Slightly Steamy exhaust

Capt.Will

Capt.Will

Active Member
Aug 15, 2016
148
Lake St. Clair
Boat Info
1997 Sea Ray 330 Sundancer
Engines
7.4 MPI Mercruiser Inboards
Engine: 1997 7.4L Mercury Bluewater MPI - Closed Cooled

Issue: Port engine just seems to have a bit more steam exiting exhaust than the Starboard engine (on plane and at idle speed). It doesn't really overheat according to the temp gauge, however compared to the Starboard engine it does reach 170 degrees much faster upon a cold start.

When I come down off plane the Port engine does reach about 175-178 degrees for a few minutes then gradually backs down to 170 degrees.

Recent actions: Changed the Seawater pump housing/impeller with new kit. Made sure no debris was in the hose from pump to the Transmission cooler. Sea Strainer is clear as well.

Question: Could there be blockage in the Heat Exchanger or possibly a pocket within the exhaust manifolds? What are some possible reasons for this according to these symptoms? Are there any commons issues that happen with Heat Exchangers?
 
Steam is normal. Steam can appear depending on temp/dewpoint spread.

Your exhaust is coming out at 400+ degrees from the exhaust valve, that hot air hits water, so the result can be steam, and becomes more pronounced depending on water and atmosphere conditions.
 
CaptRonn said:
Steam is normal. Steam can appear depending on temp/dewpoint spread.

Your exhaust is coming out at 400+ degrees from the exhaust valve, that hot air hits water, so the result can be steam, and becomes more pronounced depending on water and atmosphere conditions.
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Thanks CaptRonn. I appreciate it. Only because it's much more than the other engine is the concern. And of course my concern is the quick to temperature on the Port engine is concerning as well. Any thoughts on that?
 
While it can be normal, it would not hurt to check the temperature of the manifolds and risers for both engines. I had an increase in steam and my gauges were normal, but the manifolds/risers increased temp from around 100 degrees in both engines, to the port one rising to 140 at 2K RPMs. This would not show in your gauges. After a lot of looking around, replacing impellers and heat exchangers, the intake hose was collapsing inside under high pressure, restricting some flow, causing the rise in temps and more steam in one side. This doesn't happen often, but checking things with a temp gun will ensure that everything is good.
 
superwa said:
While it can be normal, it would not hurt to check the temperature of the manifolds and risers for both engines. I had an increase in steam and my gauges were normal, but the manifolds/risers increased temp from around 100 degrees in both engines, to the port one rising to 140 at 2K RPMs. This would not show in your gauges. After a lot of looking around, replacing impellers and heat exchangers, the intake hose was collapsing inside under high pressure, restricting some flow, causing the rise in temps and more steam in one side. This doesn't happen often, but checking things with a temp gun will ensure that everything is good.
Click to expand...

Thanks superwa for that information.
Question: what particular intake hose specifically?
 
I have 2000 7.4 MPI engines (Inboards). My port steams way more than the starboard. I am no stranger to inboards and know that some steaming is normal but it steams a lot!. My port manifolds and elbows looked like hell (new to me boat). So even though I was not overheating, I put new manifolds, risers , and elbows on the port engine last weekend. No change in steam....darn! My quest continues........
 
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These steam threads are interesting. Steam is completely normal and yet all kinds of testing and speculation continues when someone sees steam. What part of normal do people not get? I recently retired from training medical students. Some of the early lessons involved teaching new students to look for common conditions that were the likely causes of observed medical conditions. The teaching theme was "When you hear the pounding hoofs from a heard of horses, do not look for zebras".
 
You could be missing the point. Not all engines steam, so if you have one that doesn't and then it starts to steam what does common sense tell you?
 
It was the hose from the strainer to the engine, so they experience high pressure suction and if the inside metal layer collapses it restricts the flow of water, just enough to make a difference.

Capt.Will said:
Thanks superwa for that information.
Question: what particular intake hose specifically?
Click to expand...
 
superwa said:
It was the hose from the strainer to the engine, so they experience high pressure suction and if the inside metal layer collapses it restricts the flow of water, just enough to make a difference.
Click to expand...
Thanks so much. I will inspect that hose and see what I find.
 
Unfortunately it may seem fine, as only the inner layers would collapse under high pressure suction. My recommendation. If you are going to remove to inspect, just throw in new ones and don't worry about them for years.

Capt.Will said:
Thanks so much. I will inspect that hose and see what I find.
Click to expand...
 
superwa said:
Unfortunately it may seem fine, as only the inner layers would collapse under high pressure suction. My recommendation. If you are going to remove to inspect, just throw in new ones and don't worry about them for years.
Click to expand...

I did remove the 1 1/4" hoses from the scupper to the sea strainer and sea strainer to the oil cooler. The hose did not seem in really bad shape but it was cracked on the exterior and obviously original so I replaced it. I also ordered the OEM hose that connects the oil cooler to the sea water pump. It is a really soft hose and I have folded it many times to replace the sea water pump. It may be soft enough to compress when under pressure. Should have it complete by the weekend to give it a try. Will report back after the weekend.
 
sbw1 said:
These steam threads are interesting. Steam is completely normal and yet all kinds of testing and speculation continues when someone sees steam. What part of normal do people not get? I recently retired from training medical students. Some of the early lessons involved teaching new students to look for common conditions that were the likely causes of observed medical conditions. The teaching theme was "When you hear the pounding hoofs from a heard of horses, do not look for zebras".
Click to expand...

I know it is normal. Every boat I have owned produces steam. But in this case when you go from normal to more than normal and I also have temperatures that are increasing coming off plane I am not worried too much but have some concerns. I appreciate your input though.
 
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