Water Pump Question - coolant overflowing after shutdown

[dds28]

I have a 95 e420 that has been experiencing what seems like symptoms of overheating even though the temp in Honolulu has been around 75- 80 degrees. I have noticed that when the car is idling in traffic esp. with A/C on, the coolant temp ranges between 95-105 repeatedly until the car starts to move. The high speed fan does come on when it hits 105. When the car is shut down, coolant overflows and drains from the wheel well.

Things I have done since the overflow. I have replaced the thermostat with OE MB part. I changed the hoses and checked for leaks. Coolant has no oil contamination. Radiator is 2 years old. Fan clutch seems to be working and is also 2 years old. I have been adding coolant and it seems like every time I think the level is correct when cold, when I shut off the car after it has been hot (above 95), the coolant reservoir starts to bubble and overflows.

Could the water pump be on its way out? I did buy one but have not changed it out. My mechanic seems to think that the pump if not leaking shouldn't fail. Not sure what I should do next. I'm tired of wiping the coolant off of the garage floor.

 

[gsxr]

Re: Water Pump Question

Coolant temps of 95-105C sitting in traffic in Hawai'i is not really abnormal... however, the coolant reservoir overflowing is NOT normal. I don't think the water pump is at fault if it isn't leaking, and if the engine temps stay under ~110C.

It sounds to me like the system is not remaining pressurized. First thing I would do is pressure-test the system to 20psi / 1.4 bar and see if it holds pressure; if not, find the leak and fix it. Second, if the radiator cap is not recent, replace it with new OE or OEM Reutter 1.4 bar cap. Based on your description I have a feeling the cap is faulty. If the plastic coolant reservoir is orginal, keep an eye on potential cracks/leaks, especially at the top/neck. If you do replace the tank, replace the level sensor at the same time with OE or OEM Hella.

 

[gerryvz]

This sounds like normal behavior to me, in hot and humid climates. It also sounds like your coolant has been over-filled, which is not a good thing. When the car is COLD, it should be filled up between the MAX and MIN marks on the coolant overflow tank.

105-110C is NOT overheating on these cars, particularly in hot/humid temps. It just means that the car is not moving and getting airflow across the radiator. In summers in Houston (90+F daily temps with 80-90% humidity) I routinely see 105-110C temps when sitting in traffic. As long as it immediately goes down to the 95-105C mark, you should be OK.

Your water pump sounds like it is operating as it should. Indeed, visible coolant weeping or leaking from the pump would indicate a need for replacement.

The fan clutch won't kick in unless the car is moving (or the engine is revved in neutral), and won't kick in until the car is at 2,500-3,000+ RPM and the ambient temperature engages it. You can easily hear the roar of the fan clutch once it engages. If you are moving, say on the freeway, you will hear it engage and dis-engage from time to time. If you are in stop-and-go traffic, you won't hear it engage.

Sounds like your secondary-speed fan is kicking on appropriately, as well. I think this should be around the 105-107C level. The low-speed fan should ALWAYS be on when the A/C is running.

A/C running, in my experience, adds 2-4 degrees Celsius to the indicated coolant temperature at the gauge, FYI.

It sounds like your overflow tank, and coolant recovery tank inside the fender, are too full. I'd do two things immediately:

- Remove the inner fender liner and drain that coolant recover tank inside the fender (when the car's engine is cool), and
- Get the level of the coolant in the expansion tank to the correct level

As a later "fix" if you continue to be uncomfortable with the operating temperature, which MAY or MAY NOT help:
- Replace the fan clutch with a factory MB unit. The procedure is well documented on this forum, though you may need to make a special tool (ground down Allen Key) if you do the job yourself. You'll also need to get or create a tool to hold the fan pulley from rotating, so that you can loosen the central Allen bolt that holds the fan to the hub.

EDIT: As Dave says, consider replacing the coolant expansion tank cap as well. I don't think that is the problem, because if the system wasn't developing proper pressure, you'd be borderline overheating your car at 105C.

I recommend only MB factory fan clutches for the M119 engines. I know they are expensive, but they have been re-worked by MB and generally operate properly. Earlier versions of the MB factory fan clutch (including the originally equipped ones) did not always operate as they should have - an unacknowledged design flaw by MB. Some are reporting success with ACM clutches, which are much cheaper (and require a longer shorter bolt than the factory clutch). YMMY with this.

These engines DO NOT like hot and humid climates, as I've found out living in south-central Texas for the last 8.5 years. When the weather cools down for the winter (about 3 months in the 50s-70s), the M119 is MUCH happier and runs MUCH cooler. I never noticed this dichotomy when I lived in the relatively cool year-round climate of the Pacific Northwest before going to Texas.

Good luck !!

Cheers,
Gerry

 

[samiam44]

Since ppl have already mentioned the radiator cap.


