1970 280SL engine temperature

[Mechudo62]

 I have replaced every component of the cooling sytem and installed the auxiliary kit for cylinder head, but the engine tends to overheat in heavy city traffic. I have performed tests with engine running and transmission lever in (4) D with hand brake engaged replicating a traffic jam in my garage, and the needle goes up to the last white square on the gauge which I believe is normal. However, in real world conditions in city traffic, the needle goes past this white square but not to the red square, making me nervous about a possible overheating engine. When this happens, I turn on the heating system to force coolant through the heating panel underneath the dash that acts as a 2nd radiator in the system, and this seems to help control the engine temp. Is there a way to keep the temperature in the low range? What modifications, if any, are effective to control the temperature on these cars? Maybe my gauge reads a few degrees higher than actual engine temp? What is the correct range of movement of needle in gauge?

[kampala]

Mechudo,

The temp was rising like you describe on my '71 280.   The radiator shop asked me to drive and check one additional thing.   They asked I drive it on the highway at speed and advise if temp is staying low or rising.   Mine was not staying low on highway and rising slightly.   This was a clear indication for them that my issue was the Rad itself as even airflow at highway speed was not enough to keep it cool.  This ruled out fan and such. You can see the flow when we pulled it and tested it on the photo.   Once we achieved full-flow, the temp gauge does go to the first white dot as you describe on very hot days in traffic, but holds at that point. 

The '70 and '71 USA models do have a sensor on the thermostat housing that triggers the distributor to advance a bit to raise rpm at idle to help cool.  I have disabled this during my switchover to the 123 ignition and still not had any issues. 

You need to isolate if it's an airflow issue or a rad issue.  That's why they had me drive it at speed.   As you will  find, many folks here have added electric fans etc.   I've not needed to do that. 

[Mechudo62]

Thanks for your reply Kampala,
I have replaced the radiator with an original Behr,  along with thermostat, water pump, fan clutch, hoses and belts from the MB Classic Center. I kept the original ignition system with the sensor for increasing RPMs if temperature rises to the top white sqaure (212 degrees F); at which point the engine seems to vibrate more beacause the fan clutch fully engages, but RPMs stay around 750. If traffic is moving somewhat, even slowly, the temperature holds here. If traffic is almost not moving at all, then the needle may fully point slightly above the top white square. I don't dare turn on the air conditioning at all unless on the open road.  In highway driving the car performs beautifully, it is correctly tuned with excellent power and torque and the needle stays between the two white squares. It may go near the top white square in prolonged uphill mountain driving, but returns to the center on level terrain or near the bottom white square (180 degrees F) in downhill driving. Should I check anything else? Am I missing something, or is this the way the later 280 engines perform, running a bit hotter ?

[alpina]

Your temp gauge would seem to read the same as mine. In normal driving the needle sits in the
Midway between the white square dots, rising a little as yours with prolonged uphill driving.

Looking at the history files of my car, I noticed the gauge was changed in 2007. The gauge has been
Out a number of times since then for engine work and painting.

 If I look very closely at the gauge the needle does not come to rest on its stop. It always sits slightly above the stop
 (even on the coldest of days).

I have come to the conclusion that my temp gauge reads high. When tested with a IR temp gun I get readings
Of 72C – 79C at the thermostat casing, top of the radiator and temp gauge pick up point.
The dash gauge needle would read midway between the two white squares.

I would be very interested in anyone who could test their engine temps with an IR Gun and where the
Gauge needle sits.

http://www.sl113.org/forums/index.php?topic=23973.msg171850#msg171850

[Benz Dr.]

I've found that late 280SL's have a tendency to run hot because of the ignition retard system. By the time the switch on the thermostat housing closes at 100C, it's already too hot to cool off in stop and go conditions. Try a bottle of water wetter - it can't hurt and I've had good results with it. You can also try moving your rad closer to the fan so it will draw more air through your rad. You do have the fan shroud in there, right?

[TJMart]

My  1970 280SL ran hot all the time. I found out that Mercedes came out with a bypass solution to fix the problem. My mechanic installed the bypass and the temp gauge now is at 180 and does not deviate even with the a/c on.

[Mechudo62]

In addition to the ignition retard system, I've also heard these '70-'71 models 280SLs run hot because the engine size increase from 230 to 280 reducing coolant space within the block. My car has its fan on the stock location with its shroud in place. I have installed the coolant bypass and has helped little lowering engine temperature, if at all.

Its odd Mercedes´engineering allowed this design compromise with potential for easy overheating to reach production. I will try a bottle of Water Wetter and see what happens...

Does anyone know if Mercedes offered cooling system components for hotter climate conditions, other than the above mentioned cylinder head coolant bypass kit?

[Benz Dr.]

It goes back further than that and right back to the 220SE in 1959. The external block dimensions are actually the same while the cylinders were spaced closer together and 2.8 liter was as large as they could take it. So, in essence, a 280SL is a highly modified 220SE. All that cylinder space leaves little room for coolant so it's no surprise that they run hot. There used to be a tropical fan option for earlier cars; not sure if that was available for Pagodas.  Make sure that your oil level is full as oil acts as a coolant and if you're low it will add to overheating. 

 

[Mechudo62]

Thanks Dr., thats why they added the oil cooler but probably stretched engine displacement too far within the same block. I will add the Water Wetter, change engine oil and ask the Classic Center guys at Irvine for a tropical fan option or cooling system components. I will let you know the results.

