Dnk Posted June 21, 2017 Share Posted June 21, 2017 Trying to find out what a 3.9 litre V8 water pump flow rate should be at tickover I'm reading a base guide is 1/3 of the horsepower = the Litre per minute flow rate For example a 300 hp supra should have 100 litres per minute flow rate which seems high to my mind as that's 1.6 litres per second !! Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted June 21, 2017 Share Posted June 21, 2017 Shut the heater matrix flow off, take top rad hose off, block top rad hose stub, garden hose in filler neck, idle engine put bucket under top hose for five seconds, measure volume of contents, get pencil and paper, do the maths Electric water pump specs show flow rates, find one for a similar engine size and see what they flow as a rough guide? Quote Link to comment Share on other sites More sharing options...
rider Posted June 21, 2017 Share Posted June 21, 2017 There is a figure offered up by someone, likely an American. "around 0.2 usgpm/bhp at max revs." For your setup that'd be more like 200l/min which equates to around 30cc per pump cycle which doesn't sound unreasonable. Quote Link to comment Share on other sites More sharing options...
rider Posted June 21, 2017 Share Posted June 21, 2017 A typical water pump can move a maximum of about 7,500 gallons (28,000 liters) of coolant per hour, or recirculate the coolant in the engine over 20 times per minute. This means that a water pump could be used to empty a typical private swimming pool in an hour! The slower the engine speed, the less power is consumed by the water pump. However, even at 35 mph (56 km/h), the typical water pump still moves about 2,000 gallons (7,500 liters) per hour or 0.5 gallon (2 liters) per second! Quote Link to comment Share on other sites More sharing options...
Dnk Posted June 21, 2017 Author Share Posted June 21, 2017 I was trying to get an idea without doing all that but yes that is the most accurate way for sure. The owner has done a visual test running the coolant into a plastic bottle at tickover and the flow looks rather tame, definitely not 1 litre per second He's bought this with lots of work done, skimmed heads, head gaskets, thermostat, hoses, water pump. He's since done a pressure test, ok, sniff test ok, replaced thermostat. It trys to overheat but without the stat in it runs cooler with no issues, the water pump isn't OE hence me thinking perhaps its not flowing enough once the stats in or is that bollocks lol Quote Link to comment Share on other sites More sharing options...
Dnk Posted June 21, 2017 Author Share Posted June 21, 2017 The video of the test the owner did https://www.facebook.com/shane.sawatzki/videos/1502228576494187/ Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted June 21, 2017 Share Posted June 21, 2017 about 120 litres per minute at whatever RPM the pump is most efficient at. at engine max RPM most pumps are not going to flow as much as at max torque RPM where most heat is generated. i think the electric pumps for circa 3 litre petrol engines flow about 110 to 130 litres per min. Diesel engines are not a good comparison as far more fuel energy goes into torque and not heat. - - - Updated - - - Bear in mind if the stat is not fully open most water will recirculate in the block / heads. Quote Link to comment Share on other sites More sharing options...
Dnk Posted June 21, 2017 Author Share Posted June 21, 2017 Cheers Chris He says he's tried 3 stats now with the same result Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted June 21, 2017 Share Posted June 21, 2017 Well what's the issue, is it overheating? Quote Link to comment Share on other sites More sharing options...
Dnk Posted June 21, 2017 Author Share Posted June 21, 2017 Taken from the guys post on f/b The issue I am having is at idle/not moving the heater will slowly stop blowing heat and if I don't rev the engine the temp gauge will begin to rise, however I can hold RPM at 1000 rpm and I will maintain heat and the temp gauge will sit just below half and I can do this forever , I sat in the driveway holding 1000 rpm for more than 30 minutes straight and didn't lose heat, as soon as i let it idle , within 4 minutes of idling the heat slowly goes away and temp gauge eventually starts climbing but it won't overheat , the gauge will make it to the top of the white and fall back down to normal I am stumped ! Quote Link to comment Share on other sites More sharing options...
