What's the true purpose of the AUX coolant pump

[Blueberryyum02]

Changing out the DCCV, i studied the parts and the way each hose is routed, the feed line from the tee'd hose connects to the angled nipple on the DCCV, the down port of the aux circulation pump connects to the straight nipple directly under the what I assume to be the angled feed port, The side port of the aux circulation pump connects to the port on the side of the thermostat housing tower.

You have the two ports that feed hot coolant to the heater core.

Now under the heater core feed lines is the return port.

This what have me confused about this design. When sitting with the DCCV in hand looking through, the bottom port its a clear opening, which means the aux pump sends coolant back through the return port while the plungers open directing coolant through the heater feed lines.

The only separation between all of this is the the closed plungers. Which stops flow to the heater core.

Why is the return line from the heater core, directly open to the feed of the aux circulation pump? Which on would think even if the plungers are closed in the off position hot coolant can be forced back up the line by means of the return side of the heater core since it's a direct opening to the aux circulation pump With nothing obstructing it.

Can some please help me understand this cause I can't see or think of any other reason why this could or shouldn't be the case, if there's no separation of the two ports.

 

[RigsLS]

Although I didn't put as much thought into it as you currently have, the Auxiliary Coolant pump serves purpose to provide a consistant flow of hot coolant to the interior heater core during low RPM, at idle speed the system (from what I understand) does not have enough flow, therefore the pump provides additional flow to provide heat. It also plays a part in continuing the flow of coolant after engine shut down, in order to cool itself down.

The auxiliary coolant pump:

- provides heater coolant flow boost.
- has a secondary function of providing engine-off cooling.



Coolant Flow // Item #21 - Auxiliary coolant pump (2nd GEN)

The auxiliary coolant pump is declared faulty/defective/not working, when there is sufficient interior heat during higher RPM's but no heat during idle RPM's. In other words, when there is no heat from the vents during idle but lots of heat during driving speeds, it's time to replace the 12V BOSCH coolant pump.


Sorry, I do not have enough information with respect to all the plungers and passages, it just does it job as designed.

 

[FDR]

Is part #1 the DCCV? Is it mounted directly above the passenger sway bar bracket, covering the forward bolt entirely on a gen 1 V8?

 

[RigsLS]

Yes, on the first GEN the DCCV is positioned directly below the Auxiliary pump when looking straight down the condenser.
It is reversed from the second GEN which have the DCCV mounted above the Auxiliary pump.

On the first GEN the DCCV is at the very bottom and yes it is partially in the way of the sway bar bracket bolt/nut.

The DCCV is mounted on a bracket to the fan shrouding, the bottom bolt needs to be removed entirely but the top bolt needs to only be loosened, it hangs on the hooked bracket allowing it to be moved slightly out of the way for sway bar bushing replacement.

IIRC.

 

[Kumba]

The AUX pump is there to provide hot engine coolant to the DCCV regardless of what the thermostat is doing and to circulate coolant through the engine itself when cold. It is probably needed because the engine's water pump is internal and it was cheaper to have an aux pump with funky plumbing then cast in a set of coolant nipples on the block or the water pump. You also need to have coolant moving in the block when cold for it to thermally stabilize and the thermostat to work at all. If the coolant never circulates internally then the thermostat won't open up till it's too late. You'll end up with hot pockets in the block/head which is bad. You can boil off your coolant or cause thermal shock. Aluminum engines are very sensitive to thermal management. They aren't like old iron blocks where you can run them down the road with a radiator cap whistling in the wind impersonating a steam locomotive.

On your diagram you can see that the aux pump takes water from just before the thermostat, circulates it through the DCCV and cores, then it returns back to the hose that feed into the inlet side of the radiator. This means that when the pump is on it's circulating a small amount of coolant through the engine. The bypass hose on the Gen1 DCCV may be to ensure that coolant still circulates regardless of the DCCV state. In other words even if coolant isn't going through the heater cores, it's still circulating coolant in the engine. They changed the design on the Gen2 DCCV but I imagine it serves the same purpose.

Plus like bigrig said, they might be using the aux pump after shut down to do some additional cooling to the engine so it doesn't heat-soak too badly.

