Engine overheating in traffic

[Jimb1231]

My 1970 280SL runs hot while sitting in traffic.  I intend to install the cooling system improvement kit, am considering having the radiator re-cored for a 3 row unit, and will replace the 6-blade fan with a 9-blade fan (if it fits OK), possibly replace the water pump, and install 79 C thermostat.  I haven't researched the availability of shops in my locale who can modify the radiator to a 3 row unit but have seen some posts from others who have done that.  Question is, how difficult was it to find a shop to modify the radiator?  And, did it improve or lower the operating temps?   I'm in Northern Virginia and temps are running in high 80s to high 90s.  I'm hesitant to drive the car locally in traffic till I get this resolved.

Another issue is the engine misfires at higher RPMs when hot making me think it's running too lean when hot.  When first operating, it runs smoothly, even at high RPMs when upshifting or at cruise speed.  I have the Pertronix sold state distributor and have had the car on a DYNO a couple of times for making adjustments to the injection pump system.  Can't seem to find a happy place where everything is satisfied.  I figured that may be overheating situation is also affecting fuel mixture that may be causing the intermittent misfiring at high RPMs when hot.

Thanks for any feedback or comments.

[Rolf-Dieter ✝︎]

Hi Jim,

My major issue was the fan clutch (about 8 inch in diameter and lives in the center of the main fan). The fan clutch was not working and once replaced all was well. I would if I was you first check if your fan clutch is not working (For an image see part 210-150 in attachement).

[rwmastel]

Jim,
Hi.  A wise man (probably JA17) once told me that an engine that is not in tune and running right can cause a bunch of other related problems.  One being overheating.  I'd get the engine running properly, hot or cold - fast or slow, and see if the high running temp clears itself up.  Using a dyno is one way to determine the tune of your engine.  Others are reading the spark plugs, using an exhaust gas analyzer, or having an expert take a look.  Is CTaylor from Falls Church near you?

Hope it works out quick.  It will be a couple months before we get many cool days.

[Benz Dr.]

We had a car in this spring with similar problems. It was also a late 280SL and we found that all of the ignition system quit working and the vacuum switch over system was unhooked. It was also over heating but had been running fine for many years until the rad was recored. The rad checked out fine so we removed the thermostat which was a 79C and drilled a small hole in it. That cured the over heating problem probably due to trapped air in the system. I was also going to add water wetter but found we didn't need it.  As a last resort we would have installed the the by pass system available through Bud's.

 Fixing the ignition system brought the power back and it was a decent car to drive after that. I would put a timing light on your engine and see if you get a 20 degree advance all at one time around 2,200 RPM. If you don't get any advance the vacuum system probably isn't working. Most common causes are missing or broken vacuum lines, broken vacuum cell on the distributor, or a dead speed relay.

[ctaylor738]

You're not too far from Springfield Radiator - Arlington Armature in Lorton.  Also, I know of at least one Pagoda that got a triple core radiator from SL-Tech.

BTW, how "hot" is your car getting on the gauge?  In heavy traffic on a really hot day, my 1970 will get up to the white mark between 180 and 250 which I have come to accept as normal.  I have a new-ish regular radiator and fan.

I doubt that running hot is the cause of your high-rpm miss.  More likely a fuel supply issue, or maybe a tired coil or tired plugs/wires, ignition timing.

Cheers,

[Jimb1231]

Thanks for that info.  I am in Fauquier County - near the Quantico Marine Base.  The shop you mention is not that far from me but at this moment, I'm spending a lot of time in Norfolk/Virginia Beach and have been using a shop there that has a dyno. Fuel mixture was set while on the dyno at 2500 RPM. 

RE: the High RPM stutter/mis-fire, The engine was tuned and adjusted on the dyno but was done in cooler ambient temps.  I will be headed back to that shop in VA Beach in about 3 weeks and will incorporate the cooling system upgrade kit and pursue the other items including a re-cored radiator, 9-blade fan, fan clutch.  Existing fan clutch (and the stock 6-blade fan)  is working but may not be pulling enough air through the radiator.  I'll try that mod. to the 79C thermostat also.  My temp gauge when sitting in traffic will go to the red zone if I let it.  So, while we're in the 3 digit temps at this time I am not driving it locally till I get this under control.  On the highway, at cruise speed, temp is around 180 on the gauge.

[awolff280sl]

If you are running your AC during the summer, you may continue to run into the problem.
Despite employing the remedies mentioned above, my car's temp would slowly creep up when driving in traffic here in Florida during the summer with the AC on (rotary compressor). Even though the needle never got near the red, I was getting stuttering/hesitation when accelerating off of a stop when engine temp was elevated. What cured this (the needle is now always stable at 180 and no stuttering) was an electric fan in front of/straddling both the radiator and condensor. The fan is controlled by either radiator temp and/or compressor activation. The hardest part was finding a large enough pusher fan that would do the job, but thin enough to fit. The fan also helps keep the AC cold and R134 pressure down.

