Engine Exhaust Back Pressures

[ALLAN WARD]

I own a PERKINS PRIMA M50 and the manufacturer stipulates that the exhaust back pressures should not exceed 10kpa . Using a reasonably good quality guage l discovered that my engine's back pressure ranges between 15 and 20kpa . My question is , what damage would the engine suffer at these higher exhaust back pressures ?

[manitu]

Exhaust pressure will cause loss of power, increased fuel consumption and possible high exhaust temps.

Where do you take the reading?
I'm not too familiar with marine diesels, so I wonder if the amount of cooling water injected to the exhaust have a big impact on this.
Normally exhaust pressure is a result of exhaust design only.

.manitu

[ALLAN WARD]

Many thanks Manitu for your reply . I measured the pressures from my waterlock which is positioned +/- 500mm from the exhaust injection elbow . From what you are saying is that engine performance is being affected but there is no damage taking place with the higher backpressure . I was surprised to see how low the M50's back pressure spec is as l think the 4108 Perkins is 20kpa .

[S/V Alchemy]

I would suggest you need to consult a reputable marine diesel mechanic and to confirm that your pressure gauge is properly calibrated. I am not convinced that you aren't reading "pressure" at the wrong location. Naturally, the water is being accelerated by the pump, so the question is: does "exhaust" include water?

[manitu]

High exhaust temps can cause damage to the exhaust valves, but your readings does not sound to bad. Back pressure is the extra force needed to push the exhaust out of the engine. I would test again, before the water injection point if possible.

.manitu

[ALLAN WARD]

The exhaust temperature meaning the heat of the pipe connected to the exhaust elbow is surprisingly cool and l have always been suspicious of my engine temp guage as it sits around 50 degrees c . I would have expected an engine temp around 80 degrees c .

[BergeronWarren]

Hello. In 2 days, I plan to have a mechanic look at this but I would love to hear your thoughts. After smelling exhaust and then seeing a steady drip (/2sec), I pulled the 2.5" hose that goes 2' from engine to Vetus muffler. The connection at the mixing elbow was at a difficult angle and I was hoping my reinstall with more bendable hose would improve the seal. However, when I pull it I find that previous owners used a 3" section of 2" hose at the Vetus connection to accommodate the smaller fixture. Not only is this dangerous for fumes, it is a reduction.

What gauge hose your Prima engines use?

Also, I considering asking the mechanic to replace the elbow and manifold which look corroded. This may be another opportunity to use a 2" fixture, but it returns to the question of back pressure. Our boat is 32,000 lbs. so we do not wish to reduce our 49 hp anymore.

What are your thoughts?

/Matt Warren, s/v Tashtego (1983 Lord Nelson)
216.401.6813