Overheat while car is idling (250SL)

[Nivle838]

Would like to know if anyone has solution for car overheating while idling, have fixed the clutch. One mechanic said by adding another fan and try to have a box to concentrate the fan

[JamesL]

Obvious ones would be make sure the fan is running properly - perhaps have it switch on at a lower temperature. Make sure your radiator (and the rest of the cooling system) is working as efficiently as it can (clean cores etc)

IIRC there are some folk who have put on a bigger/more bladed fan and a bigger radiator. However, not a problem in London!
I assume you are running an A/C too

[Tyler S]

The 250sl has the largest radiator of all the 113’s. It is usually not the issue unless it is severely plugged. Check the thermostat and water pump. Another issue could be a blown head gasket.
Try idling the car just off normal idle at about 1000 rpm. Use a piece of folded paper under the throttle stop to achieve this. If it continues to overheat then lean twards the thermostat or air in the system, plugged radiator. If it doesnt overheat, you have a coolant or air flow issue. Having a fan shroud makes a huge difference.
My 250 used to overheat because the small coolant bypass pipe between the water pump housing and the head was plugged solid. This caused air to be trapped in the top of the head.

[mbzse]

I support what Tyler writes. The cooling system as it is designed, from factory, is able to keep engine temperature in ok range. Go for ensuring that components and system is ok. This is before even considering extra fans and other such measures

[Atazman]

I just went through the cooling system on my 250 SL.  Here is a link for you to reference:

https://www.sl113.org/forums/index.php?topic=27865.msg201057#msg201057

As others have suggested, there are several possible causes for overheating.  Unfortunately, I found it very difficult to determine (by testing) which items were faulty.  Being that my system was "old", I changed just about everything, so I don't really know which change solved the problem.  More than likely, each change had somewhat of a positive effect. 

My radiator looked really good from the outside but the core was partially plugged when the radiator shop removed it.  It definitely needed some help.

Please let us know what you do to solve your problem.

[zak]

My 67 250 SL - # 3019 has rock solid engine temps at all times and all conditions, even idling.
So I would take Tyler's wise advise.
Good luck,

jz

[Iconic]

My 67 250 SL - # 3019 has rock solid engine temps at all times and all conditions, even idling.

Maybe your temp gauge is broken???   
Seriously, your cooling system must be in tip top shape.

[Atazman]

Zak....

Just curious; do you have A/C?  Fan shroud?

Thanks!!

[Bonnyboy]

I always do the easy stuff first so...If you don't know for sure that your radiator is working at 100% take it to a rad shop and let them let you if it is at peak performance.  What I thought was a perfectly good radiator in another car turned out to be marginal at best with a whole corner gummed up.   The rad guys cleaned it up and all is well.   

Also - how old is your coolant and do you have the correct type.  May be time for a complete rad/engine flush (my coolant had "jelly like" clumps until I cleaned it all out )  It took 2 flushes for my coolant to run clear.   Test the antifreeze if its history is not known. 

[Tyler S]

The 250’s dont usually have the overheating issues that the 280’s face. Assuming everything is functioning properly.
I have seen water pump impellers widdled down enough to cause a flow issue at idle. You will never find it unless you remove the pump.

[Mike Hughes]

I have seen water pump impellers eroded to barely a stub on the end of the shaft, a condition hastened by infrequent coolant changes.  So the only circulation of coolant is by thermosiphon (convection).  Before WWI and even up until the early '30s engines often circulated coolant by this principle, aided in part by a significant area of the radiator located above the highest point of the water jackets in the engine.  Modern high compression, high performance engines with low set radiators rely on a properly functioning water pump.

[Rolf-Dieter ✝︎]

In my case it was the Fan Clutch (small fan inside the cooling fan) that was the culprit. Once we replaced it all was well. However, mine is a 280SL not a 250SL

Dieter

[peterm]

Steuben day parade up fifth avenue yesterday.  By 80th street I had the heat on and was idling with higher rpm in neutral to keep it down below red.  By 86th street it was well over 250. An hour and a half of crawling behind the Austrian boys float not so good.  I already have on my 280 a New radiator / fan, fan clutch water pump thermostat etc.  I pulled off at the end and let it cool. The gauge was buried in the hot zone but I don’t think I cooked them cylinder head -whew.   Any suggestions if I go again next year?

[ja17]

Make sure your ignition timing is right, can cause overheating and shifting problems on an automatic, if is off.

[WRe]

Hi,
even if you replace all (outside) cooling components and your adjustments are alright there a 2 things left:
- limescale and mud inside your engine that retards coolant flow* and
- (my personal opinion) a faulty designed fan/visco clutch that doesn't provide enough power during low speed (traffic jam, city traffic, aircondition, ...); see threads "overheating, cooling, electric fan".
...WRe

*  https://www.sl113.org/forums/index.php?topic=27735.msg199515#msg199515

[Garry]

Totally agree with WRe.  Unless you do a full chemical flush of your whole cooling system, then just changing out the external components to the engine are just not enough.  Once I had done that in my old 280sl my temperature never went above 180 even in extreem Australian heat of 40c days.


Garry

[zak]

Sorry Don, I just saw this.
No, I have no AC but I have the fan shroud.
My 250 SL is a euro, 4 spd and an early " late " model.

jz