Steam in exhaust typical on gas 396?

[thatchh]

Hello All,
I am in the process of purchasing a 2004 Carver 396 with Crusader 8.1 MPI engines (395hp?) that have 190 hours on them. In a preliminary sea trial,they seemed to run well, but put out quite a plume of steam on both sides at planing speed (18-20Knots, 3500rpm). Is this common on these big boys, or does this indicate poor water flow? I don't want to get stuck with a big engine repair.
Thanks,
thatchh

[Viper]

Welcome aboard.

This is common with any engine given the right circumstances. It's usually due to poor raw water volume from a failing impeller or restriction anywhere from the cooler, heat exchanger, exhaust manifold, etc. All these are the most common culprits. Exhaust manifolds of that age in a salt water application are on borrowed time so even if it turns out to be one of the other items, you'd want to consider replacing the manifolds.

Keeps us posted.

[thatchh]

Thanks for the advice. I'm pretty sure the manifolds are fresh water cooled. I'm hoping at worst, it's just the elbows. I suspect impellers, and possible impeller bits in the heat exchanger which could allow the manifolds to overheat. According to the broker, the boat spent its life in fresh water. I will monitor the whole cooling system with an infrared thermometer during the survey sea trial.

[bud37]

Qr Bbpost Thanks for the advice. I'm pretty sure the manifolds are fresh water cooled. I'm hoping at worst, it's just the elbows. I suspect impellers, and possible impeller bits in the heat exchanger which could allow the manifolds to overheat. According to the broker, the boat spent its life in fresh water. I will monitor the whole cooling system with an infrared thermometer during the survey sea trial.

If your offer is contingent on favourable survey/sea trial, then the clearing up of this issue ( exhaust steam) should hopefully be on the seller as part of the deal. Amazingly low hours, good luck with your survey, hope it works out well for you.

[km1125]

The other thing to consider is the temp and humidity when the boat was run. Cooler temp with high relative humidity make the exhaust condense very quickly upon leaving the boat.

Definitely makes sense to check water flow and exhaust temps and plan to replace impellers anyway (because then you KNOW FOR CERTAIN when they were changed!).

[Viper]

Qr Bbpost.......I'm pretty sure the manifolds are fresh water cooled. I'm hoping at worst, it's just the elbows.......

I should have been a little clearer in my reply. Whether the manifolds are fresh water cooled or not isn't as much a concern for this particular symptom as the condition of the elbows. A restriction in the raw water outlet passages at the end of the elbows will cause a spray of water rather than a column. The spray is easily vapourized by the hot exhaust resulting in steam.

For the benefit of those in salt water applications that are running raw water cooled manifolds of that age, even if they don't show any outward signs of degradation such as steam, rust, etc. one should consider replacing them before they cause a major engine failure from ingesting water.

[Viper]

Qr Bbpost The other thing to consider is the temp and humidity when the boat was run. Cooler temp with high relative humidity make the exhaust condense very quickly upon leaving the boat.

Definitely makes sense to check water flow and exhaust temps and plan to replace impellers anyway (because then you KNOW FOR CERTAIN when they were changed!).

I agree on both counts KM. Ambient conditions definitely play a role on what you see coming out of the exhaust.

In any new acquisition, one should address the regular maintenance items whether there are problematic symptoms or not. Unless the seller can show that specific items were looked after recently, it's recommended that that items such as all fluids be changed, filters, replace all impellers, check quality of coolant, perform ignition tune-ups, etc. On an EFI application, it's advisable to hire a tech to hook up diagnostic software/tool and look for red flags that may not be obvious externally. As KM said, you're then assured these items were addressed on a certain date and now have a benchmark from which you can then plan this maintenance again.

[DanM]

I also have a 2004 396 only mine has VP 8.1's. They are known to steam more than Merc's in the same set up but I can't say if Crusaders do the same. I've had the boat for 8 years and am meticulous about engine up keep. Every thing checks out at idle as well as underway and are identical on both engines. I had a mechanic look at it to back me up. He stated that it's normal for my set up with VP's. I know it's not specific to your boat but at least it's good anecdotal information. PM me if you have any specific questions about the boat. I'd be happy to share what I can.

Dan

[Samuel]

IMG_0529.JPG

2001 356 carver 8.1 volvo 375 hp. I had it for 7 years change manifold and riser twice. Change thermostat, impellers, all antifreeze hose's did not change a thing. Boat runs like a champ cruises at 3600 rpm doing 27 mph burns 27 gallons per hour all water temperature normal.

[jcoll]

Qr Bbpost

IMG_0529.JPG

2001 356 carver 8.1 volvo 375 hp. I had it for 7 years change manifold and riser twice. Change thermostat, impellers, all antifreeze hose's did not change a thing. Boat runs like a champ cruises at 3600 rpm doing 27 mph burns 27 gallons per hour all water temperature normal.

Wow!! If that were my boat I'd say I have a problem but apparently you don't. It appears you've done a lot of cooling system maintenance. Do you know what elbow outlet temp is under cruise?