Steam? Exhaust? Normal?

[dOb]

My motor is a 1974 Mercury 500 Thunderbolt 50hp.
Last weekend I took my family out to cruise around the lake and look at ducks and whatnot. Anyway, we were out for about an hour and a half total. It was about 55 with sunshine and a little windier than I would have liked. About 20 minutes in, I noticed this steam/exhaust coming from around the motor. I figured, hot motor, cold water, no big deal. Like I said, we cruised around for about an hour and a half. It never showed signs of stress. My wife thought it was odd, so I shot this video. We actually finished up the day going WOT back to the ramp to see what kind of speed we could get.

We managed 27mph, that?s normal for this set up and 5 people with some wind. I didn?t think much about the steam until I got home and started reading horror stories here about overheating. I don?t want to be over paranoid, but I also don?t want to fry my motor.

This video is the motor running at about 2000 rpms. The stream from the tell tale was pretty steady all day, it just doesn?t show on the video. What do you think?

 

[dOb]

Re: Steam? Exhaust? Normal?

OK, here's an update - After reading many posts about overheating, I still couldn't be sure if this was overheating, or just normal behavior. So I did some investigating. I removed the lower unit and checked for blockage. Even though I knew I had seen a stream all day, I thought that maybe I wasn't getting enough circulation. No blockage, but I did find that the impeller had lost a couple of fins. I replaced the impeller and went out today.
I still had a steady pee stream, and still had steam. Not as much steam, but it was a warmer day. I noticed that the pee stream was warm, not hot, at first. I rode a while WOT, and then checked again. This time the pee stream was uncomfortably hot. I idled for less than five minutes, and it went back down to warm, not hot at all.

Questions: I figure that small motors get hot when running wide open, but with out a thermostat, how do I avoid doing damage when the temp is triple digits and the water is much warmer?
And also, Is there any way to check that I am getting good circulation of water? I have a steady stream, but it isn't super strong. I think that at one time this was a salt water boat. Could that have an impact?

Thanks

 

[CharlieB]

Re: Steam? Exhaust? Normal?

You mentioned the old impeller had lost a couple of fins, did you FIND and REMOVE them?

If not, they are still inside the motor somewhere, restricting water flow.

Go get them.

Start with the exhaust side cover, NOTE: Be CAREFUL removing those bolts, they have a nasty habit of sticking and breaking off if you just put a wrench on them and muscle them. Give each bolt head a couple 'Love Taps' with a ball peen to get its attention, let them know you are serious, and hopefully to start to loosen any corrosion around their threads.

 

[dOb]

Re: Steam? Exhaust? Normal?

You mentioned the old impeller had lost a couple of fins, did you FIND and REMOVE them?

Yep. I found all of the pieces. I could see where they fit back on the old impeller. It was all there.

What am I looking for when I remove the exhaust side cover?

 

[Chris1956]

Re: Steam? Exhaust? Normal?

That motor should run dead cold at idle warmer at speed. Put your hand on the exhaust cover (port side, long cover) and feel it when cruising. It should not get more than warm.

When you replaced the impeller, did you replace the wearplate and gaskets? Did you inspect the upper waterpump cover? If not, the new impeller may not be pumping to capacity, which is real important.

 

[dOb]

Re: Steam? Exhaust? Normal?

I'll check the exhaust cover. Is this something I can check running on muffs?

The gaskets were replaced last summer, and seemed to be in good condition, so I didn't replace them.. Also, I cleaned off the water pump cover (plastic cover with metal cup that fits over the impeller?) and didn't see anything unusual. Is it possible to over-tighten the cover and restrict the impeller?

 

[Texasmark]

Re: Steam? Exhaust? Normal?

Since this is a pre "New Merc" engine design, you don't have a tstat so any steam is a problem. If you had a stat steam could be had at cold ambient temps.

Mark

 

[dOb]

Re: Steam? Exhaust? Normal?

I’m going to try everything I can before trying to remove the exhaust cover. I am concerned about pulling the powerhead and broken bolts and what not.
I tried running weed eater line through every water passage I could reach. I took the water pump apart checked for anything unusual. I pulled the water pump base out to see if there was any thing obvious, and didn’t see anything. I ran it on muffs and unscrewed the little brass screw on the cover between the plugs. Water poured out, so I figure it is circulating.

