half. Whoever installed that Impeller didn't turn the Driveshaft when installing the Impeller housing. V-6 Foots can get heavy when stabbing the Driveshaft Splines into the Crankshaft. If you do decide to pull the Gearcase maybe line up a extra pair of hands to stab it back.

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Originally Posted by Rojo

Ok, to reason it thru you were doing a PM not dealing with a failure so the Thermostat hasn't been touched. I assume you have temperature probe in the block and a gauge on the dash, is that correct? Do you have a water pressure gauge? The By-Pass shouldn't be open unless the Thermostat is closed and your RPM's are high enough turning the Impeller creating enough water pressure to open it. Kinda goes against the Lack of Water flow theory. I had ask earlier do you remember turning the driveshaft while pressing down on the Impeller housing? If you read my post on the 40 Merc of mine I serviced the other day 2 blades of the Impeller was turned the opposite way and one was completely folded in half. Whoever installed that Impeller didn't turn the Driveshaft when installing the Impeller housing. V-6 Foots can get heavy when stabbing the Driveshaft Splines into the Crankshaft. If you do decide to pull the Gearcase maybe line up a extra pair of hands to stab it back.

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Thanks, I do have a temp gauge in dash, no water pressure gauge, just look to make sure it is peeing. I usually do not turn the shaft, but rather slide the housing down and fold the "ears" in one at a time.... could have fat fingered it. ??? You are correct in your reasoning, as before, as in years past, the impeller gets "set" works fine at idle and WOT but warms in low throttle..... that was what I was attempting to correct. This one is throwing me. My neighbor who normally helps had hand surgery, I know better than involve my wife of 47 years........Thanks plan on giving a go

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Originally Posted by grizwilson

Thanks, I do have a temp gauge in dash, no water pressure gauge, just look to make sure it is peeing. I usually do not turn the shaft, but rather slide the housing down and fold the "ears" in one at a time.... could have fat fingered it. ??? You are correct in your reasoning, as before, as in years past, the impeller gets "set" works fine at idle and WOT but warms in low throttle..... that was what I was attempting to correct. This one is throwing me. My neighbor who normally helps had hand surgery, I know better than involve my wife of 47 years........Thanks plan on giving a go

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Your response is saying the by-pass is leaking. Another little story. Not naming names but the biggest Yamaha repair around had my Bud's boat for engine overheating at idle speeds. Well on a Yamaha F250 4 Stroke 2005 model the Poppit Valve is a different part number than previous years and later years. There is a small window which the 2005 model is inside of that you install a OEM Poppit Valve that has a tighter spring. It's a Real Pain to load a 30ft+ boat on the trailer, a boat too tall to even pull out of your subdivision, you have to drive it 30 minutes away to load it, but bring it to this big Yamaha shop only to have them install the wrong Poppit Valve so they didn't fix a thing. I went to the customers house, took pictures of the tags on the engine, looked up the correct OEM part numbers, ordered the parts online from a Yamaha Dealer, installed the parts in both engines (Twins) so we don't have to do the other engine 6 months later. That's 8 years ago, no more cooling problems at idle.

You do have to follow some assembly practices to the letter as well as use the correct parts.