D5 pump seems weak

I've been running an Aquacomputer integrated D5 pump for about 3 years. I've never paid much attention to the flow rate, but I always just assumed it was working well.

My old 7970 shit itself out of the blue though, which prompted me to overhaul the loop. Over the last few days, I've been trying to get the damn thing to prime, without much luck. So I've begun to tear it down, and it seems like the pump will just barely move water. I've pressurized the intake line from the faucet to try to flush any air out, but once I remove the inlet pressure, the pump will just barely sustain flow. About a 6" pressure head on the outlet is enough to stall it.

This one looks pretty rudimentary, with no USB control, but a pot on the back of it. I've verified it's getting 12 volts. The magnet seems to be coupled strongly, and I guess it spins fast, but I don't really have a reference to go by.

On thing that is suspect is that this thing happily runs full speed in air, nearly silently. From what I've read, the bearing surface will howl if it runs dry.

Any suggestions? From what I'm seeing on YouTube, this pump should be flowing like a garden hose.

The pump is running full tilt in all of these pics:

I'd suspect the pump is just old.

Since you have the whole system apart, it can't hurt to replace it. Pumps are relatively cheap.

sounds like the pump is wore out tho i would think a d5 would last longer my mcp655-b is 5 years old and still working.

I guess I'll bit the bullet and just order a new one, but just in case...

I just connect the pump molex to a PSU molex, right? Simple as that? There's not something special people do that's so obvious to everyone but me, that it doesn't get documented anywhere?

It's such a simple device, it seems like it would either work fine or not at all.

Wrecked Em said:

On thing that is suspect is that this thing happily runs full speed in air, nearly silently. From what I've read, the bearing surface will howl if it runs dry.

Click to expand...

I thought if you ran the pumps dry it would burn the bearing up?

Wrecked Em said:

I just connect the pump molex to a PSU molex, right? Simple as that? There's not something special people do that's so obvious to everyone but me, that it doesn't get documented anywhere?

Click to expand...

Have you verified that the pump is wired to 12V (pump red to molex yellow, black to black) and not 5V (pump red to molex red, black to black) or 7V (pump red to molex yellow, pump black to molex red)? Tried rotating the speed control back and forth a few times to "clean" it?

If it wasn't completely wore out before, it likely is after running it dry in the bottom picture......time for a new one.

That rad also looks like it would be a little restrictive with the pump mounted on the side??

Time to replace it. Could be the volute or impeller are fouled, or the shaft is slipping, or the bearing is failed, I don't know exactly how a D5 is constructed. Likely, though, any of the usual suspects require complete disassembly, and in the reassembly of the unit, something is going to start leaking. The last pic looks like you've already tore it apart.

It shouldn't have any issue at all priming if you've pushed water through it with the faucet and it's not air bound, and yeah, it should be going like a water hose. So yeah, it's dead.

Confirmed. New pump is a night and day difference. Strange because based on the hum pitch, I'd estimate both pumps turning at about the same rpm. The new one immediately started sucking water though.

I ended up ordering a new top also because I wasn't sure if the integrated radiator was the problem. I'll probably re do my layout with the new pump separate at the bottom, and pull the impeller out of the old one and use it as a plug.

Thanks everyone.

that sucks but good you got it working right now.

Grats on the new pump. That is really wacky though. Pumps usually get old and die. Do you think there is any electrical damage to the pumps electrics?

Getting there:



I'd rip into the old pump to troubleshoot it, but with the new layout with the pump down low, I need the old one to fill the hole in the radiator.