70 280SL engine overheating

[Benz Dr.]

It's like this....

The 127,129 and M130 engines are all the same size - on the outside. They all started from the original 220SE from about 1958. A 220S/SE has a huge rad and those cars never overheat as a rule and they have a small cooling fan compared to a 280SL. Even the 230SL has a small fan ( similar to the 220SE )

So, how did they increase engine size? Well, from the 220SE to the 230SL they used larger pistons and increased compression ratio. From the 230SL to the 250SL they increased the length of the stroke but the bore stayed the same as did the radiator size. The 250SL also had an oil cooler - these things are bullet proof.
The 280SL had to have the cylinders enlarged and moved closer together which meant less area for cooling water. This was improved by adding a number of extra cooling passages but the smaller rad offers less cooling. The air oil cooler only really works when the car is moving at speed and no air is moving under the car to cool the oil pan. Add to this A/C and you have extra heat that has nowhere to go but into already hot parts. All that A/C gear tends to restrict air flow around  less than optimal cooling.
The late cars have distributor timing controls that retard ignition which will also make the engine run hotter. There is a 100C thermo switch that will shut off the vacuum and advance the ignition to help cool the engine a bit and I think the A/C is plummed into this system so that it shuts off ignition retard with the A/C on. A lot of time this stuff isn't working or working right. A lower temp switch than 100C might be a good idea.
As I've said before, people expect too much from these old cars. The 280SL engine was a highly modifed 220SE engine - probably a little bit beyond where they should have gone. It's not unreasonable for this engine to run hot on a hot day when the design was right on the edge to begin with.

So, in summmary, the more you stress an engine the hotter it will run. The more you add to the engine the hotter it will run. A/C and US regs were after thoughts to the design and worked OK under ideal conditions when conditions were ideal. How often is that 35 years after the fact?

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[Michel MB280SL]

  Thank you very much to each and all that have taken the time to share info on this burning topic.  Here is my plan;
1- Re-verify the adjustments for valves, ignition timing, dwell angle, CO test for fuel mixture and strobe timing check.
2- Flush/clean engine and refill.  Ensure no air bubble remain in the system.

If this is not satisfactory, I plan to add the Pertronix or Crane electronic ignition and then finally, the M-B engine head bypass modification for USA 280SL.

Hopefully, this will bring the car performance to a level that I will feel comfortable with even if it isn't perfect.  So I'm not ready to give up yet.  I'm from Montreal, Canada. We get two and a half months with damp 80 to 90 degree weather and are forced to drive in slow (mostly stopped)heavy traffic that bring hell to our driving enjoyment.

I'll keep the group posted on the results.

Note: Special thanks to Dr Benz (Dan Caron) for his expert advice.

[rwmastel]

quote:Originally posted by Michel MB280SL

Here is my plan;
1- Re-verify the adjustments for valves, ignition timing, dwell angle, CO test for fuel mixture and strobe timing check.
2- Flush/clean engine and refill.  Ensure no air bubble remain in the system.

If this is not satisfactory, I plan to add the Pertronix or Crane electronic ignition and then finally, the M-B engine head bypass modification for USA 280SL.

You might want to start with the M-B engine head bypass modification for USA 280SL.  I have no personal experience with it, but many here seem to think it's a big help.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[Benz Dr.]

Do you think you can make it down here for '' The meeting of the clans '' on July 29th - 30th? A few people from the Montreal area are coming. Richard from Shawville and a guy with a 190SL is supposed to be coming. How about you?

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[Raymond]

Cees, Come on! 86F is a heat wave?  Here in Florida we're just getting comfortable.  Today it was a balmy 92F.  Positively cool for July.

Okay I admit I wanted a jacket when we rode in your fabulous 280 last month.  It was in the mid 60s if I recall.  

To all you other folks, if you find yourself in Amsterdam, Mr. Klumper's car is a great example of how our cars should run.  Smooth as silk, goes when you kick it, and an automatic transmission that shifts so smoothly you can't believe it's a Pagoda.  A car that well tuned doesn't overheat.



Ray
'68 280SL 4-spd Coupe

[Michel MB280SL]

quote:Originally posted by Benz Dr.

