Acceptable amount of steam from exhaust

[Briank117]

Hey gang,

While under power (3000rpm), I have steam blowing out both exhaust ports. If I pull back to idle (650+/-), it disappears in about 5-6 seconds. I can cruise all day at 6-10 knot and not see any steam until I throttle up. Temp & oil gauges read fine—and stay consistent. High flow of water out both exhausts—New impellers installed back in spring.

Is there an acceptable amount of steam displacement, or should the boat not steam at all?

(318s raw water cooled. I know the manifolds and risers are dated. Otherwise, motors run great.)

[prowlersfish]

A small amount is not abnormal . Excessive steam is normally due to poor water flow ( even if it looks fine) Risers many times can be at fault . Steam will increase as the temperature drops and the dew point changes .

[Boppy]

I get more steaming on colder days at higher rpms (~3000) from my single 318 rwc engine. Risers are ok, oil, temp, etc all good in spec. Our lake water doesn’t usually warm up until July. I’m usually just putt-puttering around at <2000 rpm and it don’t see much, if any, steaming from exhaust.

[The Dog House]

When I bought my 1971 Trojan F26 it had steam coming out of the exhaust. The person I bought it from said it was normal. I changed the impellers any way and it still steamed with the new impellers. I figured it was normal. I ran the boat with steam coming out of the exhaust like that for 7 years.

At the 7 year mark I took in a lot of debris that clogged up the strainer. I shut the engine down when I saw the temperature increasing but the lack of water ruined the water pump. I installed a brand new water pump and had no steam whatsoever coming out of the exhaust. The boat also ran better than it ever had in the prior 7 years. After 45 years of use the old water pump wasn't working fully, even with new impellers and cams. I didn't realize that until I put the new water pump on.

New water pumps are about $700, so its not a negligible cost. My boat ran much better, though, once I put the new one on.

[Briank117]

Appreciate the insight!

I plan to remove/inspect the cooling system over the winter.

I figured the (now) cooler/cold water may have had something to do with it as well.

As always, thanks for the help!

[Briank117]

Hey gang,

Just an update if this could help anyone in the future. F32 with 318s.

Per usual, I replaced Impeller/thermostat early spring. Decided to replace both sets of risers/manifolds as well. Took a few slow cruises, all temps were fine. No steam. All good, right?

This past weekend, took her out and ran 3k rpm for half hour. Still had a ton of steam from port motor. Minimal from starboard. Last night I decided to pull apart the Oil cooler. Glad I did! 2 sea strainers are now on order. Back flushed both oil coolers. Surprised at how much more water is dumping from the exhaust.

Woohoo!

[kallen]

On my 81 F-32 (318 raw water cooled) I had a steaming issue when on plane for 5 years. Did everything I could, One day I noticed that the water pump pulley was a little closer to the pump housing itself. The front seal of the pump was sucking air. Replaced the pump and the problem was cured. Still have a brand new in the box G-7 pump for sale. Sold the boat.