190e 2.6 auxilliary water pump problem.

[Darin Darlingto]

Just bought a 1990 190e 2.6 from the local MB dealership in Bend, OR. Very nice car which they sold new and took back in on trade. 81,000 miles.

Problem: When I bought it, it had a leaky auxillary water pump (little pump over the passenger side fender well under the hood). As part of our purchase agreement, the dealership ordered a new pump and installed it for me. Once the new pump was plugged in, I lost all power to my climate control system, which was working properly with the old leaky pump. When the new pump was unplugged, everything started working again. The service dept. determined that the new pump's wiring must be bad, so they ordered another one. When the second new pump arrived, it did the same thing. The service manager explained to me that I must have some sort of electrical problem in my climate control wiring that is causing it to shut down when the auxillary water pump is plugged in. He said that it could take some time (and of course $ in labor) to track down the problem and since the system works fine without the auxilliary pump, to just keep it unplugged until I have the money to fix it, or track it down myself. (it should also be noted that the car has a brand new main water pump and thermostat which seem to be keeping everything running ok, even without the help of the auxilliary water pump). The service manager told me that as the weather warms up this summer, I could experience overheating unless the auxilliary pump is working, although, he said it could continue to be fine without the auxilliary pump.

Question: First of all, do you have any idea what the problem is? Second, am I ok to keep driving the car, provided I always keep a close eye on the temperature. Any help you can give me on places to look or things to check which could save me shop labor hours would be very appreciated. This is my first MB and I am far from mechanically oriented, although my father is both a mechanic and electrician and is willing to help. No experience with MB cars, however.

[vinamg]

Where are you located? Unless you use the heater, the aux pump should not be causing any problems. The aux pump is only triggered when you turn on the heater. It is designed to circulate coolant through heater core during heater operation. It is in no way used to assist during idle operation (stationary car). The name is somewhat misleading and people get confused about its actual purpose.

As for the electrical problem, first check you charging system. Next try connecting old pump (electrical plug only) to check if it spins (make sure the heater is on). I'm guessing that it doesn't work at all and that you have a load problem. Measure the voltage at plug (heater on) you should be getting battery voltage.

Measure the following as well:
1. Aux pump current draw (around 1.3 amp)
2. Monovalve resistance (11-19ohms)

If everything checks out you might have a problem with the pushbutton control unit.

Good luck.

Vin

[Jim Anderson]

It sounds like you have a bad power connection to the climate control, probably its ground. It's good enough for the relativly low current draw of the climate control but not enough for for the relatively high current draw of the pump. Double check your old pump, I'll bet it doesn't turn.


I heard the pump will come on when the engine is turned off and is hot to cool it down. Anybody know if a 190e does that?

[Darin Darlingto]

Thanks for everyone's input. It's been very helpful. Here is an update on the problem:

I wish I had the old pump, but unfortunately, the MB shop threw it away when they installed the new one.

First of all, I have tested the new pump and it works fine.

Second, I can get the new pump and climate control system to work, but it takes several tries of turning the car off and on, each time resetting some sort of breaker/circuit. Once the system is running, it will keep running until the pump shuts itself off when the system reaches the proper temperature. Climate control system then keeps working until the pump tries to come on again (under the start-up electrical load), at which time the breaker/circuit trips and the whole system shuts down. I can keep the system running indefinitely if I keep the temperature dial set to maximum temperature, thus keeping the aux. pump running all the time and avoiding the start-up load. The problem with that is obvious, TOO HOT!

Based on these findings, start-up load appears to be the problem. The operating load of the aux. pump is around .9 amps and the start-up load is 1.2 to 1.3 amps. This appears to be within the perameters.

This brings me to a couple of questions:

1. If the start-up load is normal, then could it be that the breaker/circuit is no longer handling the load? If so, does anyone know where this breaker is located?

2. Although the new pump looks similar to the old pump, it is lightly different. Could it be that the new pump draws more power than the old one did, thus causing my problem?

Input from anyone would be appreciated.

[Billybob]

Do search of threads on this issue, the failure of the auxilliary pump can fry electronic components and the circuit board's traces on the CC unit. Maybe this has already happened from the earlier motor failure? Commom concensious is insallation of an inline fuse for the pump is cheap insurance to protect the costly CC unit.

You can check these guys out for some info also:

http://www.fix.net/~gdl/begin1.html