Mercruiser 350, excessive exhaust steam

[Topaz28]

Have twin inboards, starboard motor has excessive exhaust steam both at idle and while running. Closed cooling system, temperature appears to be normal, checked the obvious for raw water blockage, replaced thermastat, heat exchanger was just cleaned and serviced. Wondering if impeller or oilcooler needs to be replaced...

 

[HT32BSX115]

Re: Mercruiser 350, excessive exhaust steam

Have twin inboards, starboard motor has excessive exhaust steam both at idle and while running. Closed cooling system, temperature appears to be normal, checked the obvious for raw water blockage, replaced thermastat, heat exchanger was just cleaned and serviced. Wondering if impeller or oilcooler needs to be replaced...

It's very possible that you have enough raw water flow to keep from over heating the engine but not enough flow to keep the riser/elbows cool. If you have not looked at the raw water pump impeller it may have partially failed leaving only a few vanes remaining etc.....

You also may have raw water pump remnants (from this or a previous impeller failure) partially plugging the oil cooler and/or power steering cooler(s) If you have not already done it you need to remove your raw water line to the oil/PS heat exchangers and ensure that they are clear.


Regards,


Rick

 

[Topaz28]

Re: Mercruiser 350, excessive exhaust steam

Thanks very much!

 

[newport dave]

Re: Mercruiser 350, excessive exhaust steam

It would be a good idea to remove the exhaust elbows and check for raw water in the exhaust passage of the manifold. This will cause steam in the exhaust and can cause serious engine damage in a very short peroid of time.

 

[Dshow]

Re: Mercruiser 350, excessive exhaust steam

I have a 2001 5.7L Mercruiser with the same issue... Out of the driver side thru-hull exhaust, you can sometimes see steam. I have checked my thermostat housing and the hose going to the driver side riser is much hotter. I was going to pull my thermostat housing and see if there is any reason why it would divert less cooling water to the driver side...

This has not caused me any issues to date... knock on wood...

 

[HT32BSX115]

Re: Mercruiser 350, excessive exhaust steam

If you have enough cooling water flowing thru your riser/elbows, you should be able to put your hand on top of them........they'll be warm but not hot enough to burn you. If you don't have enough flow they'll get pretty hot. "too hot to handle"