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2000 ML 430 - Cooling System - Running Hot

6K views 26 replies 8 participants last post by  sparky1016 
#1 ·
About two years ago, at 125,000, I replaced the major cooling systems components: Accessory Belt Tensioner Assembly, Idler Pulley, Upper and Lower Radiator Hoses, Thermostat, Water Pump, Coolant, and Fan Clutch. After the job, the cooling systems was fine. No leaks, good temperature.

I only put about 5,000 per year on the car and now have 135,000 on the clock. This summer, on hot days, the temperature gauge creeps up to past 90c and sometimes approaches 100c degrees.

I've done my share of reading on this topic and realized that the Auxiliary Water Pump was not working. I replace the aux pump and the fan clutch too. I was unsure about the fan clutch and replaced it for good measure.

The car continues to run hot even without the air conditioner being used.

In full disclosure, the air conditioner also has an issue. The A/C was blowing only moderately cold air. I brought the car to a local foreign car mechanic (I do not have A/C tools). After evacuating and recharging the system, the mechanic told me the car needed a new compressor, condenser, receiver dryer and expansion value. $2,000. For what it's worth, even after the vac-recharge, the front A/C electric fans were not on. I asked the mechanic about that and he said because the condenser was blocked, the pressure switch was reading insufficient charge. I figure I'll deal with the A/C issue later.

I'd appreciate any feedback and suggestions.

Thank you,

Jay
 

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#2 ·
You seem to disconnect two issues which, in my view, are connected.

You have an A/C problem which you are prepared to put up with for the moment, but the two electric fans in front of the radiator are not just there for the A/C. These fans are intended to provide additional cooling when the engine coolant temperature and ambient air temperature are such that the viscous clutch fan is unable to draw enough air through the radiator to cool your engine coolant adequately.

You do not disclose in your post that you have witnessed the two electric fans operating under any circumstances. The two fans are meant to turn on at 105C and turn off at 94C. Member 43sqd explains it very well here :

Here is the way the cooling fan/s system works.

1. driving without the A/C on, providing everything is in working order, the belt driven fan w/clutch provides enough cooling to keep it at 80°C.

If one or more components are not in working order, the temp. will rise and when it reaches 105° (221°F) the two electric fans will kick in and lower the coolant temp. until it reaches 94°C and the elec. fans will turn off. It will repeat this process until the component problem is resolved.

2. driving with the A/C on, the fans will constantly run until you turn off the A/C. This is why while you have the A/C on you can maintain 90°C, but not 80°C, because the clutch fan is not spinning fast enough.
I suggest you might want to read this whole thread : http://www.benzworld.org/forums/w163-m-class/1847953-trying-pinpoint-cause-ml430-overheating.html
 
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#5 ·
Thank you 43sqd for your reply.

My original replacement fan clutch purchase was a Meyle brand. My most recent purchase (the one that is in the car now) is a Sachs brand.

I used Mercedes Benz labeled anti-freeze. The part number is BQ 1 03 0004 and the color is blue - 50/50 mix with distilled water.

Appreciate the help!
 
#6 ·
mrz, I was out most of the day.

Without the A/C on, does the temp. needle creep up at idle speed or do you have to drive it for the needle to creep up?

If it creeps up at idle, wait for it to do so and place a house fan in front of the grille and see if the temp. drops.
 
#9 ·
The temperature gauge gets close to 100 degrees - but never touches the 100 degree point. That being said, I can not remember the last time those fans went on.

I will try the house fan, but I may not be able to get around to that done until next weekend.

Appreciate the help and suggestions!

Jay
 
#21 · (Edited)
The electric fans never turn on - even with the A/C switch depressed and the compressor engaged. And the temperature gauge is creeping up - even though the ambient temperatures are down from the 90 degree range into the 80 degree range. I'll attach a picture. Fuse F44 is fine, although it is 40amp, not 30amp as indicated in the fuse chart.

Thanks for your help and recommendations. I'd love to get to the bottom of this one.
 

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#11 · (Edited)
Hmmm . . . thought the temp shown is correct operating level. Mine stays at between 80 and 100, just as shown all the time. Closer to 80 when cruising at freeway speed with A/C on, getting close to 100 when climbing up the hill, but never touches 100.

Almost all of my cooling system components are original except periodic coolant(Gerex G-5) flush.
 
#15 ·
Not uncommon but might be a sign something is out of specification?

I have the very same "issue". I have replaced the wrong coolant with G05. I'm now in the process of adding oil to my existing fan clutch (removed; waiting for Amazon to deliver the oil).

I'll report my findings. I'm hoping to stay around 80 all the time. My electric fans work but my temp still goes >80 at idle on a super hot day. I'm hoping the fan clutch gives me the extra air flow I might be missing.

