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Discussion Starter · #1 ·
Can someone tell me how the Auxiliary water pump helps the cooling system--I use it to fill my system after flushing the coolent or when replacing the cooling system. It's great to do because you don't have to turn the engine on. But I don't know what it's function is besides that.
Just found out that mine isn't working for some reason and thinking this might have soemthing to do with the engine getting warm to a point that would thin out my oil and cause the pressure light to flicker
 

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The aux water pump helps to circulate coolant through the heater core when the car is moving slowly, or stopped. I suppose it can be used to help bleed air from the cooling system.

I believe I've already suggested to you, in another post, to measure the actual oil pressure at the oil filter canister.

You may have a defective switch, too thin oil, or a worn-out engine or oil pump.
 

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all it does is pump coolant to the heater core from the motor. there is 1 pump and 2 valve...one valve is for the passenger side the other for the driver side. If you remove it and replace with a "Y" or "T" fitting you will still have heat but will be hot all the time (when engine runs) and you will not have circulating coolant when off. It is true that on a hot day running the heater will help cool the coolant. Engine on or off this will circulate coolant. Check the KTMP on the OBC if it within range it is unlikely that this is your problem. Also, you should not need this to keep coolant at a good temperature...it can help reduce over heating, to turn on the heat, but that would just be treating a symptom not the problem. With or with out this the car should not leave normal range.
 

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The aux water pump helps to circulate coolant through the heater core when the car is moving slowly, or stopped. I suppose it can be used to help bleed air from the cooling system.

I believe I've already suggested to you, in another post, to measure the actual oil pressure at the oil filter canister.

You may have a defective switch, too thin oil, or a worn-out engine or oil pump.
an oil pressure gauge should screw right in where the switch is located to measure oil...I believe 50 psi is good and maybe going down as far as 20-30 at idle...and up to maybe 60-70 at high rpms.
 

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The control pressure (via relief valve in the pump) is 65 psi. A good engine and pump will always maintain this pressure at speed.

The switch closes at about 7 psi.
 

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WDS describes that the auxillary water pump provides additional flow through the cabin heater core when the engine drive pump doesn't provide much heating, i.e. at idle RPM. The intent is to maintain cabin heating in slow traffic. Consistent with the instructions to ensure that the HVAC system is in heating mode when bleeding the cooling system, i.e. to force the auxillary pump to run mode.

Given the curves of viscosity vs temperature or engine oil, I doubt that oil would become so thin as to cause low pressure without causing an overtemp warning. Further, there have been a number of posts describing inop auxillary water pumps with no mention of oil pressure warnings. I'm afraid you have another problem. :cry:

I'd try a new oil pressure sender or an oil pressure check on a hot engine with a stand alone gauge. I'll cross my fingers for you.

EDIT: I guess I wrote too slowly & got distracted by SWMBO. There were no replies when I started. Sorry, I didn't intend to duplicate the advice in posts above.
 

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Discussion Starter · #7 ·
Edjack--I'm checking the iol pressure this week to make sure of what's going on. I have a new pressure switch installed now--did that about a month ago--I also installed a new Cap on the oil filter with new rings, As previous, the light doesn't come on or even flicker when I drive without the AC on--even in the high 90% heat. The only time it comes on is at idle and when the AC is turned on. As before I'm noticing that the RPM's fall just a little at idle when I cut the AC on--they should rise--instead the fall--The engine has many mile on her , indeed--just trying to find away to keep her running without giong through a rebuild--if it comes to that--I have my eyes on a 530 engine to drop in where the 525 is currently housed
 

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I believe the purpose of the aux water pump is to provide water flow through the engine core during the residual heat mode. If you don't use this mode, having a dead one shouldn't matter.


From the User Manual:

Residual Heating Mode
The heat which is stored in the engine is utilized for heating the interior when the engine has been switched off (while waiting at a railroad crossing, for instance). In ignition key position 1, you can alter the settings of the automatic climate control. In ignition key position 0, the system automatically directs heated air to the windshield, side windows and footwells. This function is available for operation when the outside temperature is below approximately 59 7 (15 6), with the engine warm from recent operation and an adequate charge in the battery. The LED on the button will light up when all conditions have been met.
 

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As previous said:
The RPM falling at idle with the AC on indicates that the idle control valve is bad. I'm pretty sure your engine has one. If so, have you ever cleaned it?
My 540 hot oil pressure at 550RPM idle is only 10PSI, with the AC on (700RPM) it's up to 20+PSI.
 

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Discussion Starter · #11 · (Edited)
I clean the idle control valve about every 6 months. It's been a 3 since the last cleaning. It was spotless on the last cleaning and the car purrs like a kitten when at idle. It idles so well you have to look at the tach when the windows are up so you can tell it's running, when at idle.
I have noticed that at start up when the engine is cold the RPM reading are around 850 to 900 RPM when the engine is cold and the engine at start up is smooth at idle as well as when warm.
 

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What does "it's been a 3 since the last cleaning" mean?
Still the idle shouldn't drop when the AC is on. I'd bet that is the root of your problem.
 

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Discussion Starter · #13 ·
I didn't queit read what I had printed Jim--I ment that it's been 3 months since the last time I cleaned the ICV. On the RPM drop--yep that doesn't sound right at all---the Compressor is not giving me any trouble--it's nice and queit--I read the other day where a gent had the same problem and that there was indeed a fault that he and his indy had found and corrected when they interfaced the OBC There was supposed to be a setting that when the AC was turned on the RPM was indeed supposed to rise-his was doing the same as mine--it was decreasing insted. They corrected the problem by someway in the interface by adding 100 rpm and all was well afterwards. If my car starts and idles well at 850 to 900 when cold--that tells me my ICV is Ok--I think it is anyway---Thanks for the input.
 

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If cold idle is OK then the ICV should be doing it's job. I'm not sure what is used to bump it up when the AC is switched on. Maybe the DME tells the ICV to open up more and that's not happening??
A friend had a similar problem with his 540 (M62tu) when he turned on the headlights, his alternator light would flicker. He had the water cooled alt replaced and still had the same problem.
I looked at the alt output at idle and it was borderline OK. I told him to go back to the dealer and have them set the idle speed a bit higher, after that it was OK.
 

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Discussion Starter · #15 ·
OK--I just unlocked the OBC and found that when at idle and the car heated up I have 720 or so RPM--the idle went from 712 --to 725--to 720 and floated around a bit, but you couldn't feel it in the car. When I turned on the AC the idle went to 725--to 735--to 74- back to 725 and such as that--but everthing again felt stable inside the car-I couldn't see the needle move around any, but the digital information gave me numbers that tell me that the engine does idle just a few more RPM's when the AC is turned on--but not by much
 
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