HI,
I wonder if someone can help me with the problems I am having with the cooling system.

My car is a 2001 c class W203, I have no heat in the cabin 90% of the time and only 10% of the time I have little heat only if the fan blower setting is halfway.

For the past couple of weeks, I have been getting a check coolant warning coming up on my dash. I fill up coolant almost everyday but the warning sign keeps coming back obviously because I lose coolant.

I have thoroughly checked my vehicle for any visible leaks, there is none.
I did however find that whenever my car reaches normal temperature, the coolant flows out of the expansion tank only when I switch the engine off.

I changed the expansion tank and the cap but no difference.

The car does not overheat.

I also removed & tested the thermostat to see if it opens at the required temperature by boiling it, it seems fine.

Any thoughts please?

Thanks.

 

The fact that you have no heating in the cabin makes me think that the auxilliary cooling pump has failed & probably leaking.

 

Thanks for your reply.

Is that the small pump that only comes on when heating is required right next to the expansion tank?

If so, I checked & it seems fine.

Any other suggestions please?

 

Yes, auxilliary cooling pump is that little pump right in front of the coolant expansion tank,... it has about 3 hoses coming out near the bottom and a wire connector at the top. Since its relatively high in relation to the rest of the cooling system, if the coolant level is low (due to a leak) there may not be enough coolant to get to the dash to heat the cabin.

Do a resynch of your cabin heater-cooling systems - press Recirculation button and FrontDefroster together until you get their blinking lights alternating. The Resynch should stop itself in a few minutes if everything is fine. If not it won't stop by itself.

If coolant is constantly being lost, the coolant must be going somewhere. Are there any bluish (Yellowish in North America) coolant stains in the engine bay?

When car is running, is there thick whitish-bluish smoke out the rear exhaust? If so coolant is leaking into engine via leaking gasket.

Since it's a 2001 model, check your radiator,.... is it a Valeo (Made in France) radiator? Or a Behr? Search! The Valeo radiator has a history of leaking coolant into the transmission via transmission cooler which could cause some serious transmission damage.

 

Thanks for your reply SunnyRay, much appreciated.

I have checked for any leaks near the water pump and all over under the bonnet aswell as near the aux pump, there seems to be no leak whatsoever, except that it pours out or overflows the expansion tank. I noticed that it doesn't happen all the time.

The temp stays at around 95 degrees.

When the sign for low coolant comes up, the coolant is actually low in the tank.

When i switch the engine on in the morning with the bonnet up to monitor coolant level, the coolant goes down by about 2-3 inches in the tank as soon as i start up, and then comes back up again often overflowing after the car is driven for a bit and the temp reaches normal when engine switched off.

The aux pump that has two hoses attached, are they meant to be cold?

I did the sync cycle the light blinking stops itself so that seems fine.

There are no blue or yellow stains or any other stains on the engine except for the marks around the expansion tank only when overflows. Also no smoke out the exhaust to indicate head gasket failure.

In regards to the radiator, i will look into that, transmision seems fine though.

Thanks.

 

How sure are you that the thermostat is fine? If you had it out you should have gone ahead and replaced it instead of putting the old one back in. Granted I don't know how much they are so maybe it made more sense for you $$ wise to put the old one back in.

I know it's a different car but I had the same exact problems with a Jetta last year. Culprit was a bad thermostat. Coolant light would come on while driving and as soon as you turned it off it would start boiling out of the expansion tank.

 

You probably have multiple issues,.... when was the last time the coolant was flushed? Thermostat changed?

Exactly which warning are you getting? "Coolant Visit Workshop" or "Low Coolant Level Visit Workshop"?

Did you mess with that little auxillary coolant pump (in front of the coolant expansion tank)? It almost sounds like the hose are on reverse and pumping coolant away from the cabin. Make sure the wires on top are inserted properly in the right way. Best way to test is to take the auxiliary coolant pump off and place bottom part in bucket of water while giving the pump some power to check that it works properly.

If have or can get an OBD2 Scantool code reading, check for P0128 which means you need a new thermostat.

If your car has old thermostat, it should open at 87C; new redesigned thermostat opens at 90C (I'm referring to M271 engine which may not apply to you). That said, you're reading 95C, which is too hot and points to a thermostat that fails to open properly,... if this is an accurate temperature reading, you need a new thermostat.

The computer monitors engine performance, if temperature reading isn't as expected, it'll throw an visit workshop warning.

How are you reading 95C? Are you using infra-red temperature tool? The coolant temperature display on our pre-facelift 203s only display useless bar graph. What does this useless bar graph say? Sometimes, if the coolant temperature sensor fails, it'll be stuck at 80C.