My aux water pump is working correctly as well and I believe my water pump is fine (no leaks; seems like pressure builds up when I pinch the hose after she's hot).

If I still have the problem after addressing the fan clutch, my game plan is to replace the thermostat. If that doesn't address it, perhaps it is "normal".... ??

Steve
ML NOOB
 
#16 ·
Hi 43sqd, sorry about the delayed response. I've been working late.

With the A/C on and the temp gauge between 85 and 100, the electric fans do not come on. The mechanic I spoke to about the A/C system said the condenser was "clogged" and therefore the pressure switch was never getting a proper reading. He said there was a big disparity between the high side and low side readings - even though the A/C system was filled with the proper amount of freon and oil.

As always, I appreciate your feedback.

Thanks and have a great evening,

Jay
 
#20 ·
Im coming from the late 90s rover V8 world. Those engines, and the vehicles they are in (Disco 1&2, P38), are notorious for cooling system issues and sensitivity to even mild "overheating". "Overheating" is in quotes because temps consistently above 212°f are considered to be too high, yet the temp gauge on them does not start to rise from "normal" until you are at about 230°f. A common mod is to swap in a 180°f thermostat which keeps peak temps in the preferred range of 195-205°f, assuming your cooling system is relatively healthy.

The point of this is...

90°c = 194°f and 95°c = 203°f. Peaking at those temps would be totally fine in the 50 year old POS rover v8. I cant imagine modern engines like the M112/113 would find those temps to be a problem.
 
#22 ·
A month has passed and you seem to be focusing on describing the problem over and over rather that doing a bit of obvious diagnostics to establish whether or not the two fans are at fault.

So you say fuse F44 is good. But what about letting the car idle allowing the temperature to creep up to 105 degrees (when the two fans should then switch on) and testing with a volt meter to see if suddenly you get 12 volts at the fuse? Simple test. If you do then this will prove everything upstream of the fuse is good (i.e. all of the A/C control system) and point to the fault being downstream of the fuse.

So if you do get 12 volts at the fuse the next component to test is relay K26. Remove relay K26 and swap it with another identical relay and see if the fans come on (above 105 degrees).

If the fans still don't come on then fish around behind the left headlight for the electrical connector in the wiring harness which runs to the fans. Separate the connector and test for 12 volts on either of the two green wires (labelled C and D on the connector). If you get 12 volts here then it would seem to me that your fans are probably faulty.

You could then check with an ohmeter to see what resistance you get at the connector across the fan motors - test across wires A (tan) and C (yellow) which is the right fan, and B (tan) and D (yellow) which is the left fan. You should get some resistance reading in both tests - not sure what - but if you get infinite resistance in both tests then both fan motors may be burnt out.
 
#23 ·
Hi RJV,

I appreciate your feedback. This information is very useful. Based on your advice, here is the testing that I performed and the results I received.

I let the car idle with the A/C on for quite a while, but the temp gauge never went over 100 degrees. The temp never, ever goes above 100 that I have seen.

I removed relay K26. I was getting +12V to slot 30. I put a jumper across slot 30 and slot 87 and both electric A/C fans went on properly. So I know the fans are working when voltage is applied directly. For what it's worth, I was also getting +12V to slot 86 of relay K26.

I swapped relay K26 with relay K21, and the fans did not come on by themselves.

Please let me know your thoughts and thank you for your help.

Jay
 
#25 ·
Thanks for your follow up, RJV. Perhaps the coolant temp switch is not triggering the AAM because the coolant is not reaching 105 degrees, and the AC pressure switch is not triggering the AAM because of the AC problem?

I can check the relay next chance I get.

FYI, all other functions of the AAM work fine and the e-box fan is working to keep the AAM from overheating.

Thanks again for all of your help!

Jay
 
#26 ·
Perhaps the coolant temp switch is not triggering the AAM because the coolant is not reaching 105 degrees, and the AC pressure switch is not triggering the AAM because of the AC problem?
But if you let your engine idle for long enough and the fans are not running then of course the temperature will reach 105 degrees .... then 115 degrees and then 125 degrees .... if the engine doesn't overheat and seize first !

My point is that you have to test rather than keep guessing. I'm not saying seize your engine. But if there are two theories then you need to eliminate one (or both) or no progress is made.

So in this case, find a way to know what your coolant temperature really is. You say above that the coolant is not reaching 105 degrees - which cannot be correct (at idle) if the fans do not come on. All that you can say is that your temperature gauge does not go higher then 105 degrees - which (at idle) means your temperature gauge is inaccurate or broken, or that you are not being patient and waiting long enough.

If you cannot determine what the actual coolant temperature is, then spend the money and install a new temperature sensor and see what happens. Or go the other way and spend the money and install a new pressure switch.
 
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