ML270 Overheating

[Neo7]

Hi Gents,

My ML270 has always run quite cool but these past couple of months I've notice the temp 10degC higher than usual.

Yesterday I towed my boat and the engine overheated (120+degC). Coolant spat out of the expansion tank cap and the top hose was under a lot of pressure. Got home in a tow truck and drove it around my property for 10 mins.... It didn't overheat but ran much hotter than it should have.
This morning I started up from cold (refilled with water for now) and left her idling. The top hose became hot and under pressure within 2 or 3 minutes.... I'm assuming that's carries the flow of coolant into (supplies) the thermostat? ... So I think I have a stuck thermostat issue?

Can you please give me your thoughts on this?

 

[Neo7]

Oh and another point ... the fan did not run for most of the overheating and when it did run it didn't seem to be going that fast??

 

[MrGreedy]

Hi there an welcome. No doubt it's hot there down under at this time of the year, but nonetheless, the overheating you are experiencing doesn't sound right.

A couple of things that might help:

- Firstly, it sounds fundamentally like the thermostat is not working as it should. If the thermostat is working and you are driving about (good air flow) then the fan shouldn't need to come on. I would consider replacing the thermostat.

- Secondly, if the fan isn't running on full blast at the temperatures you have mentioned, that sounds like a possible second and compounding fault. I personally would use a good quality fault code and data scanner to look for stored fault codes, and to look and temperatures reported both when cold and after starting and running the car. Specifically of course coolant and oil temperatures. If the temperature sensor that controls the fan (which might be entirely different from the information used to provide the dashboard temperature display) isn't working correctly, I would expect to see some weird temperature readings when looking at the data. E.g. reporting 5 degrees when the vehicle is cold despite it being 30 degrees outside, or significant discrepancy in different oil and water temperature readouts when all up to temp. This might help you pinpoint a dodgy sensor. The fault code/data readers we would typically recommend over hear are either iCarsoft (home use) or STAR for a proper Mercedes interrogation. But other high quality scanners might give you the information you need e.g. Autel Maxisys.

- Thirdly, if the first two don't reveal anything, there have been issues with people on here (and a mate of mine in the past) who have suffered over heating problems and it took ages to find out that it was the radiator that was shot. It wasn't leaking, but either (i) the radiator was externally filthy and full of dust and muck and needed air and pressure washer blasting clean, or (ii) internal corrosion or clogging meant that coolant just wasn't able to effectively flow through the radiator. Cleaning the rad internally is not an option. Depending on where you are, you get some dusty roads out there, so an external clean would at least be very cheap! I'm also assuming that the water pump isn't on the verge of giving up.

- Finally, if you are trying to find what thermostat to use (or whatever spare part) and you can't physically get to the part number to see it, you can use a website like 7zap, and type in you VIN number, and navigate through the diagrams to find the one with your thermostat on. By doing this after entering you VIN number, the results should be specific to your vehicle.

Good luck

 

[Neo7]

Thanks MrGreedy for a great response.

Could you please confirm my understanding of the direction of water flow from the Radiator to the Thermostat via the top hose? ... And also my assumption that if the top hose is under excessive pressure it's unlikely a blockage is in the radiator?

I have a Snap-on diagnostic box. I checked for error codes only last week and there were none for the Fan or anything that could be effecting the Fan ... But I will check again just to be sure.

Thanks for the link but regrettably 7zap does not like or know my VIN

All the best.

