Electric water pump

[basslover911]

Originally Posted by Nerys

I was thinking LEAVE the oem pump in place and I figured a replacement pump would have an IN and an OUT which I could simple insert into a cut in half radiator hose. Done. No mounting hassles no running lines no removing the oem pump (that is an issue will water flow ok if the oem pump is left in place and not spinning? I have no idea on that one.

Remember I want to go alternator free as well so power consumption is pretty critical. a 1000watt motor "seems" to my gut check to be seriously over kill.

Well except if you leave the oem pump there then you also have to circulate water through it which gives resistance meaning even LESS efficiency ... just one thing to think about (well... unless you take out the propeller in the water pump but then again that would mean dismantling it and doing even more work).

I want to do this also and to go alternatorless... what do you think a good electric motor would run this pump then if not 1000 watts... 250 watts? (im using these figures because these motors are really cheap because many people use them for electric bicycles

[Nerys]

I really don't know. I was hoping it would be a heck of a lot less than 1000watts. I can run a 1000watt motor for very long on a pair of even really good batteries. Hoping for under 100 watts. How FAST does the collant need to flow? in fact HOW DOES the coolant flow. I know the flow rate through the radiator is VERY slow is there a bypass where it runs much faster? how many rpm is the water pump even spinning at?

[smokeyj]

Well the Davies Craig system

Which they claim is suitable for up to 3L car. Uses a pump that is 13V 7.5A about 100W
This pumps 20gpm (no head)

Throw in alternator loss and the mechanical power the electrical pump would absorb is maybe 300W call it 1/2 hp

These guy claim that the water pump is dimensioned for the worst case which they say is idle where there is low flow from the pump. Such a pump has way way too much flow at hiway rpm and so causes loss.

So kind of the same argument as the grill block.

[Nerys]

so a larger radiator and a 40-50watt motor might work for a metro?

[smokeyj]

How would I know? I am just telling you what they said!
But seems reasonable. In a related note there is a company called EVANs that makes a different coolant that can run hotter before it boils.

Coolants Engine Cooling Systems

So this would allow you to run the engine hotter without fear of boilover. I don't know what the next thermal limit is in the engine.

I vaguely remember that HONDA F1 cars were running straight water at 50 psi or so to get really high coolant temps that would allow for smaller less draggy radiators.

So I suppose the ultimate setup would be some kind of electric pump, small radiator and high temp coolant. To allow for smallest possible inlet.

[Nerys]

well I have plenty of space in the front. enough for more than 2 radiators. I can get cherokee radiators pretty cheap $50-$60 and they have at least 3-4 times the cooling capacity of the metro radiator.

the smaller the electric motor I can use the better :-) I guess I really just need to test but thats definitely a spring project. any figures from winter are useless since its so cold out.

[rgathright]

Originally Posted by Nerys

well I have plenty of space in the front. enough for more than 2 radiators. I can get cherokee radiators pretty cheap $50-$60 and they have at least 3-4 times the cooling capacity of the metro radiator.

the smaller the electric motor I can use the better :-) I guess I really just need to test but thats definitely a spring project. any figures from winter are useless since its so cold out.

I ran into a lot of problems with winter electric fan/ water pump installs in my project cars in the past as well. Good idea to wait.

[smokeyj]

Well I have been puzzling over this problem. I have come to the conclusion that indeed you don't need to pump huge volume of coolant. The problem is mostly about airflow.







I can't seem to find radiator efficiency data, but I was able to find some good data on oil coolers (really the same problem)

http://www.oilcoolers.com/LCHX%20Specifications.pdf

If you plow through this one thing you will see is that heat rejection is not strongly dependent on oil flow. For example if you look at the 8406R radiator you see that for an air flow of 20lbs/min the heat rejection varies from 200 BTU/min to 320 BTU/min
Over a 5 to one variation in the oil flow rate. So pump the oil as fast as you want , it doesn't make much difference. The air flow is what does the magic.


I suppose another way of thinking about it would be if we pump super fast so that the water is absolutely flying through the radiator then there would be almost no loss of temp of the water. You would have a situation where a lot of water lost a little bit of temp in order to shed the required heat. In this situation the entire radiator would be a one temp since the water is only dropping a tiny bit in temp. Since the radiator is at a higher average temp it can shed more heat.

The other situation is when you are pumping slowly so that the coolant loses a lot of temperature through the radiator. Somewhat less heat is shed, since the back end of the radiator is cooler it is somewhat less effective a dumping heat so in total less heat is removed.

So the question is in the automotive situation where are you with respect to this point of diminishing returns?

[Frank Lee]

IIRC it was Smokey that mentioned it's entirely possible to pump water through a block too quickly- it fails to pick up as much heat as it should. That is why removing thermostats altogether doesn't necessarily solve overheat problems.

[roflwaffle]

This link pegs the efficiency increase from an electrical WP at ~5-10+% w/ a car that gets ~27mpg. Even w/ HD diesel running at 60+% load there's a benefit but it's really small, less than a percent. Most of the advantage seems to come from not running the system when it isn't needed. Not having to remove a ****-ton of belts, reservoirs, and an engine mount would be a double bonus IMO (Camry needs a new WP)!