How to bypass auxilary water pump?

**davidre391** · 09-22-2018, 12:12 AM

my car is a 1998 540i manual. The aux water pump is leaking and i want to know how i can temporarily bypass it? i should have my new pump in a few weeks but until then i need to drive this car to go to work. I notice there is a hose coming from the back of the passenger side head and going to the pump then there are 2 hoses at the top of the pump going somewhere else, but which hoses do i connect together??

**davidre391** · 09-22-2018, 12:13 AM

my car is a 1998 540i manual. The aux water pump is leaking and i want to know how i can temporarily bypass it? i should have my new pump in a few weeks but until then i need to drive this car to go to work. I notice there is a hose coming from the back of the passenger side head and going to the pump then there are 2 hoses at the top of the pump going somewhere else, but which hoses do i connect together??

https://www.realoem.com/bmw/enUS/sho...diagId=64_0994

**davidre391** · 09-22-2018, 12:23 AM

can someone please point out which hoses to connect to bypass the aux water pump , and also which hoses would bypass the heater core? thank you very much i really do appreciate the help.

**Santaclaus4** · 09-22-2018, 01:03 AM

If you take the valve and pump assembly out of the loop (car) and simply connect the hoses together, you're gonna have full heat and you won't be able to modulate it very much. You are gonna get "toasty". If you simply "cap and stow" the hoses, you won't have any heat.
How bad is it leaking? Is it just seeping with an occasional drip, or is it a trickle?
Just wondering if you could let it be for now.
Btw, when you disconnect the hoses to replace it, hardly any coolant will come out. When I replaced mine a few weeks ago, I didn't even have to add coolant when I was done.

**JimLev** · 09-22-2018, 06:43 AM

Post at 10:12, 10:13, 10:23 looking for an instant answer? Chill.

Hook hose 5 to hose 12.

**geargrinder** · 09-22-2018, 08:08 AM

Why would it ever take a few weeks to get a new pump? Financial reasons? I'd just whack a new one in there right away, or, try to find a cheap junkyard one as a stopgap, or, worst case... as mentioned keep driving and adding coolant if the leak is minor.

**davidre391** · 09-22-2018, 09:28 PM

thank you , so looks like connecting 5 to 12 would bypass the pump yes, but how could i still have heat? i was thinking if i connected 5 to 9 and then 8 to 12 i would still have heat but bypass the pump?

yes, financial reasons at the moment and its leaking pretty bad. which hoses would you connect together to simply bypass just the pump?

**shogun** · 09-22-2018, 10:14 PM

you still will get heat when the heater is on. The aux water pump just works independent from the main water pump, as it is electric driven and pumps per hour abt. 900 ltr into the heater core, no matter what the RPM of the engine is.

**Santaclaus4** · 09-23-2018, 12:56 AM

Originally Posted by shogun

you still will get heat when the heater is on. The aux water pump just works independent from the main water pump, as it is electric driven and pumps per hour abt. 900 ltr into the heater core, no matter what the RPM of the engine is.

I believe the hot water goes from the aux pump, through to the heat control valves. If the aux pump is "capped off", how is hot water gonna get to the heat control valves and eventually the heater core? If the lines are connected together (bypassing the aux pump and heat control valve assembly) it seems like he's gonna get an uncontrollable (or at least barely controllable) heat condition in the cabin.

**shogun** · 09-23-2018, 01:08 AM

yes, but he want to have a cheap solution, and if he connects hose 5 to hose 8 or 9, only 1 side gets heat
08 Hose f water valve and right radiator 1 64218391017 (feed)
09 Hose f water valve and left radiator 1 64218367929 (feed)

https://www.realoem.com/bmw/enUS/sho...diagId=64_0994
In case he connects hose 5 with 12, the heater core is by-passed, no heat at all.
If he wants to heave heat on both sides, he has to use a y-tube and connect 5 to 8 and 9. To control the heat the cheap way, a water shut off valve from the plumper will do.

On the E32, E31, E34 it is easier, there aux water pump has an inlet hose and a outlet hose, the outlet hose goes to the heater valves, so when by-passing the aux water pump on these cars, both sides get heat, as it goes into feed line heater valves, but on E39 not possible, see drawing

**demetk** · 09-23-2018, 09:40 AM

How much are you guys buying these for? I see an oem valve is like $450? And do you actually need the aux pump? You can buy a valve without the built in aux pump for around $80.

