1990 350 EC - Merc 454 Inboards- Steam in exhaust / raw water flow

[rmarkko]

Hey guys, I relatively green as far as maintenance on my boat goes, but not totally ignorant to basic mechanics. Here's what I'm seeing... Coming in this weekend I was pushing a lot of steam of both exhausts. I immediately checked the strainers and no blockage/excess debris (tho port did have some rust coloring in the water).

It seems as though I am not getting enough water through to properly cool. Too little water is exiting at the exhaust, which could explain the steam, as what water did make it in could be evaporating from excess heat.

What should be my next step in troubleshoot, and/or what else might I be looking at here? Thanks for the help!

 

[kbsunlovers]

A thorough inspection of you cooling system components first, then:

Do you know the age of the manifolds and elbows? I think I'd lean towards an inspection there first. I'm not sure off the top of my head when the changeover to dryjoint happened, but if they're the old style and in salt, I'd be a bit suspicious.

 

[northern]

What I have found
A slight leak of raw water or anti freeze at the joint between the riser and the manifold will make steam when you start and last 2 minutes
A large leak of anti freeze at the riser you can smell it
At high RPM. 3800 for me you get constant steam even if there is no leaks between the risers and manifolds
On cold days you will get steam when starting even if there is no leaks at the manifolds and riser joint.
Do you have to top up the anti freeze? If yes you have a leak. It is probably at the riser to amifold joint.

 

[HGM]

What temperature are the engines running? Are they maintaining or fluctuating?

 

[Mike Blake]

OK all that just said is good,but when have you changed the raw water pumps???? That happened to me and all it was,were the pumps!!! Cheap. I changed both and have a spare. I would look at that first.

 

[Jimmy Buoy]

What I have found
A slight leak of raw water or anti freeze at the joint between the riser and the manifold will make steam when you start and last 2 minutes
A large leak of anti freeze at the riser you can smell it
At high RPM. 3800 for me you get constant steam even if there is no leaks between the risers and manifolds
On cold days you will get steam when starting even if there is no leaks at the manifolds and riser joint.
Do you have to top up the anti freeze? If yes you have a leak. It is probably at the riser to amifold joint.

The O.P. said that his engines were raw water cooled, so he won't have any antifreeze to check...