Too much exhaust?

[Peter Lewis]

We have a 1993 Mk 1.5, with a Universal M35B engine and 1750 hours.

Over the last three seasons, we have seen a notable increase in engine exhaust when motoring at cruising speed (2000-2500 rpms).  The exhaust color looks like greyish white to whitish grey; definitely not black or blue. It normally dissipates not more than 5 - 10ft behind the transom.  There is no unusual soot buildup on the transom, nor are we burning oil.  The exhaust doesn't smell like antifreeze.  The engine runs smoothly.

Cruising at 2000-2200 rpm keeps the engine temp at 160-170, and if I open the throttle to 2500, the temp climbs to 180.  There is a clear increase in white/grey exhaust with higher engine temperatures.  Once the engine is hot, If I throttle back, shift to neutral, and raise the revs to 2500 again, there is just as much exhaust with no load.

I interpret the pattern as indicating insufficient mixing of exhaust gases and raw water.  However, the raw water system checks out fine-  no obstructions at the intake, new impeller, recently cleaned out the 3" heat exchanger completely, mixing elbow seems fine, and there is water coming out of the exhaust.

Is it possible that I have insufficient raw water flow?  Possibly due to a worn pump?  I recall reading about the wear to the facing plate causing the pump to work less effectively.  I'm still running with a 20 yr old Sherwood pump, so it might be a good time to replace it anyway.  Does anybody know what the flow rate should be for the Sherwood pump?

Alternatively, is there anything inside the water lift muffler that could be the culprit?

[Ron Hill]

Peter : The muffler is a simple box with one inlet pipe going almost to the bottom and the exhaust pipe about an inch from the top.  Should not be a problem!!

I'll guess that your Sherwood is worn after 20 years.  How do you plan on measuring the flow anyway?

I'd try a new face plate if you have a 903 model pump along with a new impeller if it's also aged.

A few thoughts 

[Jim Hardesty]

If your Sherwood pump is like mine you can just flip the face plate.  My original face plate was bronze, the new one is steel.  According to the supplier thats what they make now.
Jim

[Peter Lewis]

Thanks for the feedback guys.  I was planning on measuring the flow by disconnecting the waterline at the exhaust mixing elbow and collecting water for a half minute or so with the engine running.  I'll go ahead and order a new pump anyway, as I'm starting to see signs of water leaking through the weep holes. 

[TonyP]

Ours (25mpx) is doing the same. I was thinking a fouled inlet. We are lifting tomorrow to antifoul so will see. We have recently had the HX redone as well as new impeller. I am sure it is steam more than smoke. Like Peter's, it sits on 165/170 at 2000rpm but rises to 190/200 or so at 2600rpm which is max at the moment under load with our 2 blade 15x9. It will reach 3100 in neutral.
cheers
Tony

[Ken Juul]

I found this info on a site that is selling engine snake oil...take it for what you think it is worth. 

WHITE sometimes more GREYISH smoke ..

To go directly to products that reduce engine WHITE smoke click here

White smoke is caused by raw, unburnt fuel passing into the exhaust stream. Common causes include ..

    Incorrect fuel injection timing
    Defective fuel injectors
    Low cylinder compression

Low cylinder compression may be caused by leaking valves, sticking piston rings, ring wear, cylinder wear, or cylinder glaze.

When white smoke occurs at cold start and then disappears as the engine warms up, the most common causes are fouling deposits around piston rings and/or cylinder glazing.

Continuous evidence of white smoke indicates a mechanical defect, or incorrect fuel timing.

Water entering combustion spaces will also create white smoke.  Faulty head gaskets and cracked cylinder heads or blocks are a common cause of water entry .. unfortunately, expensive mechanical repair is the only proper solution here.

Google also mentioned it might be steam in the exhaust, which seems to be your train of thought.  You might try holding a rag in the smoke clear of the cooling water stream, if after a few minutes in comes back damp, then steam.  If it smells of fuel, then maybe injectors.  The last paragraph above mentions water entering the combustion, old fuel may also be a cause.  Try running the engine out of a jerry can of new fuel and see if it makes any difference.

[Peter Lewis]

Here's an update:  I had a new Oberdorfer water pump delivered from Catalina Direct.  In my dockside tests, the old Sherwood delivered about 1 1/8th GPM at idle, vs. 1 3/8 gpm for the Oberdorfer.  The difference at cruising RPM (2200-2500) was even more pronounced, but I didn't take measurements with the Sherwood before removing it.  The "field test" consisted of three days of motoring into either calm seas or headwinds from our home port to Desolation Sound..... pleased to report that the exhaust has almost completely disappeared, and the engine operates at a lower temp for any give RPMs.  Problem solved!

[Ron Hill]

Peter : Glad that you got your problem solved!!

I'm surprised that such a small difference in the flow of raw water cleared up that problem, because usually white smoke is caused by unburned fuel? 

My thought

[TonyP]

Great news Peter
Since hauling and repainting the underside (and noticing no growth at the intake, though pretty dirty on some sections of the underside and prop) the engine did perform slightly better. I had the mechanic come aboard for a test run and he feels the engine is getting tired.
Maybe a new Beta might be in order though at A$8750.00 plus installation it wont be any time soon.

cheers

Tony