Changing coolant circulation pump assembly...
 

Ok, so my CCU said my coolant circulation pump was faulty. I cleared out all the codes and this still came back up. I checked today with direct battery and it does not work.

I picked up a working replacement assembly from a local salvage yard, pump works fine, and I want to install it, here's the deal, am I going to have a coolant purge if I try to do this without draining the system? I'm tempted to try and do the install without draining off coolant but if it's going to create a mess I'll just drain down and flush the system and replaced the coolant. I suspect that it should be replaced anyway.

The pump is pretty high up in the system but there are five hoses connecting to the assembly so that's a lot of moving around to do before it's buttoned up again. Also there's the likelihood of introducing air into the system as well.

Thanks
Steve A

It shouldn't be a big issue. A little air from replacing the pump isn't worse than draining the whole system. When you button it up, run the car to operatinng temp, turn on the heat and it should purge itself of air as you drive. You aren't going to get so much air in that the car is in danger of overheating. The air will purge through the overflow and the engine will intake coolant as it cools off.

Thanks for the comment, I may try and drain off the overflow tank since I think that sits at about the same height as the coolant circ pump assembly. That way it might draw down below the level of the pump and I won't have any coolant loss while installing the pump.

Thanks
Steve a

How do you drain the overflow tank? Isn't it easier to connect a hose to the radiator drain and collect coolant into a clean container? As you said, you only have to get coolant below the level of the aux pump. You can see the level in the reservoir.

Where is the aux pump in a W140? I don't remember seeing it in my 93. I think cars with separate rear ACC have yet another pump in the right fender cavity.

Sixto
87 300D

I plan to just pull the hose off the bottom of the reservoir after I've removed it from the bracket, there's plenty of room to collect coolant from the hose attachment there I think. Alternatively I could drain off the radiator directly although I'm not sure how much that will pull down the reservoir.

The coolant circulation pump is under the driver side removable plastic cover, right next to where the AC low pressure attachment is. My car doesn't have rear heat / AC so I can't comment on that but the circ pump and solenoids are located there.

I'm not going to do this right now because I may couple the pump replacement with a full cooling system flush since I don't know when the coolant was last done and it could need it.

Steve A

Draining the reservoir is messy because you're dealing with the reservoir draining and coolant in the engine backflowing through the hose. You have to collect everything because there's no easy way to stop the flow until you reach a certain level. Draining the radiator is easy because there's a petcock with a small nipple. Open the petcock, watch the level in the reservoir, close the petcock when you've drained enough. No mess, no guessing. Not much guessing, anyway.

Sixto
87 300D

I dealt with this today, it didn't take as long as I thought it would but I followed sixto's advice and drained off the petcock port, which because of the design, was very easy to accomplish. It also let me consider the quality of my existing coolant, which appears to be a combination of mostly MB but with some green thrown in...yuck.

At any rate the AC compressor is replaced, the circ pump has been replaced, the CCU error codes erased and I think we can close the book on the AC problems. It works amazingly well and to be honest I was surprised that it didn't have an evap housing problem given the propensity for W140's to have evap problems...expensive evap problems!

The circ pump assembly was a pain to reinstall, I opted to replace the whole assembly rather than just the pump, I acquired a used one from a newer W140 that seemed in good working order. But with five hoses to attach in tight quarters it was a little bit of a fight.

At any rate, it's done and all is well...except for the coolant, which since it appears to be tainted, will have to be flushed and refilled. I found that the only place to buy the Zerex G-05 in full strength (not 50/50) is at Napa for $12.29 / gallon, Autozone here doesn't carry it any more. Fortunately they have plenty.

Steve A