I went out fishing yesterday with the same results as before. I have water at the tell-tale, but it still gets uncomfortably hot. I’m wondering if I just don’t have enough pressure from the pump. Is there any chance that replacing the water pump base, gaskets and top, would help? Also, would I be able to “see” if there was a problem with the old one, or do they just wear out?

 

[CharlieB]

Re: Steam? Exhaust? Normal?

If you look closely at the side of an impeller you will notice a raised 'ring' that presses against the stainless parts, sealing the impeller sides.

Now look at those stainless parts, the 'cup' and lower 'plate', if they show a 'ring' worn into the metal then that raise portion on the impeller will no longer seal properly and it is time to order a water pump rebuild 'kit' and replace this stainless parts.

Testing water flow while on the hose can be misleading as the water pressure of the hose will 'assist' the water pump, falsely increasing both pressure and flow above that once the boat is launched.

Running in a barrel will provide a much more realistic flow test than the hose.

 

[dOb]

Re: Steam? Exhaust? Normal?

Thanks for advice. I went ahead and ordered a new water pump kit. Top, bottom, gaskets, plate, the whole thing. I replaced everything just like the old one was. I took it to the lake this morning, and had the same results. The stream is a little stronger (maybe) but the stream and the motor are getting too hot to touch.
So now I have two questions;
1. I know that the pump kits cover several years of pumps, so they always have extra gaskets. I replaced everything just like the old pump, but along with the gaskets, I did have a couple of O-rings left over. One about the size of an Oreo cookie, and the other about the size of a nickel. There was another large O-ring that went on the bottom of the pump. Does anyone with this motor know if these other two o-rings have a home? I didn?t see anything in the service manual that I could tell.
2. Is it possible to remove the exhaust cover with out pulling the power head?

BTW ? I agree about the muffs not being a good indication of operation. But I get just the opposite results. I have a much stronger stream when I?m in the lake. At home I have to run a really long hose and it?s uphill.

Thanks

 

[CharlieB]

Re: Steam? Exhaust? Normal?

With the exhaust cover removed you can look into the water passages to find any obstruction, same with the cyl cover (instead of a cyl head). A restriction of the outlet is just as bad as one on the inlet side, either reduce cooling flow.
Both covers should be able to be removed without pulling the powerhead, it can be awkward.

Your biggest problem will be NOT breaking off bolts that have been stuck in there for a long time. Use LOTS of penetrating oil, like PB Blaster, or Kroil. Vibration helps break corrosion, just do NOT put a wrench on and forcefull turn, that's almost a certainty many will break off. Patience, heat, light hammer taps, and time, and every one should give up and turn.

You may find slivers of a rotted log you never knew you had hit.

 

[Chris1956]

Re: Steam? Exhaust? Normal?

My old IL6 developed a crushed water tube(old timers blamed salt buildup), where is entered the exhaust extension casting at the base of the powerhead. It also eventually rotted away, so I had to solder on a new 1/2" copper piece.

Pretty obscure damage, but it did happen....

 

[dOb]

Re: Steam? Exhaust? Normal?

I have considered that the problem may be at the connection of the water tube and the power head. I'll just keep eliminating things for now. Hopefully this latest fix will do the trick.


After a couple of days of banging, heating and soaking with penetrating oil, I decided to give it my best last night. I only broke three bolt heads. Luckily they were all on the cylinder cover and those are nut and bolt combinations, so I can replace those. The cylinder cover isn?t threaded. The exhaust cover came off with all of the bolts in tact. I used a pencil torch to heat up the bolt heads. That way I didn?t have to worry about a heat shield and cooking the engine and fuel lines.

I didn?t see any real obvious obstruction. But there is a lot of dried up gasket material blocking the channels on the side of the exhaust cover, and some sandy crumbly stuff in one corner. I?ve ordered the gaskets and won?t get a chance to get them on until maybe Saturday morning or Sunday afternoon.

Questions:
1. I plan on using a wire brush to clean these off. Is there a better way to remove all of the old gasket material and grime build up?