 

[MrGreedy]

In order:

- I'm afraid I don't know what the direction of water flow is in the top hose.
- I can't imagine that the water pump is powerful enough to cause a hose to be under excessive pressure. It's a centrifugal pump sat in a 'bowl' of fluid, rather than a high-pressure inline pump with one-way valve installed; think quickly stirring water in a bowl rather than forcefully blowing water through a tube. If there is excessive pressure, this will be down to either too much heat (if the engine is hot), or if it happens when the engine is still cold, it might point towards head gasket. Do you have white 'mayonaise' under the oil cap when the engine has been cool for a day or two, or can you smell fuel in the water system when you take the cap off? When the engine is cold, release the pressure from the coolant expansion cap and refit. Regularly feel/squeeze the water hose straight after startup from cold and it should not be under much pressure at all until the system starts to get warm/hot.
- Snap-on diagnosics would probably be good enough. If there an no fault codes readily available with the snap on code reader, you need to look at the temperature sensor outputs from cold, and when the car is heating to check that the values being displayed make sense. If it's a decent snap on reader you should be able to access this I think?
- I've just tried, and your right, 7zap doesn't like Australian Mercedes VIN numbers. For a replacement thermostat, it looks like the best option is a Merc dealer. Anyway, a lot of people find that fitting aftermarket thermostats on Mercs either don't quite fit, or cause other problems (e.g. temperature set point for opening incorrect etc etc).

 

[Neo7]

Thankfully there is no 'mayonnaise' under the oil cap.

I emptied the coolant yesterday evening and removed the Thermostat (Avoiding snapping the hardened fuel lines was the hardest part). I also ordered a new Thermostat yesterday. But it's an old car so I couldn't bring myself to spend $350! So I had to settle on a $104 "Mahle Behr".... But I have since noticed that the Mercedes logo'd part that I removed has "Behr Mahle" on it

The short rubber pipe is in good condition but I would still consider replacing it if I could get it for a reasonable price. The only way I could do that is to order it from the UK because last time I went to Mercedes they charged me $52 for a regular O-ring .... that everyone at the time told me was a special O-ring.

Anyway thanks again for your help.

 

[Smiley]

If you have the old thermostat off the car then you can test it in a pan of boiling water before buying a new one. I would expect the thermostat to be closed anyway in the first 2 or 3 minutes of running from cold - so it may be something else causing the pressure in the top hose eg head gasket.

 

[ernie]

You mention that the car is 'old'...Some models have water pumps with plastic impellers which eventually crumble to the point where they are unable to circulate the water - I found that out the hard way after a garage tried a few of the things mentioned above and eventually I fitted a new water pump. If none of the above suggestions help, it might be worth removing the water pump to check its impeller as I'm not sure if a WP-specific code would come up using a code reader.

Ernie

 

[zipdip]

As posted boil that thermostat up and see if it opens if it does then again as posted you will have at look at the water pump.

 

[Neo7]

You mention that the car is 'old'...Some models have water pumps with plastic impellers which eventually crumble to the point where they are unable to circulate the water - I found that out the hard way after a garage tried a few of the things mentioned above and eventually I fitted a new water pump. If none of the above suggestions help, it might be worth removing the water pump to check its impeller as I'm not sure if a WP-specific code would come up using a code reader.

Ernie

Great tip .... will be my next job if the Thermostat doesn't fix things up.

 

[Neo7]

Ok I think this is going from bad to unbelievably worse

I fitted the new Thermostat this morning ... tricky but I got it done without any fuel line breakages.
Filled her up with Rad-flush and 10 litres of Demineralised water while she was warming up. The Engine is still running hotter than usual but not overheating (without towing a boat) and hovering between 80 and 90 deg (traditionally stable at 70 to 75deg). The top hose is still under a good deal of pressure. So I took her for a test drive and all hell broke loose....
Oil level warning light came up and the Left side (passenger side or not Tubro side) of the engine is now splattered with oil.... And clack, clack, clack! (in tune with engine rpm) is coming from the top of the engine now too.
But I can't see whats burst (or cracked ) so tomorrow I'll take the plastic wheelarch cover off to get a much better look at it.

I guess once an engine has overheated all kinds of stuff starts to go wrong .... Your experiences, thoughts and suspicions guys would be greatly appreciated.

All the best.

 

[MrGreedy]

Modern engines (I'm including yours) typically run with a thermostat set at 88-90 degrees. 70-something is way too low.

If everything is working normally, under steady/easy driving the temp should be rock solid. Does the temp stay solid of does it fluctuate with the new stat? What is the Merc part number for your thermostat and do you know what its set point is?


