Motor overheating

I have a 1967 Merc 200 that hasn't been started in 40 something years, and I replaced the impeller, spark plugs, and a few other stuff. I got it running the other day and it was running fine until the top started smoking white smoke. I took the cover off and the fuel tank had burned through the brown plastic that is inside the cover. It runs just fine for a few minutes, but then starts smoking a little bit in the top. I think it might just be burning off old grease that's been caked up inside for years. I have the correct oil to gas ratio, and seafoam running through it as well. Any idea why the fuel tank is too hot?

And by fuel tank I'm referring to the tank inside the motor itself, not the actual fuel can.

Is it pumping water out the telltale?

I can't seem to find where the telltale is located

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Originally Posted by OutdoorWilly

I can't seem to find where the telltale is located

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when your motor is running it should have a little stream of water coming out the side of the motor if not it sounds like your impeller in not working correctly!!!!

yes but I can't seem to find anywhere where it can come out, unless it is supposed to come out of the exhaust holes

maybe this will HELP!!!!!

1967 Mercury 200 (20hp) - YouTube

His has a hole for it to pee out of. I have the exact same motor, but the hole is not there. It is very strange.

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Originally Posted by OutdoorWilly

His has a hole for it to pee out of. I have the exact same motor, but the hole is not there. It is very strange.

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double check and make sure a mud dobber ain't plugged up the hole!!!!

Haha I have checked and checked, cleaned everything I can possibly clean, and still can't find anywhere for the water to come out of. I don't know why I can't find this dadgum hole. The water might have to come out of the exhaust holes, but it doesn't. I don't think I put the impeller in incorrectly, but water is just not getting up there.

saw a thread similar to this a while back, and the pee hole was above the prop "under" the cavitation plate if I remember right.

Take the cowling off and look inside the edge of the housing on the motor for anything that resembles a hose/tube attached to the inside of the motor pointing to the outside of the engine. That would be the pee tube and there WILL be a hole plugged by dirt dobbers and you will have to open that hole up. Has to have a place up there for the water to excape quickly from the cooling system that sends water through the upper end. Good luck, when you think you have looked at everything look again, there is one there. Ferdi

Dang it, I'm showing my age. Never knew there was a 200merc made in the 1960's. lol

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Originally Posted by slimeyslab

Dang it, I'm showing my age. Never knew there was a 200merc made in the 1960's. lol

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its actually a 20hp motor,back then mercury would have 100=10hp,500=50hp and so on!!!

Haha I sure wish this thing was a lot smaller...maybe 10hp or less. It's difficult to move it back and forth when it's so heavy.

A lot of those older motors didn't have a tell tale but if you knew where to drill you could put one in. I was going to suggest thermostat but according to the manual you don't have one of those either. I would revisit the impeller.

Did the impeller come apart? Did you find the pieces? Is the tube to motor plugged if this motor had one? Had this happen tube had a sharp bend in it and pieces where stuck there.

What if I disconnected the hose on the engine block and ran water down there?
Also, I don't know where the hose runs to. It looks as if it runs down to the lower unit and I guess the impeller somehow.

So if there is no telltale, then is there any other way to know if it is running properly?

Quote:

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Originally Posted by OutdoorWilly

I have a 1967 Merc 200 that hasn't been started in 40 something years, and I replaced the impeller, spark plugs, and a few other stuff. I got it running the other day and it was running fine until the top started smoking white smoke. I took the cover off and the fuel tank had burned through the brown plastic that is inside the cover. It runs just fine for a few minutes, but then starts smoking a little bit in the top. I think it might just be burning off old grease that's been caked up inside for years. I have the correct oil to gas ratio, and seafoam running through it as well. Any idea why the fuel tank is too hot?

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White smoke is likely steam. There is either a hole in the water jacket (since your motor has no cylinder head), or a bad exhaust cover gasket.
I don't understand the "fuel tank is hot" statement. What tank is inside the motor?
When you changed the impeller, did you get the pin back in the driveshaft that catches on the impeller and spins it?
If you wanted, you could remove the lower unit and use some duct tape to attach the water hose to it. However, don't turn the hose on wide open or it will possibly cause problems. I'd think your tattle tale is coming out the bottom cowl/belly pan of your motor. You didn't see a hose running off the top or side of the cylinder head that was going down to the lower cowl? If not, the tattle tale may come from about an 1/8" diameter hole that goes through the belly pan from a hole in the bottom edge of the power head. Keep searching, as I'm almost positive it has one. It could easily be stopped up by a dirt dauber or something else and a lot of times you'll see steam coming from it when the exhaust gasket seals are bad, or if exhaust gases are coming into the system via the intake main water tube gaskets coming into or going out of the water pump.