If I was you, I'd start by changing the thermostat. Search for DIY.

Probably a good idea to also flush the coolant. Should be done every 5 years. Depending on your location, 50/50 mix with MB Coolant (Zerex G-05). Remember to fill it to the fill line of the coolant expansion tank,... that line near the top where the white tank meets the black lid, do not fill it to the very top of the cap.

Does your 2001 C180 have M271 engine? Take your VIN to MB Stealership, and they'll know which part you need.

These are the Canadian Mercedes-Benz Stealership prices when I did mine a few months ago (US prices are usually about a quarter or a third cheaper):
Thermostat:
Mercedes-Benz Part# A271-203-05-75 $60.90 (90C no more 87C old: A271-203-03-75-92)
Thermostat O-ring:
Mercedes-Benz Part#: A271-997-00-45 $2.77 (old: A271-200-00-15)
O-ring:
Mercedes-Benz Part#: 029-997-21-48 $2.41

Coolant Temperature Sensor (Even if yours is still good, this part has been redesigned a number of times and its cheap anyways):
Mercedes-Benz Part#: A000-905-07-00 $21.55 (old: A000-542-51-18 / A000-542-28-18)

Breather Pipe Socket (between Radiator Hose & Breather Pipe) (If this has never been changed, its probably about to break!):
Mercedes-Benz Part# 003-997-06-89 $7.60

Obviously, if you don't have the M271 engine then the above part number would not apply to you, but it'll give you an idea of the part and prices.

You really need to figure out where its leaking coolant. When you start and test the car, the car is level right? Its not like car is on slope with nose pointed down and when you start engine, open (failed) thermostat allow all coolant to radiator and there's not enough coolant to reach the cabin. Kind of sound like you have really high water percentage in coolant since water expands when it heats up.

 

Thanks for your help guys, much appreciated.

jsbaker, I only replaced the thermostat about 2yrs ago, hence why I put it back in after checking. I will probably change it anyway within the next few days. The car seemed fine today after I bled the cooling system.

SunnyRayToronto, The coolant was flushed 2yrs ago when I replaced the thermostat the same time.

The exact warning I am getting is "Check coolant level"

Did I mess with the aux coolant pump? Well I replaced that about the same time as I did the thermostat 2 yrs ago. I was having heating issues initially from then.
I can definately feel the vibration when I put my hands on it and hear the sound on the aux pump when I switch the heating on, I will however take it off & check it in a bucket of water as you suggest.

I did connect an OBD2 scan tool few days ago, I only get a code for my MAF sensor.

The engine temperature reading I am getting is from the useless bar graph on the dash, earlier I was meant to say that MAX is 95 degrees (in traffic really) otherwise it stays at around 85 degrees according to the graph reading on the dash.

I will change the thermostat within the next few days.

My W203 engine is an M111.

When I start the car to test, I make sure its on a flat surface and levelled correct.

I bled the coolant system today and it seemed fine all day, no coolant low sign came up, no coolant loss from the expansion tank or otherwise. However only lukewarm cabin heating.

I heard these cars self bleed the cooling system as I found no bleed valve.
I still bled it my way. With the engine on and rad cap off, I let the car reach normal operating temp, loosened the clip which is holding the hose to the thermostat housing and pried it with a screwdriver, air did come out for sure.

In regards to the parts you suggested above with the part numbers, thanks I really appreciate it. I will consider those.

The two hose on the aux pump, are they meant to be very hot??
Its only warm I would say.

Thanks again.

 

Given that the thermostat has already been changed, you're NOT getting the P0128 code, its NOT complaining about thermostat in the Visit Workshop message and you didn't really get an accurate measure of the coolant temperature,.... you do NOT need a new thermostat.

The usual way to bled the coolant is after a coolant flush, drive around to get engine to operating temperature 87C-90C and turn on cabin heater with fan to ensure coolant flowing into cabin heater. Maybe "massage" the coolant hoses to encourage air flow. Top off coolant in about a week.

What coolant did you use last time? Was it MB Coolant or Zerex G-05? Was it in 50/50 mix? If so it should be good for 5 years or 150,000km.

With low coolant level indicator, you do know that that sensor is connected in series with low windshield washer level sensor, so sometimes a low windshield washer fluid level will show low coolant fluid message. So just make sure windshield fluid are topped off too.

Whats Hot and Warm is relative to different people. That said, the hoses at the auxiliary pump are not too hot since you're feeling the temperature from the outside of the hose.

 

What level are you filling the coolant surge tank to? There has to be air space. If not you will push out coolant due to heat soak on shutdown.

Another thing - on 2001 models you get a low coolant warning when the windshield washer tank is low - so top that up.

