How good is your water pump?

[dmcnc]

Hello everyone
How good is your water pump? I’m sure some of the old timers may know this, but in my endless quest for an optimized cooling system, I stumbled on the following:

Pump efficiency is directly related to the clearance between the impeller vanes and housing raceway. Considering standard clearance between impeller and housing is 0.75 ± 0.25 mm (0.030 ± 0.010 in), here are the measurements I came across an original water pump, an NOS water pump, and an aftermarket Volvo water pump.

1. Original Water Pump – Cast # 7941101660 , came off an original Delorean PRV crate engine with no miles on it. Clearance between housing and impeller vanes: 5.26mm (or 4.5mm in excess)

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2. NOS Water Pump - #07726-030; Clearance – 5.25mm (4.75mm over)

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3. Used aftermarket Volvo pump (20k miles) – (common replacement from one of the vendors); Clearance 4.48mm (3.73mm over)

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Here is where the impeller should be at 0.75mm

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A tight clearance ensures higher flow rates reduce the cycle time between the source and sink, especially at idle. Excess clearance reduces the amount of water under pressure that seeps around the impellers. Leakage at that point causes eddy flows and cavitation. For all the money we can spend on big radiators, electric fans, magic cooling fluid, we’re throwing away cooling efficiency if we’re not maximizing flow and pressure. Hope this drives good discussion and solutions.

[kings1527]

Where was the last pump in the post sourced from?

[dmcnc]

Where was the last pump in the post sourced from?

PJ Grady a few years ago. Intent isn't to call out any vendor; correct clearance seems to be the exception with these pumps.

[Bitsyncmaster]

Not sure how much pump flow affects the cooling of our system. The radiator and fans seem to be the most important.

[kings1527]

PJ Grady a few years ago. Intent isn't to call out any vendor; correct clearance seems to be the exception with these pumps.

That’s fine but my intent is to find out who’s offering the proper parts. If that means some vendors may be exposed as to offering a product that’s grossly out of spec, then that’s not my concern.

[David T]

While the clearance is important, IMHO it isn't the most important thing. Proper tension on the seal, the number of blades on the impeller and it's design, a lot of factors affect flow. Too much flow is also bad, the coolant needs enough time in contact to transfer the maximum amount of heat. No one is having problems with the pumps. The biggest problem is old hoses, pumps, seals and gaskets, followed by old radiators and old coolant. Then the old header bottle, bad "O" switch, fans not working, electrical problems, that kind of thing. "Slippage" in the water pump is WAY down on the list. With proper maintenance the cooling system is adequate. Using 30 + year old parts is not a good idea. BTW, how are you measuring that clearance?

[SBL]

David,

Would there be any advantage in using a thermostat that opens at a slightly lower temperature, say 10 deg F lower? Here today it was 93 in the shade and 107 on the blacktop. We never have ambient temps below 60 deg F at any time of the year. Anyway, with fans on continuously and AC on max, after 40 min stop and go driving, I hit 220 deg F (which I consider too hot). I would like to see if I could get that down by using a replacement thermostat that opened earlier, and was completely opened at a lower temp to try to ward this off. System is fully flushed etc. I have done this with other cars that ran a bit hot in South Florida summers, and it clearly helped. Obviously going too low is deleterious. Just thinking of a touch.

[DMC-Ron]

Would there be any advantage in using a thermostat that opens at a slightly lower temperature, say 10 deg F lower? Here today it was 93 in the shade and 107 on the blacktop. We never have ambient temps below 60 deg F at any time of the year. Anyway, with fans on continuously and AC on max, after 40 min stop and go driving, I hit 220 deg F (which I consider too hot). I would like to see if I could get that down by using a replacement thermostat that opened earlier, and was completely opened at a lower temp to try to ward this off. System is fully flushed etc. I have done this with other cars that ran a bit hot in South Florida summers, and it clearly helped. Obviously going too low is deleterious. Just thinking of a touch.

Normally your thermostat would be full open above 180+ unless you have a higher temp thermostat. But you can go to your favorite auto parts store and tell the clerk you need a thermostat for a 1985 Volvo 760 GLE 6-cylinder and pick the opening temperature you want (thanks to Farrar for the reference). Pick 170 if you want 10 degrees lower than stock. Given the heat in your area it certainly wouldn't hurt. Ultimately, thou, the upper temperatures that your talking about are an equilibrium between the radiator rejection and the engine generation with the thermostat at that point full open and not a factor. Better heat transfer with an aluminum radiator might be your best bet after verifying you're getting good air flow from both cooling fans.

Ron

[DMCVegas]

David,

Would there be any advantage in using a thermostat that opens at a slightly lower temperature, say 10 deg F lower? Here today it was 93 in the shade and 107 on the blacktop. We never have ambient temps below 60 deg F at any time of the year. Anyway, with fans on continuously and AC on max, after 40 min stop and go driving, I hit 220 deg F (which I consider too hot). I would like to see if I could get that down by using a replacement thermostat that opened earlier, and was completely opened at a lower temp to try to ward this off. System is fully flushed etc. I have done this with other cars that ran a bit hot in South Florida summers, and it clearly helped. Obviously going too low is deleterious. Just thinking of a touch.

No, there is no advantage. In fact, you will cause engine damage in the long-term with a lower temp thermostat.

Proper combustion inside of the chambers relies upon heat. Too cold of temperature results in a slower, and ultimately an incomplete burn. Aside from a slight bit of negative fuel economy, over time you will end up with severe carbon deposits on the piston and exhaust valves. The result is pre-detonation since carbon doesn't cool quickly, and eventually a loss of compression when the exhaust valves can't fully close due to the build-up.

Save for commercial trucks, manufacturers no longer place actual numbers on the temperature gauges for this very reason of drivers perceiving their vehicles as running too hot @ 220. It's the proper temp, and one that other vehicles run at. 235 starts to be the danger zone, but your car is running perfectly fine. Ask yourself why you "consider" this to be too hot of a temp.

Besides, you also have several feet of aluminum piping and hoses that also bleed heat off, aside from your radiator. Don't worry, your car is functioning normally.

[dmcnc]

BTW, how are you measuring that clearance?

I used the depth probe on a digital caliper on the measurements >1mm. I used a feeler gauge for the 0.75mm clearance. BTW, I didn't rebuild the water pump. I had it done through Flying Dutchman Water Pumps. They threw in new sealed bearings (original is open on the inside) and a modern style seal.