A lot of your older engines had an external water pump with connections for the heater core actually on the water pump for this purpose. That way the mechanical pump was always pumping hot engine coolant through the heater core regardless of what the thermostat was doing. The below picture is of a Ford 302 water pump. The pump is upside down but the nipples on the right side of the picture are for the heater core. One pushes out hot coolant from the engine block and the other is on the intake side of the pump which sucks it back in. Thus you create a small coolant loop to make sure the engine heats up uniformly when cold and that the thermostat has a chance to do it's job.

http://www.britishv8.org/articles/Images-V15-2/TechSession3-E.jpg

 

[Blueberryyum02]

The AUX pump is there to provide hot engine coolant to the DCCV regardless of what the thermostat is doing and to circulate coolant through the engine itself when cold. It is probably needed because the engine's water pump is internal and it was cheaper to have an aux pump with funky plumbing then cast in a set of coolant nipples on the block or the water pump. You also need to have coolant moving in the block when cold for it to thermally stabilize and the thermostat to work at all. If the coolant never circulates internally then the thermostat won't open up till it's too late. You'll end up with hot pockets in the block/head which is bad. You can boil off your coolant or cause thermal shock. Aluminum engines are very sensitive to thermal management. They aren't like old iron blocks where you can run them down the road with a radiator cap whistling in the wind impersonating a steam locomotive.

On your diagram you can see that the aux pump takes water from just before the thermostat, circulates it through the DCCV and cores, then it returns back to the hose that feed into the inlet side of the radiator. This means that when the pump is on it's circulating a small amount of coolant through the engine. The bypass hose on the Gen1 DCCV may be to ensure that coolant still circulates regardless of the DCCV state. In other words even if coolant isn't going through the heater cores, it's still circulating coolant in the engine. They changed the design on the Gen2 DCCV but I imagine it serves the same purpose.

Plus like bigrig said, they might be using the aux pump after shut down to do some additional cooling to the engine so it doesn't heat-soak too badly.

A lot of your older engines had an external water pump with connections for the heater core actually on the water pump for this purpose. That way the mechanical pump was always pumping hot engine coolant through the heater core regardless of what the thermostat was doing. The below picture is of a Ford 302 water pump. The pump is upside down but the nipples on the right side of the picture are for the heater core. One pushes out hot coolant from the engine block and the other is on the intake side of the pump which sucks it back in. Thus you create a small coolant loop to make sure the engine heats up uniformly when cold and that the thermostat has a chance to do it's job.

http://www.britishv8.org/articles/Images-V15-2/TechSession3-E.jpg

You just answered my question. Thank you. So instead of having the water pump do double duty it has a assistant which takes the load of heating the cabin and also provides a engine off way of cooling things down.

 

[Kumba]

You just answered my question. Thank you. So instead of having the water pump do double duty it has a assistant which takes the load of heating the cabin and also provides a engine off way of cooling things down.

The aux pump exists because it was cheaper then modifying the block, timing cover, water pump, or whatever else to provide that function. There really isn't a direct gain to having the aux pump as far as how the engine works or performs. If anything it's extra electrical load, more weight, and extra parts to go bad. But then again, they don't build a car to last forever. They just want it go get out of warranty.

I do not know if the pump stays on after you turn the engine off to provide some extra cooling to prevent heat-soak or not. You'd have to drive around for a while, crawl under the car, and have someone turn it off and listen for the pump running. Assuming it does do that, then there is your added benefit.

 

[Blueberryyum02]

The aux pump exists because it was cheaper then modifying the block, timing cover, water pump, or whatever else to provide that function. There really isn't a direct gain to having the aux pump as far as how the engine works or performs. If anything it's extra electrical load, more weight, and extra parts to go bad. But then again, they don't build a car to last forever. They just want it go get out of warranty.

I do not know if the pump stays on after you turn the engine off to provide some extra cooling to prevent heat-soak or not. You'd have to drive around for a while, crawl under the car, and have someone turn it off and listen for the pump running. Assuming it does do that, then there is your added benefit.

It runs when the car is off but it only comes on when the car is overheating. I think it's more so insurance for a bad design flaw when it comes to the cooling process. I have heard mines come on once or twice and that's when the engine was overheating due to a bad acuator from the fan. My opinion on it is it was a quick fix to a poorly designed coolant system. If you look at the water pumps today verses the ones from before they are smaller, you think by now they would have made a smaller water pump, that moved more water per second, I guess the tech involved out weighed the cost. So they added the electric pump to due what the smaller mechanical pump could not due. And that would be heat the cabin while maintain operating temps at low idle speeds.