[alpina]

Will anyone be able to take IR temp gun readings at the cylinder head, top radiator
Hose etc and compare these with their dash temp gauge.  Someone... anyone...

[langa01]

My two cents on engine temp and a question to the group.:
About a year ago (but only 400 miles or so) I had the engine in my 1970 280 SL rebuilt. The job included new rings, crank bearings, new timing gears, new chain etc. a comprehensive rebuild done by a specialist. Before this, the engine ran at a steady 180F (80C)  no matter the conditions however after the rebuild it now runs considerably hotter, particularly when the engine is worked a tad harder (think slight climb) it reaches the mark above the 180f marking on the instrument. At the beginning I thought it could be due to higher friction on a new engine etc but I am now convinced it is something else. BTW as part of the work done, a new set of radiators (coolant and oil) were installed. Judging by the way the temp behaved I started to suspect the thermostat (a new item). Today I enquired in my local MB dealership (Madrid, Spain) about a new item and I was told that the stat is rated at 87C which might explain the extra temperature in the engine, past the previously steady 80C. I went back to my stock of old but yet serviceable spares and dug out the previous stat. I noticed It had been modified with a piece of plastic tie sitting on the stem so that the thermostat can never be completely closed!! mystery solved apparently. Now the question is: do you know if there is another MB stat that may open earlier than 87C and can be fitted without having to resort to the crude measures found in my old stat? The car has its original shroud surrounding the fan, the viscous coupling is OK etc so it seems to me the stat is the critical component here and would like for the engine to run a touch cooler.....

[Jonny B]

There is a lower temperature thermostat - 79C available. That is what I have installed in my 280 SL.

[Iconic]

Mechudo62,
I agree with Dr. Benz about the Water Wetter.
I also want to throw in the idea of rebuilding your new radiator from 2 rows to three rows.
The tubes are smaller, but the net result is more coolant flow.
I know this is not "stock", but my '70 only started heating up when very hot outside in stop and go traffic, then, with the re-built three core radiator, I rarely heat up.
Mark

[Benz Dr.]

I drill a small 1/8'' hole in the thermostat which will not effect engine temperature but will release any trapped air behind the thermostat. If your engine overheats very quickly from cold you will have trapped air in the block - this small hole will prevent that from happening.
 Removing air from your coolant is very important and that's what water wetter does. It also removes some of the surface tension in the coolant and makes the coolant bite into the metal surfaces of the block and rad. I've seen this stuff pull operating temps down a couple degrees which can often be enough to keep everything running.

[Rick]

The W113 does have a hot running tendency.  My '71 280SL did not run hot with the original engine.  The car had sat for quite a few years and I recently installed a quality rebuilt short block engine from Metrix.  I also installed a 3-row high efficiency radiator built for it at the time of the engine exchange.  The head was original, it had been rebuilt at one time and visually appeared clean.  The car has AC which I haven’t charged up yet, the condenser core is mounted in front of the radiator.

After the work, it would run hot, particularly at slow engine idle speed and this was in 90 degree weather. The temp gauge would move up to the red mark, especially if it idled for long. ---- Interesting enough, it would cool down slowly at highway speeds. But- If I put in the clutch at highway speeds- thus returning the engine to idle, but with the car still going fast with resulting lots of air going through the radiator, the temp gauge would show it slowly heating up while I was coasting and still at a high road speed.


I did the following -

1) New water pump (the long pump)-  The old short pump has some corrosion showing on the outer 1/4" of all the impeller blades. (see attached picture) The short pump was a pain with the AC and that awful spacer under the pulley.  The long pump is a whole lot better.

2) New fan clutch.  The new Meyle clutch showed some silicone leakage- - It didn’t seem to engage properly, but this should not be an issue at high road speed. I replaced it with a new Febi fan clutch.

3) New MBZ thermostat-  79 degrees-  it has the brass bypass wiggle pin built into it from the factory.

4) Citric acid flush- per Mercedes Service Bulletin . I pre-rinsed with "Shout" detergent. I ran the engine until warm and flushed out the Shout. I put in the citric acid solution and ran again till warm.  I let the citric acid remain in the engine overnight and then thoroughly flushed it out

4) Cool Kit-- this bypasses some coolant from the rear thermo-time switch hole in the head and routes it to the lower radiator hose.

5)  MBZ Coolant--I installed a 50% mixture of MBZ coolant W0133-1635303

After the work, I took it out in California Central Valley heat, when it was 109 degrees outside, I ran slow, fast, and at idle for an extended period and the temp held within a 3 degree range of the 80 degree mark on the gauge.

I can’t say what the issue was exactly, or if it was multiple issues, but something I did fixed it.

[Mechudo62]

Thanks for the advise guys, I haven't tried the water wetter yet, since I was restoring my interior. I will also try all your additional  fixes such as 79 degree theromstat with a small hole and let you know results.
 

[dakman29]

For those with continuing overheating issues, there is a guy who has found the solution.  Check with Scott Melnick at Automotive Engineering/Classic Mercedes Benz in Calabasas, CA.  (818) 222-1800  Scott has done a great deal of work on my 68 280sl, and while I understand that the overheating issue was more prevalent after the 69 model year, Scott can eliminate the problem throughout the 113 series.  I can't share any more information than this but I can vouch for the quality of Scott's work and the depth of his knowledge.  If you've tried everything and your car still runs hot, give Scott a call.