With a/c on- you mention high speed fan.

At that temperature, the low speed fan circuit should draw enough airflow over the radiator to prevent overheating. You have a bad connection/burnt up low speed fan resistor(my guess). Make sure the high speed fuse is good. Both should trigger and work.

Fan clutch might not be engaging- could be bad or need adjustment. But in 80F, I'm not sure it would ever engage or do much at idle conditions.

It wouldn't hurt to pull the radiator, clean the airflow side of the coils to remove debris and the condenser coil also.

Sound like a little TLC and a 1/2 day of your time.

 

[gsxr]

IMO the main item here is "the coolant reservoir starts to bubble and overflows" after shutdown. That ain't right. Sounds to me like boiling, which should not happen if the system is properly pressurized.

Dumb question, but what is the ratio of antifreeze vs water? Even in a warm climate you still want at least ~20% antifreeze to increase the boil point and lubricate the water pump.

 

[samiam44]

I don't think he should be hitting high temp fan @80f

 

[gsxr]

I don't think he should be hitting high temp fan @80f

High humidity doesn't help; and he did say it was idling in traffic with AC on. Ideally it would not trigger the high speed fan but clearly something isn't ideal here. Also, if a "Cool Harness" is present, that will trigger the high speed fans at ±95°C, much earlier than factory.

Which reminds me - the OP needs to confirm that the LOW speed fans are running with the AC on. If not, that isn't helping operating temps either... but would still not explain the boilover post-shutdown.

 

[gerryvz]

The high speed fan does come on when it hits 105.

I don't think he should be hitting high temp fan @80f

High humidity doesn't help; and he did say it was idling in traffic with AC on. Ideally it would not trigger the high speed fan but clearly something isn't ideal here.

He said that he is triggering high-speed fan at 105C, which is about normal. When sitting at a traffic light, with A/C on, it is not unusual whatsoever for high-speed fan to trigger in hot temps and when coolant temp climbs >105C.

Also, if a "Cool Harness" is present, that will trigger the high speed fans at ±95°C, much earlier than factory.

There's no indication that a CoolHarness is present, though this should be checked. As should visual indication of low-speed fan operation, but I'd surmise from what he says that low-speed fan is indeed operating.

Low-speed fan should always be on when A/C is in operation. High-speed fan should engage around 105-110C (indicated on gauge)

The fan operation sounds normal to me, based on his description.

 

[samiam44]

I'll say it again-

Think he needs to check the low speed fan. With a/c on, it takes care of it and the temp is 85-95 c. This is a common problem on these W124.036/034 cars and he didn't say it was operating and if he's not benz familar- he might not even realize that the fan had 2 speeds.



M

 

[dds28]

Thank you everyone for the replies. The radiator cap is about 2 years old and is an OE one from MB. I did notice that coolant does seem to seep out when it is boiling so I will change it again because I can here stuff leaking out of there. I took a video of it and will try to post it when it is bubbling. Also now that I think of it, I haven't heard the low speed fan in a while. I have already in the past replace the resistor and check the wires. It used to work. I replaced both the blue and the green relay with OE units as well. I guess I need to check the freon level. I am pretty certain there is no cool harness. The high speed fan comes on at 105.

Coolant mix is about 50/50 with the zero g-05. Although now its been refilled so many times I am pretty sure it needs to be flushed. I will pressure check the system. I will also make sure that I don't overfill the system which I may be doing, but definitely that boiling-bubbling of the coolant is troublesome.

David

 

[dds28]

Here is the video of the leaking. I have unplugged the coolant level sensor for the time being. I changed to a new one (Hella) and need to still replace with new wiring plug.

[video=youtube;Wc0a7_ZZyHc]https://www.youtube.com/watch?v=Wc0a7_ZZyHc[/video]

 

[gsxr]

The boiling is not normal. When you have been topping off the system, are you using 50/50 mix, or plain water? I would still do a system pressure test as the next diagnostic. The reservoir has been replaced at some point, and the cap should be OK if it's that recent. I can see liquid and residue all over the reservoir tank and even splashed on to the air cleaner - wipe everything clean & dry, and try to pinpoint the source of the leak at the reservoir. Even when bubbling/boiling and going out the overflow, the tank should still be dry externally.

Side note - the correct fill level is at the seam of the tank when cold, to maybe 5mm above the seam at most. Photo attached.

 

[dds28]

I have been topping off with distilled water a few times and then 50/50 mix there after. I initially bought coolant from MB dealer without realizing that they changed to the blue stuff. The tank has splatter all over and is wet. I think perhaps I should change the reservoir tank. I will have the mechanic pressure test for me since I didn't see any visible leaks.

 

[nocfn]

left field for HNL, but does your heater work and if it does, does it work when traveling at higher speeds?