Yes, there is a hose that goes down to the belly pan of my motor, but there is no hole on the outside of the belly pan.

willy, i would say take the motor to a mercury mechanic and let them fix it before you heat the motor to the point of ruining it. i know you don't want to spend the money but i believe it's that or you will be looking for another motor.

Archerguy is the one to ask, but it sounds like the powerhead is plugged up with something. If archerguy doesn't answer take it somewhere before its too late...

It's really very simple. Take the lower unit off and spin the drive shaft with a 1/2" drill with the lower unit SUBMERGED in water. If water shoots out the water tube coming out of the pump then the problem lies elsewhere. If you get some tape and attach a water hose to the copper water tube that goes up to the powerhead and the cylinder heads stay cool with it running, then the indicator hole/tube is stopped up. If you have a hose running from the side, top, or back of the cylinder head going to the belly pan then detach it. Take the hose off the powerhead and see if water will go through it. If so, then see if water will go through the nipple that the hose attaches to. If not, uplug it with a piece of weedeater string or wire. Make sure you're not mistaking the water tube for an oil line that goes from the carb to the side of the crankcase.

Actually, if one can't handle getting the water flowing through the powerhead, the advice to take it to a real outboard mechanic is the best. Sadly, there aren't a lot of guys willing to work on an engine that old, and there are also very few competent mercury mechanics out there. iboats.com is a good place to ask these questions in the mercury/mariner forum. I would almost bet that your driveshaft is rusted/pitted, and the lower unit is worthless on that motor. There must be a million of those with good powerheads and bad lower units. You might keep that in mind before you take it to a mechanic. I personally don't think it will be worth the money to take it to one due to the high cost of ignition parts and lower unit/driveshaft parts, and due to the high cost of time and labor involved. I wouldn't even consider working on a merc of that vintage for someone. Unless it is totally gone through(new wiring, lower unit seals and driveshaft/propshaft speedisleeves, carb cleaning, fuel line replacement, etc.) it will undoubtedly break down on you and you wouldn't be satisfied. The cost of the aforementioned work/parts would put you in the price range of a much newer used engine.
JMO,
JBJ

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Originally Posted by OutdoorWilly

I have a 1967 Merc 200 that hasn't been started in 40 something years, and I replaced the impeller, spark plugs, and a few other stuff. I got it running the other day and it was running fine until the top started smoking white smoke. I took the cover off and the fuel tank had burned through the brown plastic that is inside the cover. It runs just fine for a few minutes, but then starts smoking a little bit in the top. I think it might just be burning off old grease that's been caked up inside for years. I have the correct oil to gas ratio, and seafoam running through it as well. Any idea why the fuel tank is too hot?

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The powerhead should never get more than 140-160 degrees, which isn't hot enough to burn anything. It's overheating as already stated, because no water is going through the powerhead. You have likely already caused some major piston scuffing.
A 60's and 70's merc 200 is not the best motor to start learning on. Your best be would be to sell it or part it out. At the very least, check compression and make sure all cylinders are even. And pull the lower unit oil drain plug and see how much water is in there. If it's full of water, scrap the motor.
JMO,
JBJ

Hey Willy did you ever get the problem taken care of on your motor? If so what was it? Ferdi aka Fred

No I tried to stick a clothes hanger or some copper wire down the hose from the top to see if it would un-clog any dirt or anything, but the wire stops a few inches down. It's hitting metal and not letting it go through the rest of the hose. I tried to pour water down the hose from the top, but it only fills up a few inches and then overflows. It's very strange. At this point I think I'll just have to take the lower unit back off, even though it took days for me to figure out how to get it off and back on when I first did it over the summer.

"At this point I think I'll just have to take the lower unit back off, even though it took days for me to figure out how to get it off and back on when I first did it over the summer. "


it's always easier the second time and the third. don't ask how I know that.:banghead

Did you check the impellor to make sure it is working? I have done this and seen others do it, pretty sure your impellor slides down into the water pump housing, problem is there is a very small key way that stands against the drive shaft and you have to shove the impellor down into the housing and not knock the key over.........good luck I fight these all the time. The way I do it is use a glue for weather strips on auto's, yellow dries fast I glue the key onto the slot in the drive shaft and use a pair of needle nose vise grips to lock it in place until it dries overnight. them put vasoline on the inpellor and kind of fold it up in your finger while lining up the slot in the impellor with the key glued to the drive shaft. Work it down into the housing until it bottoms out, the turn the drive shaft by hand and try to keep the impellor from turning, if the key is in place the impellor will turn when the drive shaft is turned, if key falls down impellor will let drve shaft tun inside of it, other think to check is the rubber gromet on top of the water pump housing, if it gets pushed down or folded over it will restrict the water flow up the brass tube to the powerhead causing the motor to over heat. Look at these things and if everything is ok you may need to find someone near you who works on the oldies as those guy's are becoming fewer and fewer