Do you think you can make it down here for '' The meeting of the clans '' on July 29th - 30th? A few people from the Montreal area are coming. Richard from Shawville and a guy with a 190SL is supposed to be coming. How about you?

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

Thank you very much Dan.  I had seen the invite yesterday and admit I would have loved to go.  Unfortunately, I have an engagement for that very weekend here with my sisters.  I will certainly make every effort to participate in one of the M-B Club event this summer and hope to meet you there.

I wish you well and prompt recovery following your operation.

Good luck with the event.  It seems it will be well sought after.

[ja17]

Hello Michel,
If your car did not overheat before the work was done you may have some issues to deal with. It could be a big problem like the wrong head gasket. There is an early and a late head gasket for the 280 series M130 engine. See "cylinder head chart". Or something else has gone bad like the fan clutch or some kind of blockage. Its hard to diagnose long distance without knowing all the facts.

I used to service one 1971 280 SL many years ago, nearly new, it was just out of warranty. It was a USA model with AC and it did want to overheat in stop and go traffic with AC on in very warm weather. Some owners have added heavy duty radiators to cure the problem. Most of the time with non AC cars, something else just needs fixed.

Joe Alexander
Blacklick, Ohio

[Benz Dr.]

I know about the two different head gaskets on the 280SL. If you use the late gasket on the early engine it will burn through in short order and fill the oil pan with water.
This happened to me once which is why I always start a rebuild on pure water.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[Sphe]

Wow, I was never aware of these issues. Hopefully moving to Florida won't cause problems for me when I finally get my 230SL on the road... Someday!

Eugene
1965 230SL, Max Speed: Zero

[n/a]

Gentlemen;
I've not had any overheating with my 280SL, but if I did, I would add auxiliary electric fans or replace fan with one with more blades...by the way, is there summer/winter theromostat choices for these cars? The elctric fans, especially directed at the oil cooler, should make a big difference...as i understand it, the Porche is mistakenly called air cooled, when in fact it has an oil intercooler so is really very dependant on the oil radiator...
R/
Joe
 

[jeffc280sl]

I've been looking at the MB instructions for improving cooling via a bypass kit that utilizes the thermo time switch opening in the head to recycle hot water out and into the radiator.  On cylinder to the front of this opening is the heater core hose port in the head.  You may have turned your heater on during very hot days to cycle hot water through the heater core and reduce engine temps.  After reading a post from someone else I decided to bypass the heater core entirely by connecting removing hoses from the heater core and connecting them together.  This seams to have improved the overall cooling of the engine quite nicely.  It is very hot in DC these days and I took a ride in the heat today and have recorded the results in the attached image.  This is preliminary.  I have ordered two radiator hose tee fittings.  I have plans to install the tee fittings in the heater hoses and route hot head water on a full time basis around the heater core.  When heat is needed in the cabin I'll open the heater core valve and see is sufficient hot water will flow though the heater core to warm the cabin.  A backup plan may involve using one tee in the heater hose leaving the head and adding a second tee in the lower radiator hose insted of the output heater hose.  Connecting the head output directly to the lower radiator hose is similar to the Mb instructions and may improve cooloing a little more.

 

Jeff C.
1970 280SL 4-speed

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[jeffc280sl]

T fittings arrived and have been installed.  It's hot again in DC, around 95F.  Here are a couple of pics which show the temp gauge and bypass hose kit. The temp in the engine compartment was about 121F when I took these pics. Engine temperature has been reduced significantly.  Turned on the heater valve and received plenty of heat in the cabin.  It's hot outside so a better test will be taken in the winter sometime to see if heating has been negatively effected.

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Jeff C.
1970 280SL 4-speed

[JPMOSE]

Just to pipe in with another case:  I've been driving my 250SL all week to work, as my 560SL is in the shop.  I don't have A/C (of all weeks for the 560SL to act up!) and it's been in the high 90's in Atlanta.  When I leave the office at 5PM, I typically drive down the freeway at 80 MPH and come to a near stand still when I hit Midtown.  For the next 10 - 15 minutes I am moving at 5-10 MPH.  Even in this heat, my car doesn't quite reach to next bar above 180.  The radiator hasn't been recored since 1978.  I have a container of Wet Wetter and have been too forgetful to add it.