 

[samiam44]

FYI,

There is a second coolant tank-overflow in the fender well. I would plan on removing the liner and taking it out. Honestly, you should do both sides as debris tends to collect there and you don't want rust. Maybe the overflow hose is torn or leaking or the tank is bad. All 10mm and 8mm screws/nuts.
See what's going on- you can order the OEM braided hose or buy the internally braided style from MB. Probably be good to just replace the hose if you are going to the effort to get in there....
Other side has a hydraulic accumulator for the suspension and the bracket is known to rust out. Clean everything and worse case is remove the bracket, sand blast , prime and paint.

M

 

[gsxr]

Photo of the coolant overflow reservoir (yellow) and vacuum reservoir (white) located in the passenger fender well attached.

 

[gerryvz]

LOL! I mentioned clear back in Post #3 that he should remove and clean out the fender-inside-mounted coolant overflow tank as a first step, guys !!!

It sounds like your overflow tank, and coolant recovery tank inside the fender, are too full. I'd do two things immediately:

- Remove the inner fender liner and drain that coolant recover tank inside the fender (when the car's engine is cool), and
- Get the level of the coolant in the expansion tank to the correct level

 

[gsxr]

LOL! I mentioned clear back in Post #3 that he should remove and clean out the fender-inside-mounted coolant overflow tank as a first step, guys !!!

I agree, this is good maintenance, however the overflow is a symptom of the problem... not the root cause. Still need to figure out why the liquid is boiling / bubbling in the reservoir after shutdown.

 

[Klink]

Well, unless the car was driven hard and fast in summer desert temperatures, left idling for a while, and then was switched off just in the instant before the high-speed auxiliary fans kicked in at around 105-110°C, nothing should be going into the tank. There may be an ocasional tiny bit of seepage past the pressure cap settling in the bottom of the overflow tank, but generally, unless the car was super hot and then switched off and allowed to heat soak, nothing should be coming out of the expansion tank. Fluid going past a good pressure cap with the engine running can for a only mean that there is an underlying malfunction...

 

[emerydc8]

For the better part of a year, I listened to a gurgling sound after shutting down my Camaro (5.7L). Initially, I thought it was from the gas tank, but on further troubleshooting, I found that coolant was getting past the radiator cap and back-flowing into the reservoir tank. The Camaro has the cap on the radiator itself and the recovery tank is vented to the atmosphere. It is normally only half full. The weird part is that I never lost any coolant -- It would just go into the recovery tank on shutdown and work its way back into the system while running. The fix was to replace the radiator cap.

I don't know if the gurgling noise was boiling coolant or just coolant that was bubbling into the reservoir from the bottom.

 

[dds28]

As a matter of fact, the heater doesn't work in my car. Not that I ever used it in Honolulu but I tried it and there is not heat. Would that be a problem I should try to resolve? Also, the passenger floor board is completely dry so no leaks there. I need to find out why the coolant is boiling/bubbling.

 

[dds28]

Well, unless the car was driven hard and fast in summer desert temperatures, left idling for a while, and then was switched off just in the instant before the high-speed auxiliary fans kicked in at around 105-110°C, nothing should be going into the tank. There may be an ocasional tiny bit of seepage past the pressure cap settling in the bottom of the overflow tank, but generally, unless the car was super hot and then switched off and allowed to heat soak, nothing should be coming out of the expansion tank. Fluid going past a good pressure cap with the engine running can for a only mean that there is an underlying malfunction...

The temperature on my car has never exceed 105. Should I be worried a failed head gaskets? My car only has 66k miles.

 

[nocfn]

As a matter of fact, the heater doesn't work in my car. Not that I ever used it in Honolulu but I tried it and there is not heat. Would that be a problem I should try to resolve? Also, the passenger floor board is completely dry so no leaks there. I need to find out why the coolant is boiling/bubbling.

Well I suspected that. The auxiliary water pump for low speeds keeps the fluids flowing at low speed, and I suspected either air or a blockage in your system stemming from a rarely or never used heating system. On the W126, it is suggested to run the heater to keep corrosion down and the heater core protected. Now that may be a wives tale, but I run the heaters for a but t keep things flowing. Your system is full and continues to overflow makes me wonder abut full flowing system and bad aux pump, air block in core and the system needs t be bled or burped, investigate aux pump and drain fender overflow tank. More technical folks can chime in as to the plausibility of the idea.

 

[gsxr]

The temperature on my car has never exceed 105. Should I be worried a failed head gaskets? My car only has 66k miles.

If you are not mixing oil+coolant, I wouldn't worry about head gasket failure. Even temps on the wrong side of 120C may not kill the head gaskets. The M119 is amazingly robust.

 

[Klink]

The temperature on my car has never exceed 105. Should I be worried a failed head gaskets? My car only has 66k miles.

No.