M111 engines have a habit of leaking coolant from the rear of the head so check that.

 

The vibration could also be from the engine itself. Best way to test is to take auxiliary pump out, place bottom in bucket of water and hook up power. As I recall water should be going out the side nozzle which hooks to cabin.

"rad cap"??? I don't believe your OEM radiator should have a rad cap. Maybe you meant cap on coolant expansion tank.

 

I have now changed the thermostat and waterpump as I was still having problems.

Its MB coolant I have been using.

I am aware of the sensors being connected to both the windshield washer & coolant, windshield washer tank always topped up and as the low coolant sign only comes on when the coolant level drops, I have ruled out the level sensor issue.

The problem is still there.

Bleeding the cooling system through the thermostat housing hose did improve for a few days, however problem still there.

I did find a leak on the side of the block. I believe it is called the 'freeze plug' or 'casting plug' where its leaking from, only a small leak though.
http://www.automedia.com/Replacing_a...cr20070401fp/1

I am confused as to what to do now.

 

Thanks Glyn.

Please refer to the above post.

I did check the rear of the head which seems fine.

Thanks.

 

I meant the coolant expansion tank cap.

I did take the aux pump out to test in a bucket of water, it ran fine, thanks.

 

I think your Duovalve on the heater circuit is gummed up - common. Needs cleaning or replacement.
You might have more than one issue here.

 

I wasn't aware my vehicle had duo valves.

Correct me if I'm wrong please, where is it located if does have them?

Thanks.

 

Oops, sorry - you are correct. Aux pump & flaps do the job of the duo valves on the W203. Then you have a blockage on the heater circuit or flaps jammed closed if you have no heater.

 

No probs Glyn, I appreciate your help.

My car has started to overheat a bit now.

It goes upto 105 sometimes. Totally confused I am.

Will a blocked heater core cause this problem?

With engine off, ignition on, When I take the blower setting to midway when the heating control is on full, I can hear coolant rushing into the heater core it seems to me, I then take the blower setting to zero and do the same, I can hear the coolant again. It does that atleast 5 or 6 times.

Any diagram available for the heater hoses etc. to maybe indicate which hose is inlet/outlet?

Thanks.

 

Sorry - I was thinking W202 - forgot they simplified the 203.

 

Thanks Glyn, I appreciate your help.

My car has started to overheat a bit now.

It goes upto 105 sometimes.

Will a blocked heater core cause this problem?

After the car has ran for a while, when I switch the engine off but leave the ignition on, I take the fan blower setting to midway with the heating control on full, I can hear coolant rushing into the heater core for about 5-10 seconds, I then take the blower setting to zero and do the same taking it back upto midway, I can hear the coolant again for another 5-10 seconds. It does that atleast 5 or 6 times.

Any thoughts guys?

Thanks.

 

If you don't see any steam.. sorry to say.. head gasket.. you're eating water in some way. Its not leaking or steaming out of anything visible. So that means its being "consumed" in some way.

What I would do before things get worse is take it to an mechanic that specializes in these cars. If you can't just buy a head gasket kit and go to town. It'll put you down for a weekend but its better to deal with this now before you really cause any damage.

 

oh and in case I didn't make this any clearer... DONT drive the car any more till you get this fixed. Metals aka engines don't react well too overheating. If you are lucky to identify the problem and fix it. You'll be able to use the car for much longer. If you happen to overheat it though.. it won't last long. Heat isn't a joke. Take it from a rx7 guy... don't go down that path. It doesn't work out betting that it'll last.

 

This could well be a head gasket failing.

 

Thanks for your input Speed7, much appreciated.

I actually lose coolant through overflow from the expansion tank and a leak from the 'freeze plug' on the block I only recently noticed.

The vehicle started to overheat only after I recently (about a week ago) changed the thermostat & the waterpump, before that it never has overheated at all. After replacing these parts, It only overheats slightly at idle.

I can hear the fan come on at about 95 degrees celcius. It normally stays at 95 most of the time, sometimes drops to about 85 even when the motor has been running for a while. The highest temp it went upto is about 105 degrees only a couple of times few days ago which I assume is overheating otherwise it stays at 95 with the fan on.

Thanks.

 

I checked my heater core for blockage today just briefly, I opened the outlet hose from the heater core and ran the car with the heating on full, very little coolant was coming out the outlet, no pressure or force at all.

Could this cause an issue with coolant not circulating or causing air lock in the cooling system which would result in overheating slightly?

Also bottom radiator hose felt cold, is that normal?

I am preparing for the worst though, head gasket oh no.

Should get the chemical test done soon to determine if it is the head gasket.

Thanks.