Digsy Posted June 21, 2017 Share Posted June 21, 2017 about 120 litres per minute at whatever RPM the pump is most efficient at. at engine max RPM most pumps are not going to flow as much as at max torque RPM where most heat is generated. i think the electric pumps for circa 3 litre petrol engines flow about 110 to 130 litres per min. I'm always very wary of comparing flow figures for electric water pumps with mechanical pumps, as the electric pump manufacturers tend to state the flow at practically zero head. The Davies Craig EWP80, for example, will only flow 80 litres per minute against a maximum of 7.5kPa head. The resistance in an engine cooling system can easily be ten times that. Mechanical pumps have a lot more "oomph" and can flow against a much higher system restriction. OE engines which use electric water pumps like BMW, Volvo and Toyota have their cooling system specially engineered to suit. In fact, I don't really understand how aftermarket electric pumps work at all, as the end user typically will not have access to any of the measurements required to determine if the pump is correctly sized or not. There are no hard and fast rules but a gasoline engine will normally reject about 50% of brake power to coolant at full load / max speed. More if the engine has other water cooled items like turbos, water-oil coolers, cooled EGR, etc, etc. Typically,the pump will be sized so that the difference between bottom and top hose temperatures is about 8 degrees with a fully open thermostat. You can use the schoolboy physics formula Q=m.Cp.DeltaT to work out the required flow. Q = heat flux (in this case 50% - or whatever factor you want to use - of brake power, in Watts). m = mass flow rate of coolant in kg per second (approx 0.0167 kg per second = 1 litre per minute) Cp = specific heat capacity of coolant (about 3600 J/kg.K for 50/50 water / glycol) DeltaT = the temperature rise in degrees C or K So for the 300hp Supra example: Q = 60% (let's say, allowing for turbos and oil cooler) of 300hp = 0.6 x 223.71kW = 134226W Cp = 3600 J/kg.K DeltaT = 8K Q = m.Cp.deltaT , so m = Q / (Cp.deltaT ) m = 134226 / (3600 x 8) = 4.66kg/s mass flow rate 4.66 / 0.167 = 279 litres per minute at full chat. Quote Link to comment Share on other sites More sharing options...
Dnk Posted June 22, 2017 Author Share Posted June 22, 2017 Found this whilst searching Quote Link to comment Share on other sites More sharing options...
Dnk Posted June 22, 2017 Author Share Posted June 22, 2017 I'm always very wary of comparing flow figures for electric water pumps with mechanical pumps, as the electric pump manufacturers tend to state the flow at practically zero head. The Davies Craig EWP80, for example, will only flow 80 litres per minute against a maximum of 7.5kPa head. The resistance in an engine cooling system can easily be ten times that. Mechanical pumps have a lot more "oomph" and can flow against a much higher system restriction. OE engines which use electric water pumps like BMW, Volvo and Toyota have their cooling system specially engineered to suit. In fact, I don't really understand how aftermarket electric pumps work at all, as the end user typically will not have access to any of the measurements required to determine if the pump is correctly sized or not. There are no hard and fast rules but a gasoline engine will normally reject about 50% of brake power to coolant at full load / max speed. More if the engine has other water cooled items like turbos, water-oil coolers, cooled EGR, etc, etc. Typically,the pump will be sized so that the difference between bottom and top hose temperatures is about 8 degrees with a fully open thermostat. You can use the schoolboy physics formula Q=m.Cp.DeltaT to work out the required flow. Q = heat flux (in this case 50% - or whatever factor you want to use - of brake power, in Watts). m = mass flow rate of coolant in kg per second (approx 0.0167 kg per second = 1 litre per minute) Cp = specific heat capacity of coolant (about 3600 J/kg.K for 50/50 water / glycol) DeltaT = the temperature rise in degrees C or K So for the 300hp Supra example: Q = 60% (let's say, allowing for turbos and oil cooler) of 300hp = 0.6 x 223.71kW = 134226W Cp = 3600 J/kg.K DeltaT = 8K Q = m.Cp.deltaT , so m = Q / (Cp.deltaT ) m = 134226 / (3600 x 8) = 4.66kg/s mass flow rate 4.66 / 0.167 = 279 litres per minute at full chat. 1 Gallon per second Quote Link to comment Share on other sites More sharing options...
Digsy Posted June 22, 2017 Share Posted June 22, 2017 1 Gallon per second Yes - but that calc is based on a lot of assumptions. However I did recently work on a fairly run of the mill turbo engine (140hp) which needed a pump capable of flowing about 150LPM at full chat, so the maths scales pretty well. Quote Link to comment Share on other sites More sharing options...
Dnk Posted June 23, 2017 Author Share Posted June 23, 2017 Yes - but that calc is based on a lot of assumptions. However I did recently work on a fairly run of the mill turbo engine (140hp) which needed a pump capable of flowing about 150LPM at full chat, so the maths scales pretty well. Thanks for the info Quote Link to comment Share on other sites More sharing options...
Wez Posted June 23, 2017 Share Posted June 23, 2017 Crikey that is some serious flow Quote Link to comment Share on other sites More sharing options...
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