Deteriorated Sherwood Pump Impeller!

[Bob4203]

I was experiencing some overheating when running my Universal M-18 with a noticeable lack of sufficient exhaust flow recently. I did not allow the engine to overheat (280 degrees too long).

When removing the cover off my Sherwood Water pump I noticed that the impeller was severely deteriorated (crumbled bits of rubber and 1/3 of the rubber flanges gone).

The engine is logging 500 hours and I do not believe the impeller was ever changed by the prior owner. Now that Lake Lanier is still low, I seldom venture from the dock these days, so I figured age and dry rot has taken its toll. I did remove the hose from the pump to the heat exchanger and removed the "T" fitting on the pump that caught a few of the rubber chunks. Where else can the rubber get lodged? Fresh water is pumped through the impeller directly to the heat exchanger and out through the exhaust port.

Here is my question:

I am concerned that I might have some rubber in the heat exchanger tubes that would restrict flow. Having never taken off the heat changer can someone provide some good tips for inspection and cleaning? Obviously I release the coolant when removing the heat exchanger. Would I have to use compressed air? Would be it wise to replace the exchanger with a larger unit at this time? The boat has always operated in fresh water.

Any pointers would be appreciated.

Thanks
Bob
Catalina 30
Universal M-18

 

[Ozzie]

Impeller Vanes: Lost in transit

Concerning missing impeller vanes (blades) I suggest the following:

1. Remove as much rubber debris as you can from the impeller housing and inlet/outlet fittings and hoses.
2. Replace the impeller with new ones being careful to have all folded vanes oriented in the rotation direction for your pump.
3. Install the cover on the fuel pump and, if your pump model requires in, install a new gasket at that time.
4. Re-connect all hoses and check for water leaks.
5. Run the engine long enough to reach operational temperature - under load, not just at idle - and monitor water temperature for at least 10 to 20 minutes to see if the temperature raises.

If the water temperature remains stable at or, below recommended levels by Universal, then: you are done and there is probably no rubber pieces fouling your system

If the temperature rises above the recommended level (overheating) then: you have rubber bits clogging up some part of the system, probably in the heat exchanger. You have two choices:

A. Attempt to clean the heat exchanger yourself either while still attached to you engine or, after you take it off. I is not really that difficult to do; go to the Universal Diesel site http://www.marinedieseldirect.com/universal/shopping/ and get schematics of the heat exchange system for your Universal engine.
B. Have a competent Marine diesel mechanic take a look at the system and give you a quote on what it will cost to get the job done.

Feel free to correspond with me directly if you have any questions; I am not a mechanic, but I do most of the simple maintenance on my O'Day 34 including the engine systems. You can reach me at ozziepedrera@yahoo.com

Good luck.

Ozzie

 

[Bob]

Thanks Ozzie

Appreciate the response Ozzie.

After doing a search I see many have had the same issue and have followed the same steps as you describe. My heat exchanger as small as it is for my M-18 is very accessible and easy to remove. I have an air compressor at home and if as you say, the temps go back up, I will remove the exchanger and try to remove any debris via air pressure or rods. It would be nice to see a schematic of the exchanger interior to see just what I am dealing with.

My next concern; however, is the path from the exchanger. Some refer to a "mixing elbow". Can a small piece of debris, say no larger then a dime get stuck in any fitting after it leaves the exchanger? That can present a challenge as well.

I will also assume that when removing the exchanger I will also loose coolant and therefore will have to "bleed" the system once its all back together.

Thanks

Bob

 

[Glenn]

You should see improved exhaust flow

when the impeller is replaced. If you do not, then there is a problem elsewhere. Since your boat has always operated in fresh water, that would rule out build up at or in the raw water system. You should have a raw water strainer before the Sherwood, clean it as debris can clog it restricting water flow. Yes, debris can clog the mixing elbow, however, I think that you will most likely catch all but the smallest pieces of impeller in the heat exchanger. Since you are in fresh water, you can rule out the salt build up we see in salt water, always a source of potiental problems.

 

[Bob]

Strainer Clean

My intake strainer on my 1988 Catalina is simply.........very small and quite simple! It is comperable to the strainer used in-line for a water system such as the galley sink! It is a minature compared to the big brass unit I had for my big Perkins 4-108 engine years ago on a different vessel. Obviously Catalina engineered this little unit in and found it totally acceptable for the Universal M-18 engine. It is very accessible, screws apart and is easy to clean. The filter mesh is a whopping 2-3-inches in length.

With the lake stagnant, algae growth is as accelerated on the bottom as barnacles in the Bay of Fundy! I am constantly checking the mesh for debris. The intake is a simple thru hull with no exterior strainer.

I am hopeful that the new impeller and the replacment water hoses from the strainer to the pump housing and the one to the exchanger will make a difference.

I do feel compelled to take the exchanger off to clean it up and gain some valuable knowledge.

Thanks
Bob

 

[Stu Jackson]

Bob, you could blow out the hoses

with a dinghy foot pump, as we did recently. Other advice of removing and checking the HX is very good. Sherwood parts are available at DEPCO, look around in the C34 Association website and search on DEPCO and you'll get the info.

 

[Ron pence]

A second filter

And there are those who, just for this reason, suugest another filter AFTER the impeller.

 

[Ozzie]

The vanes are going to be samall

The way I have cleaned the tubes in the impeller was using a gasp! wire hanger! If you have an air compressor it will work well if you push the air against the normal flow of coolan. Otherwise, you might just jam up the rubber parts harder into the tubes. It is unlikely that the parts clogging the system are the size of a dime; I'd guess they are much smaller than that since the impeller rotation action would normally chew up the parts before they separate.

Good luck!

Ozzie