SL55 overheating

[zedmeister]

Noticed my car running a little hotter over the last month or so. It used to warm up to just over 80C and then it started running at 90C. Then it started creeping up but the other day, I had the red dash warning about coolant temp and when I looked it was as 120C. Had to park up for 1.5 hours before completing the last 10 mins to get home.

So I ran it up to temp on my drive. No fan. Temp creeped up to about 95. Fan does not go on even with a/c on. Revved the car up but is there a limiter as it would not go over 4000 revs on the drive. Could not get temp over 95 but some steam came up from behind the expansion bottle so I shut her at that point! But def no fan.

I presume that this could be for a number of reasons: fuse, fan, fan ecu, temp sender. SAM unit. Are there any more?

Does anyone have a logical order for attack? Also a list of locations for where these things are and any advice? I presume as the a/c did not switch the fan on that it is unlikely to be the temp sender?

I have checked the 5 amp fuse in the passenger engine compartment fuse box (F49) and this is okay but I thought that fan fuses are usually high amp fuses like 50A or larger? I seem to remember that C Classes have a pre fuse 125A that causes problems with the fan?

If someone has a list of things to check and where I'd appreciate it. My little bluetooth dongle did not find any codes on the car but thats hardly a proper diagnostic tool!

Thanks!

 

[John Laidlaw]

Sounds like the thermostat sticking closed. I think in the 55 it’s under the supercharger? Someone will confirm
But as usual before blasting ahead and changing parts best to get the Star diagnostic done then you’ll know for sure

 

[zedmeister]

Sounds like the thermostat sticking closed. I think in the 55 it’s under the supercharger? Someone will confirm
But as usual before blasting ahead and changing parts best to get the Star diagnostic done then you’ll know for sure

Forgot to mention that the top hose was hot so I presume that the thermostat is okay. Would the thermostat cause the fan not to run?

 

[John Laidlaw]

No - good point that would normally be a cooling fan relay

 

[LostKiwi]

You may have either a failed fan, fan controller of fuse.
Using Star you are able to test each component to pinpoint the exact problem.
You can probably test the fan by applying 12v across the connector pins.

 

[ianplymouth]

My fan motor went last year, to over come the high temp i put the interior fan on full and turned the dials to full heat and opened the windows, kept the engine temp down enough to get home.

 

[zedmeister]

You may have either a failed fan, fan controller of fuse.
Using Star you are able to test each component to pinpoint the exact problem.
You can probably test the fan by applying 12v across the connector pins.

Do you know what fuses to check? I thought the fan had 4 wires so not that easy to apply 12v across it. Are there any cheaper diagnostic tools that I can buy? Don't want to drive to my favourite indie who is 40 mins away with an overheating car. I had heard that there is a really good cheap diagnostic but can't remember which one.

 

[zedmeister]

My fan motor went last year, to over come the high temp i put the interior fan on full and turned the dials to full heat and opened the windows, kept the engine temp down enough to get home.

That sounds like a really interesting technique! I presume the heater matrix uses some of the heat and helps that way?

 

[John Laidlaw]

That sounds like a really interesting technique! I presume the heater matrix uses some of the heat and helps that way?

Quite well known, had to adopt that myself 18 months ago when my SL tried to give me its final insult as I was driving it 260 miles to trade!
I use icarsoft MBII diagnostic tool which is good enough for most things it’s been superceded by the MB V2.0 , uk agent is https://www.ukpartsdirect.com/

 

[L John]

As John Laidlaw says, it's a trick that was often used in the old days when the cars just had a small fan driven by a belt, before viscous fans.
In traffic jams they always overheated because at tick over the fan was slow and inadequate.

Some, if not all, modern Mercedes have the option of running the heater even with the engine stopped (by circulating the water without the engine running) so if you need to stop again, you may be able to use the heater without the engine running so you don't have to wait so long for it to cool down.

 

[zedmeister]

As John Laidlaw says, it's a trick that was often used in the old days when the cars just had a small fan driven by a belt, before viscous fans.
In traffic jams they always overheated because at tick over the fan was slow and inadequate.

Some, if not all, modern Mercedes have the option of running the heater even with the engine stopped (by circulating the water without the engine running) so if you need to stop again, you may be able to use the heater without the engine running so you don't have to wait so long for it to cool down.

I have used that button many a time and sadly miss it from my new e class!

 

[zedmeister]

Quite well known, had to adopt that myself 18 months ago when my SL tried to give me its final insult as I was driving it 260 miles to trade!
I use icarsoft MBII diagnostic tool which is good enough for most things it’s been superceded by the MB V2.0 , uk agent is https://www.ukpartsdirect.com/

Yes, it was mb ii I was thinking about. I could not see the mb v2.0 on their site so I'll call them tomorrow. Do you know if these work with things like SAM or parktronic, etc? Hopefully this would be good for my w208 2002 as well so I think I'll get one if it can pin point the fan problem.

 

[John Laidlaw]

Yes, it was mb ii I was thinking about. I could not see the mb v2.0 on their site so I'll call them tomorrow. Do you know if these work with things like SAM or parktronic, etc? Hopefully this would be good for my w208 2002 as well so I think I'll get one if it can pin point the fan problem.

Parktronic yes Sam I’ve never tried but I’ve seen it in scan through- never so far had to clear a code from that...

 

[zedmeister]

Okay, so I got the new icarsoft MB v2.0 today and gave it a quick go. I could not find any faults except for a/c. I presume that since the engine is demanding fan but it is still not running that it's a faulty fan or fuse? What are the fuses to check?

 

[LostKiwi]

It could be either fan controller or fan.
Its impossible to say which one it will be.

 

[zedmeister]

It could be either fan controller or fan.
Its impossible to say which one it will be.

Is the fan controller available separately? Are there any fuses like the 125A pre fuse on the c class?

 

[zedmeister]

Also, do you know if you can actuate the fan with the icarsoft unit like you can with star?

 

[LostKiwi]

In answer to the first question no idea. In answer to the second one I don't believe so.

 

[John Laidlaw]

Second one is a no sorry