I put loads of pointers and things to try in my earlier response but you haven't said the outcome of those investigations/tests. E.g.
- pressure increase on top hose from cold when engine is running. Does it only get pressurised when hot, or does it build up pressure when cold.
- can you smell fuel I you smell the expansion/water tank?
- do you have any diagnostic code reader to look at live engine and coolant temp data to see if a sensor is off?
- Have you tried vacuuming and cleaning/washing the radiator? What condition is the radiator in if you inspect it?
- How hot is it there at the moment when you are having the heating issues?

If all of this seems okay, it could be pointing to water pump, but there are some inexpensive or free tests there that need to be done.


Regarding the clack clack noise, I would start another thread to keep it more focused and point a link in both the threads for the forum readers to easily navigate between the two. First job has to be an oil change if it can be done very cheaply.

 

[Neo7]

Temperature is not stable.

- pressure increase on top hose only gets pressurised when it'shot
- No smell of fuel in the expansion tank or the coolant that came out
- I have a diagnostic code reader but I have neglected to check the codes
- Radiators is all perfectly clean
- Today got up to 23deg

The engine oil has just about all leaked out of the engine (not sure if I made that clear) ... so no need for an oil change yet

 

[MrGreedy]

What is the Merc part number for your thermostat and do you know what its set point is?

 

[MrGreedy]

I would also work on the assumption with the overheating bit, that if it's a perfectly pleasant 23 degrees and you can't maintain a steady temperature, that it's most likely to be either thermostat (replaced), water pump or radiator.

There was a relatively recent thread on here, that suggested viscous coupling on the fan, or an old choked radiator.

Overheating - Stumped | Engine

Being summer here in England, the old Merc is grumpy. For some reason even though I have addressed all the regular overheating issues, I can not get it to sit at the usual 85. It usually goes up to the 90 line mark then above and sits there and after a while, maybe 20 minutes of driving then...

forums.mbclub.co.uk

Do you know if the water pump on your car is direct driven off cam or serpentine/aux belt, or powered some other way?

 

[Trunkz]

Have you checked to see if you have an airlock somewhere in the system? Before all this oil mess happened, when the car was warmed up did you try and stick the heater on full blast and see if the outcoming air from the air vents was indeed hot?

 

[Neo7]

Ok update...
The water pump is driven of the serpentine belt.
There are no airlocks... I spent a lot of time bleeding the cooling system.... Heater is and was working Ok.

The oil leak tuned out to be the O-ring on the Oil filter cap had popped out on one side.... This caused about 5 litres of oil to leak out and the Clack, Clack, Clacking is most likely because the valve guides are damaged now as the noise is definitely coming from the Cams. Before I purchased my ML the injectors had leaked and the previous owner replaced all 5 but the wiring to all the injectors is badly cooked and extremely brittle, so the chances of getting the Cam Cover off without breaking the loom wiring is quite slim.

My ML is also due for it's annual registration and insurance which is a lot of money to pay for a car that not's running. So after 5 years of almost continuous "fun!" I've decided on this occasion to "throw in the towel" and today I went and bought another SUV/Tow Truck.
I had a long look at my browser bookmarks. Pretty much every folder has been a substantial repair project in the last 5 years. Don't get me wrong I have learnt so much from the ML and fixing things is something I always love doing but the volume of issues on this car is more recently stopping me living a normal life ... I'm not actually scrapping the ML and I will attempt to repair the Lifters and Overheating issues sometime in the future.

All the best.

 

[MrGreedy]

Thanks for the update.
I do repairs on my cars that are easy and accessible without having to get under it, but my previous car (Vauxhall/Opel/Holden Insignia) was basically the same. Every 2 or 3 weeks it seems like I was crawling around on the floor or bent over the engine bay or researching in the evenings the new issue. It's quite enjoyable to do a couple of things a year, but when it constantly needs attention it becomes a burden like you say.

 

[Neo7]

Maybe I should change the title of this thread to "I've been overheating"?