What would have been a better connection to it is if it came on while the car was off and provided heat while in the accessory mode. That way you could be waiting on some one engine off saving gas and stay warm in the winter months.

That would have made more sense then just providing hot coolant at a stop light or low idle. Plus it would have alleviated the extra hoses, the routing of these hoses and so fourth. To just make a direct connection to the block.

 

[MIdsm]

My understanding of today's water pumps is a little bit different. In the past the common understanding was that more water being pushed through the engine means a cooler engine. Many people have found that the engine temps went up if a much larger pump was used or if a stock pump has been speeded up. Some racers slow down their water pump for a cooler angine - the engines run at elevated rpms for extended lengths of time. If the pump spins too fast it may cavitate. Also at higher engine rpm the pumping losses may outwighed the gains of a cooler engine. Just like anything else pumps have an optimum window of operation. Engineers have to figure out where that window is. The ls seems to be designed to compete with european sporty sedans. That means that it has to be able to run at extended speed and rpm for a long time. Also, the need for better fuel economy may lead to changes to optimal water pump design. The pump has to keep the car cool at idle and at speed in Death Valey heat or during you daily comute. Take a look at the torturous path the coolant has to take when going to and from the heater core. Every inch of hose length and every turn leads to pressure loses. If the engine water pump provides adequate water flow for cabin heat at elevated rpms but lacks a little performance at idle it may be appropriate to add another pump as the gains outweigh the losses. Packaging also leads to complications. Assembly as well. Longevity of parts also has a part in design of vehicles - look at the dccv - instead of sitting behind the engine and being baked by hot exhaust manifolds the dccv has been located in a relatively cool area with some fresh air. If the vehicle had a simple valve between the engine and the heater core and didn't have a dual zone heat, the aux pump probably wouldn't have been needed, but a luxury car has to have some amenities like dual air and heat.

If one looks at the above diagram the water flow through the pump is from dccv to the filler neck.

I do appologize for ramblling but i have been up for way too many hours today.

 

[Dugan]

Has anyone removed the auxillary coolant pump to confirm it it's actually needed for real world cooling or if it interferes with ecm operation?

 

[1LoudLS]

the way you know that you actually need one of these and its not a useless part just added to increase the cost of the car for no reason at all, because when it goes bad, there is not enough coolant flow when the car is just idling and you don't get any heat until the car starts moving and the RPMs get up and the main water pump starts making enough flow.

its not about needing it for real world proper engine cooling, its for real world heating.

 

[Dugan]

1LoudLS thank you very much for such a quick response sir, if I'm understanding you correctly then if heat isn't a concern for me, the only really useful function I would lose from deleting the aux is the defrost on cold mornings

So long as I keep the dccv and it is functional, the heat would work above idle and the car won't overheat?

All of this isn't of much concern until I replace the faulty controller in the console I'm sure...

 

[Gus_Mahn]

I had a piece of foil from an antifreeze jug stuck in my aux coolant pump suction. The only downside was no cabin heat at idle and low cruise. There was a little heat at expressway speeds, but way less than with the pump working properly. It's for cabin heat!

 

[Dugan]

Thank you Gus_Mahn for your reply, since im not concerned with a working heater at this point in the project I'm going to bypass the pump for the foreseeable future. I'm guessing with everything together and working the pump provides coolant to the heater core, and the climate controller tells the dccv how much coolant to allow to the heater core dependent on temp and blower settings from inside the cabin. I'm most likely going to swap in a 4.6 so I'll be able to delete all this stuff with the swap along with replacing the fan with electrics over hydraulic

 

[DeviLSh]

I deleted my Aux pump (and DCCV) on my LS, looping the lines to keep flow from degas back to rad hoses. No problems with overheating so far.

 

[Dugan]

So you have no heat with it back looped to the return hose or it's routed from return to heater core and straight back to rad?

 

[DeviLSh]

So you have no heat with it back looped to the return hose or it's routed from return to heater core and straight back to rad?

See post #17

I have no heat, so I removed 2/3 of the hardlines that feed the heater core. My degas returns to the port on the t-stat housing (genII). I am currently looking for an upper rad hose (silicone) from another car that doesnt have the large Tee in it. Since this is a fail point of the stock part, and mine is now capped. 1.5" ID needed, been looking around so far nothing thats the right dimensions.