[UJJ]

Andy,
can you please give us more info on the fan you have installed?
Thanks, Urban

[awolff280sl]

Urban,

I ordered from Summit Racing:
Maradyne Fan M113K- http://www.summitracing.com/parts/mar-m113k  The fan can be set up as either puller or pusher, but you need to set it up as a pusher and mount it in front of the radiator and condensor. I mounted the fan flush on the condensor and used rubber spacers to mount across to the radiator. I also had to make a small adjustment to the limit on the hood strap so that the hood does not contact the fan when open.
Adjustable fan controller with radiator probe - http://www.summitracing.com/parts/der-16759

The fan comes with mounting rods which are long plastic "pins" that pass through the radiator and condensor. I used some additional rods that are more heavy duty for extra security- http://www.summitracing.com/parts/aaf-all30085
The fan comes with 4 mounting "feet" or brackets, but I added a few more for additional security - http://www.summitracing.com/parts/spu-ix-30130033  and http://www.summitracing.com/parts/spu-ix-30130017

The fan controller has the option of being temp controlled and/or AC compressor controlled. I used both with an underdash switch to turn on/off compressor control for city driving, hot days, etc.

The fan controller is powered by ignition power so the fan won't run and drain your battery after you turn off the car.
Being overly obsessed with gadgets, I wanted the fan to run for a few minutes after shutting off the car on hot days so as to lower the risk of hot starting problems. I found an timer relay that will power the fan for an adjustable time after the ignition is turned off. http://www.wolstentech.com/products/timedelayrelay/tdr-mf.php    item TDR-PMF

Let me know if you have any questions.

[rwmastel]

I have heard of using electric pusher fans before.  Pictures of your setup would be great, as they would help everyone understand the application of the specific parts listed.  (Great job with part links!)  Thanks

[UJJ]

Thanks Andy
Excellent description. Yes, pictures would be great.
Urban

[awolff280sl]

Here are some pix but you can't see too much. One pic with hood open, one pic closed. The third pic shows 2 of the brackets mounted on the condensor.The plastic mounting rods go through the consensor and radiator. At the very top of the pic you can see the radiator behind the condensor. There are brackets there that you can't see that hold the mounting rods that go through only the radiator using spacers.
Install of the fan does not require hood removal, but the entire front grill comes off.
If there's no condensor, or a smaller one mounted very low, the fan might mount entirely to the radiator.
Otherwise, depending upon the size and location of your condensor, the fan will attach flush to it inferiorly, and superiorly it attaches to the radiator using rubber spacers.
Using the right type of bracket in the right place will give you good stability.
Install is a fidget and each car will be different because of the size and location of the condensor. Obviously, the fan should be centered left-right behind the star, but the exact height may be different, as well as the number of spacers. I was able to rest the center of the fan on the car's frame bar for additional stability.
Be sure to check hood opening with the fan provisionally in place. You'l should be able to gain a few extra millimeters by adjusting the hood strap.
So in my case, the bottom 1/2 of the fan is blowing across the top 1/2 of the condensor and middle of the radiator, and the top 1/2 of the fan blows through the top 1/2 of the radiator across a gap of about an inch. It works.

[TJMart]

I had an overheating problem on my 1970 280SL and I had the original Mercedes bypass kit installed. I have a 79 degree thermostat and ac and no problems now. 

Tony

[awolff280sl]

Tony, good to hear that the bypass kit works for you. Unfortunately, this is only an option for the late 280SL engines with the thermo time switch mounted at the left rear of the head.

[Benz Dr.]

Tony, good to hear that the bypass kit works for you. Unfortunately, this is only an option for the late 280SL engines with the thermo time switch mounted at the left rear of the head.

Early cars rarely have overheating problems unless they're running AC. I've only installed one AC system but I've removed several over the last 10 years. I honestly believe it's a mistake to run these cars with AC. Given the number of remedies required to prevent overheating, it should be clear why I'll never install another one, like ever!

[felix]

Several messages regarding engine overheating mention a Mercedes original bypass kit. Does anyone have a reference or part number for this kit? Any after market kit? Any recipe from an amateur mechanic?
I saw one of the videos on the new website addressing a solution to overheating by means of a kit. Michel Gendron was the featured  presenter but the clip was too short to extract meaningful information, either the full setup or the source if it was a kit.
Thanks, Felix

[WRe]

Hi Felix,
have you read this : www.sl113.org/forums/index.php?topic=19910.msg167415#msg167415  or searched for "heater bypass"?
...WRe

[TJMart]

Felix,

I had mine installed back in April of 2015. I called the MB Classic Center at the time, as I could not find a Mercedes original by-pass kit researching the web. They told me it was no longer available. My mechanic found an original one for me but they are next to impossible to find. Bud's Benz sells an aftermarket one last time I checked.

Tony