Rubber Impeller In Anti-Freeze (Not Seawater) Side of Circuit - Replacement Interval

[rardiH36]

My engine was originally a raw water cooled engine only for seawater running directly through the engine block.

It was adapted to an external heat exchanger system with addition of a second external pulley powered pump for the seawater circuit. The engine's block-integral pump was given the task to instead circulate the anti-freeze side of the circuit. This pump employs a rubber impeller.

Question: I've read that its a good idea to inspect/change the seawater rubber impeller at least once per year. But how about a rubber impeller in the anti-freeze circuit? It would seem to me that the anti-freeze also provides a lubricating function ... thereby increasing the life of the impeller? But I don't know. The maintenance schedules that I have seen seem to refer only to the raw seawater side, since many (most?) diesels have no maintanence "hard impeller" pumps for the anti-freeze circuits (like a car).

regards,
rardi

 

[Stu Jackson]

Freshwater cooled diesel engines with a separate

raw water exhaust/cooling system do have recirculating pumps for the freshwater. Most are not rubber vane impeller pumps. This is our freshwater pump on M25 engines: http://www.marinedieseldirect.com/c...arts=&printservice=&printoperators=&comment1=

As long as the material of the rubber is compatible with the anti freeze, the replacement intervals should be the same, simply 'cuz the issue is not the wear of the particular fluid, but rather the wear of the rubber impeller itself.

 

[Maine Sail]

raw water exhaust/cooling system do have recirculating pumps for the freshwater. Most are not rubber vane impeller pumps. This is our freshwater pump on M25 engines: http://www.marinedieseldirect.com/c...arts=&printservice=&printoperators=&comment1=

As long as the material of the rubber is compatible with the anti freeze, the replacement intervals should be the same, simply 'cuz the issue is not the wear of the particular fluid, but rather the wear of the rubber impeller itself.

Stu,

Most on engine fresh water circulating pumps use a metallic centrifugal type impeller or vane or a hard plastic one. These pumps do not generally prime but rather basically only circulate. This is the reason, when you have air in the system, why they can become air bound. I have yet to see one with an impeller like we use on a raw water circuit but that is quite possible in a raw water conversion.

In this case the impeller should probably be replaced on an annual basis seeing as the rubber vane impellers don't much like antifreeze. At a minimum check it yearly.. If there is a possibility of locating the original centrifugal pump for that engine, and converting back, it might be a good idea..

 

[sailaway78]

Yearly

Impellers are cheap, and easy to replace. For the risk involved, change every year, regardless. If the one you take out looks good, keep it for a spare. Since I just had one fail for the first time ever, that had less then 30 hours on it, I think I will now keep two spares on board. At least one new one, plus a used take out, just for in case. When you have one fail, and you aren't sure why, makes you a little nervous when you have a long way to go, and no longer have a spare.

 

[Stu Jackson]

Freshwater side -- "Burping" the Engine

Most on engine fresh water circulating pumps use a metallic centrifugal type impeller or vane or a hard plastic one. These pumps do not generally prime but rather basically only circulate. This is the reason, when you have air in the system, why they can become air bound.

You're right. The link to the pump shows just that. I call it "BURPING" the freshwater side, which is why I wrote this, see Reply #6: http://c34.org/bbs/index.php/topic,4518.0.html

This is for an M25 series Universal (D850, D950 Kubota tractor engine).

Thanks,

Stu

 

[kloudie1]

Another reason for changing often is that this circulating impeller will run at engine temperature (160?) instead of seawater temperature (80). If it has a radiator cap on the closed antifreeze side, the lip seal will have a tough time with the higher pressure too..

 

[rardiH36]

Thanks all.

Regarding Kloudie's observation that high engine coolant temp might be detrimental to the rubber impeller: One quirk on my engine is that since it was designed for seawater cooling, the thermostat housing on the engine only accepts Yanmar's 140F thermostat, notwithstanding anti-freeze now flows through its veins. (My understanding this because much above 140F, seawater will start to deposit insoluble salt and other minerals within the engine's channels. Hence the low temp limit.) The antifreeze coolant only becomes very warm, never scalding.