2. I also noticed these small cracks in the inner exhaust plate. You can see light through them. Are these a big deal? Can I fill the cracks with some JB Weld and be done with it?

Thanks again

 

[Chris1956]

Re: Steam? Exhaust? Normal?

I cannot see your pictures. If there are cracks in the exhaust baffle #19 in the following URl, you need to replace it. Dittio if the cracks are in #32.

http://www.crowleymarine.com/mercury-outboard/parts/449_13.cfm

 

[dOb]

Re: Steam? Exhaust? Normal?

I cannot see your pictures. If there are cracks in the exhaust baffle #19 in the following URl, you need to replace it. Dittio if the cracks are in #32.

http://www.crowleymarine.com/mercury-outboard/parts/449_13.cfm

I believe it would be #19 the PLATE-BAFFLE. I wonder why the pics aren't showing? There are two hairline cracks. Less than an inch each. I don't mean to second guess your advice, I appreciate the help. And I don't really want to be back in here anytime soon, but it seems like this is the kind of thing that JB Weld was made for. Am I just being too optimistic?

 

[CharlieB]

Re: Steam? Exhaust? Normal?

Pics show fine for me.

These cracks will allow water to spray into the exhaust ports at some speeds, steam cleaning the piston, while at higher exhaust pressures can allow exhaust to blow into the cooling system, displacing cooling water and over-heating the motor.

You have found your problem, now repair it correctly.

JD Weld is NOT and approved repair, I would NOT risk an over-heat and possible engine distruction on a chemical fix. Nor would I recommend TIG welding, the material is too contaminated and extremely difficult to prepare an absolutely clean surfaces for welding.

Tho if the part is NLA, I would sooner see it TIG'd buy a well experienced welder then even attempt a chemical bond such as JB Weld.

 

[mercuk]

Re: Steam? Exhaust? Normal?

I think you have just found your "steam" problem......

From what I can work out with the pics, the crack in the baffle plate would be letting water in to the cylinders hence your "steam effect"....Its pretty obvious becasue you can see the black soot deposits where exhaust gas has leaked through into the water cover (they shouldn't be there..:redface
I personally wouldn't trust JB weld for such a job but, it "might".. hold up if your after a cheap fix...:facepalm:

If it were me I would have two options: A) find someone how is handy with a TIG welder to patch up the cracks nice and neat or B) Replace the #19 baffle plate with a new one.
Option B clearly being the best one, but its up to you and how much money your willing to put back in to the engine, choice is yours........

What ever you option choose, good luck....

 

[mercuk]

Re: Steam? Exhaust? Normal?

Pics show fine for me.

These cracks will allow water to spray into the exhaust ports at some speeds, steam cleaning the piston, while at higher exhaust pressures can allow exhaust to blow into the cooling system, displacing cooling water and over-heating the motor.

You have found your problem, now repair it correctly.

JD Weld is NOT and approved repair, I would NOT risk an over-heat and possible engine distruction on a chemical fix. Nor would I recommend TIG welding, the material is too contaminated and extremely difficult to prepare an absolutely clean surfaces for welding.

Tho if the part is NLA, I would sooner see it TIG'd buy a well experienced welder then even attempt a chemical bond such as JB Weld.

You must of beat me to it by a few seconds.....

What the best thing about it all is that we pretty much say the same thing.....

 

[dOb]

Re: Steam? Exhaust? Normal?

OK, I'm starting to understand. I didn't realize that this could be the source of my overheating problem. I'll go ahead and replace it. Chris1956 had a link with a part number. It's not too expensive when you consider the alternative. I'l be off of the water for a couple of weeks, but I'll feel better about it. Especially if it fixes the problem. Thanks for all of the help. I'll post again when I get it all back together.

 

[dOb]

Re: Steam? Exhaust? Normal?

So far so good. I received the new baffle on Friday. It was smooth and shiny and had more reinforcements than the old one. I replaced all gaskets on the exhaust and cylinder cover and replaced the baffle. Last night I had a little time to try it out so I took the kids to the lake. No More Steam! The discharge stream is definitely stronger. After riding a while at high RPMs, it did get warm, but I could hold my hand under it with no problem. Warm, not hot.
Thanks again for all of the help and advice.