Exhaust Problems ??

[ermelind]

I have noticed what I consider to be an excessive amount of steam or (?) from the exhaust lately. I have plenty of water coming out - the engine is not overheating (temp ~180degrees). I did notice some exhaust odor in the engine compartment last time I ran the engine - I wondered if the "steam" condition might be caused by an exhaust leak in the elbow region??

[Don Moyer]

Ermelind,

It's difficult to be certain, but I consider the cause and effect relationship of the two abnormalities you're reporting to be in the direction of the steam causing a slight odor to manifest through a pre-existing exhaust leak, rather than that the exhaust leak has somehow caused the steam. This, of course, leaves unanswered the question of what is causing the steam.

I do believe that you're focusing on the correct spot in your exhaust, which is the immediate area of the cooling water inlet fitting. My best guess is that there is a build-up of scale and mineral deposit in that location, where engine cooling water has been splashing into the water entry fitting of the exhaust, and some of the water is now splashing "upstream" and turning to steam as it comes in contact with the hot part of the exhaust.

I would remove and examine the entire hot section of the exhaust, between the back of the manifold and the water lift muffler, including the water entry fitting. I believe you'll find both the source of the steam and the small exhaust leak.

Regrettably, this is some of the worst boat work that I can imagine, but if there is a build-up of crud in this area, the removing of the restriction will not only cure your steam, but you will undoubtedly experience much improved engine performance.

Best regards,

Don Moyer

[ermelind]

Thank you - I will give your suggestion a try...

[ermelind]

wrapped hot exhaust section

Is it possible that the excessive amount of steam I have been experiencing in the exhaust could be caused by having the hot potion of the exhaust wrapped in fiberglas tape?? I had the boat surveyed last year (insurance) and one of the items the surveyor said needed to be taken care of was that the hot section of the exhaust should be covered (from the flange attached to the manifold to the hose entering the muffler). My guess would be this would increase the heat in this section, and cold water entering it would be more likely to turn to steam. Also would seem to me this might be a bad thing for the elbow and flange, as they might sweat and therefore rust more quickly. I don't remember having this problem prior to having the hot portion wrapped. I pulled the elbow and flange off the manifold (broke one of the bolts in the process, unfortunately) - and have noticed a yellow liquid weeping from pores in the metal now that it is in the air....

[Don Moyer]

It is first necessary to clarify the difference between steam and white smoke. White smoke will linger behind the boat for several boat lengths, while steam will dissipate quickly - normally within 5 to 10 feet. White smoke is almost always caused by oil entering the combustion chambers and burning along with the fuel mixture. Steam will normally be caused by one of the following conditions:

1) In the cool part of the season, it's rather common within our northern operation locations for people to report a "vapor" coming out with the exhaust on their boats. This vapor is simply a matter of warm moist air cooling and condensing behind the boat. The problem goes away as soon as the weather warms up a bit.

2) Early model cooling systems will create a small amount of steam until the engine gets fully warmed up. While an early model engine is still cool, most of the cooling water is being recirculated, leaving an insufficient amount of engine cooling water to be discharged into the exhaust system to cool the hot section, and what water does enter the exhaust system turns to steam. As soon as the engine warms up, more water will be discharged to cool the exhaust system, and the steam should dissipate.

3) In both early and late model engines, cooling water flow may have reduced due to a defective water pump or a restriction in one of the cooling hoses, so that there is no longer sufficient water flowing through the engine to keep the hot section of the exhaust system cool, and a small amount of steam may be developing in the part of the hot section where the engine cooling water enters the system.

4) Steam will sometimes be created as the hot section slowly clogs with precipitate where the engine cooling water enters the hot section, usually just above the inlet to the water lift muffler.

NOTE: In both (2) and (3) above, the creation of steam may be somewhat exacerbated if the hot section was recently wrapped with an insulating material, since the insulating material will result in a hotter temperature
within the hot section.

5) The most serious scenario would be steam caused by a small amount of water leaking into the exhaust manifold through a crack in the block, head or manifold. Steam created by a small crack in one of these cooling water jackets will usually elevate exhaust back pressure within the manifold or the rest of the exhaust system, which will - in turn - cause a very thick caramelized brown goo to form on the stems of intake valves. We have several cases on record where intake valves have stuck open in only 5 to 10 hours of operation.


Best regards,

Don Moyer

[ermelind]

Thanks for the reply - I believe the problem is steam as opposed to smoke - it seems excessive, but it doesn't seem to linger for several boat lengths. The problem also only happens under load - I notice no steam when at idle or when the prop is not engaged...

I've removed the exhaust flange from the manifold, as I mentioned - and in the process, broke off the bottom bolt - I am therefore now considering removal of the manifold. (In the process of removing the flange, I have noticed some extensive rust in that area of the manifold - I also either need to get that bolt out, or replace the manifold with a new one.) What do I need to be careful of when removing the manifold?? I have loosened the nuts on the mounting studs (seemed to loosen easily) - but that is as far as I have gone...
Thanks.

[Don Moyer]

The most important caution regarding removing a manifold, especially in cases where there is a lot of rust present, is to not pry too hard from either end of the manifold if one of the end studs is not releasing. It's possible to create enough leverage throughout the length of the manifold to pull a stuck stud out of the block, and with it, a good piece of the block as well.

Best regards,

Don Moyer