**geargrinder** · 09-23-2018, 10:06 AM

somebody once said:

Originally Posted by geargrinder

Why would it ever take a few weeks to get a new pump? Financial reasons? I'd just whack a new one in there right away, or, try to find a cheap junkyard one as a stopgap, or, worst case... as mentioned keep driving and adding coolant if the leak is minor.

**pleiades** · 09-23-2018, 12:11 PM

davidre391, is it actually the pump that's leaking, or a hose that's connected to the pump?

**1999 540i m** · 09-23-2018, 12:22 PM

Originally Posted by demetk

How much are you guys buying these for? I see an oem valve is like $450? And do you actually need the aux pump? You can buy a valve without the built in aux pump for around $80.

I used the control valve from a X5, no pump works great

**demetk** · 09-23-2018, 12:58 PM

Originally Posted by 1999 540i m

I used the control valve from a X5, no pump works great

Thanks. It's good to know I can use the one without the pump.

**TerraPhantm** · 09-23-2018, 01:28 PM

Originally Posted by Santaclaus4

I believe the hot water goes from the aux pump, through to the heat control valves. If the aux pump is "capped off", how is hot water gonna get to the heat control valves and eventually the heater core? If the lines are connected together (bypassing the aux pump and heat control valve assembly) it seems like he's gonna get an uncontrollable (or at least barely controllable) heat condition in the cabin.

As long as he retains a valve, the heat will work and be controllable. The main thing that would be lost is the parked car ventilation which relies on the aux pump.

On some models that run lower coolant temperatures (most of BMW's diesels and M models), the aux pump also plays a role in getting heat to work more effectively (as evidenced by E46 diesels and M3s having an aux pump despite not having any parked car ventilation option).

**JimLev** · 09-23-2018, 03:05 PM

Without the pump he could have some issues purging the air out of the cabin heater box if he ever drained the system.

**davidre391** · 09-23-2018, 03:37 PM

Originally Posted by TerraPhantm

As long as he retains a valve, the heat will work and be controllable. The main thing that would be lost is the parked car ventilation which relies on the aux pump.

On some models that run lower coolant temperatures (most of BMW's diesels and M models), the aux pump also plays a role in getting heat to work more effectively (as evidenced by E46 diesels and M3s having an aux pump despite not having any parked car ventilation option).

im gonna try to bypass it later today temporarily by getting a T shaped valve at the hardware store. Does anyone know what size those hoses are? or approx size so i know what kind of valve to buy. The Lowes store near me has a prestone T valve that i could prob use.

**shogun** · 09-23-2018, 06:31 PM

you have to measure the diameter of the hoses, realoem does not mention hose dia., just the size of the hose clamps
06 Hose clamp L16-30 64218367179
07 Hose clamp L28-33 07129952113
10 Hose clamp L18-24 07129952109
11 Hose clamp L16-30 64218367179
13 Hose clamp L16-30 64218367179

This is the heater valve and aux pump for E34, E32, E31, there the aux pump is separately mounted and has an inlet and outlet which goes into the water valve feed, so much easier to by-pass http://bmwe32.masscom.net/johan/wate...e_and_pump.jpg
http://bmwe32.masscom.net/johan/wate..._and_pump2.jpg

**Santaclaus4** · 09-23-2018, 08:03 PM

Originally Posted by demetk

How much are you guys buying these for? I see an oem valve is like $450? And do you actually need the aux pump? You can buy a valve without the built in aux pump for around $80.

Yes, they really are that expensive. I just replaced mine a few weeks ago. After looking online I finally came to the conclusion it's just gonna be a spendy part and that's that. Now I probably won't have to worry about it for another 15 years.

**demetk** · 09-23-2018, 08:44 PM

Originally Posted by Santaclaus4

Yes, they really are that expensive. I just replaced mine a few weeks ago. After looking online I finally came to the conclusion it's just gonna be a spendy part and that's that. Now I probably won't have to worry about it for another 15 years.

Wouldn't it be nice if the parts of now are build to last as long as the parts of then? We should make a point of revisiting this thread in 15 years for an update.