Sounds like the emissions of the later 280SLs may be the culprit.  I met a couple with a late '70 280SL and they complained of the overheating at idle too.

I hope you come up with the right solution!

Best Regards,

J. P. Mose
1968 250SL
1987 560SL

[webmig]

Although this is an old topic, I do want to try to get you all backinto it.

I have a 1970 280SL, it never ran hot, it never overheated in heavy hot traffic.   Last week I had it serviced and tuned up and yes...   Now and for the first time my car overheats!

I used to be more enthusiastic and allays did the tune ups myselve, I used to write down every measurment that resulted (vaccum readings, at idle as well as on various rpms, distributor timings with and without the vacuum line connected, etc) and used those settings for every new tune up with good results every time.    I wrote all those personal tips on one of those Haynes manuals, but for some reason my manual got lost.

I lost it and that is why I had someone else do this last tune up.   The tune up seems and feels perfect but the thing with the temperature is something new.

[ja17]

Hello Miguel,

The thermostats should never be removed and left out,  on these engines.  This will cause the engine to run hotter.  Setting the timing out of specs can also cause the engine to run hot.  Always a chance the fan clutch may have gone bad.

[webmig]

Hello Joe and thanks,

I do have the thermostat installed, since the car had never had the overheating problem I never had the interest of messing with it.

I'll check the fan clutch.

If your car does not overheat, do you know the exact readings you get at Idle and at 1500rpm with and without the advance connected?   I know the question doesn't make much sense since there is a few degree adjustment range that we can use for both rpms but I would like to set this exactly as someone who has no overheating problems an then move on to other adjustments.   I also want to check if my advance is turning the same degrees as one which is running correctly.

Miguel

[twistedtree]

Could the mechanic have set the timing using the wrong scale on the front pulley?  I think the result would be a grossly advanced spark.  But you say the car runs OK, and I would think such a miss-adjustment would be noticeable.  Anyway, it's just a thought.

[Cees Klumper]

One thing I would do is go back to the mechanic who did the tune-up and ask him exactly which things he did that could affect the engine temperature. Like, did he replace the coolant? Air in the system? Ignition timing? Explain to him why you are asking and try to figure out together what may explain this. Please keep us posted, this is of interest to all of us.

[Cees Klumper]

Ps in 2001 I was in Mexico city and I saw a Pagoda parked roadside. Could this have been yours? I believe it was white but not 100% sure.

[Benz Dr.]

Reading back through all of the posts in this tread. I found a couple of things wrong in my statements - we all learn along the way, right?

 The 230SL and 250SL don't share the same radiator size. The 250 is much larger than a 230 and is the largest rad used in the three different models. 250's almost never overheat because the rad is so large on those cars.
The 280 has the same rad cradle size as a 250 but some of this space is used up by the oil cooler. The rad on a 280SL is about the same size as a 230SL rad so it's really too small for the engine. Add to this the fact that there's too little space around the cylinders for much coolant to run around through the the block on a 280SL and anything that limits normal cooling will have instant results.

If you run AC on a late 280SL engine you should have a fan shroud if you don't already have one. Make sure your engine is clean and particularly around the front of the engine. If it's covered with grease and oil, power wash this stuff off the engine.

My engine puts out about the same HP as a typical 280 engine but it never runs hot. Make sure you use the 79C thermostat. The other available thermostat is 87C and it WILL make a late 280SL engine over heat. This is the thermostat I have to run on my car because it tends to run too cold otherwise.

I used a sedan cooling fan on my car. I didn't actually realise this until someone asked for a certain sized fan for a 113 and then I noticed that my fan had blades that are almost an inch longer than the stock fan. This larger fan just fits on my 230SL and may not fit at all on the 250 and 280 SL's. In fact, I'd be inclinded to say it doesn't fit which is too bad because it moves a lot more air. The sedan model ( 280SE ) has more room in the engine bay but it's also a heavier car so they took advantage of this extra room by providing this larger fan for needed cooling.

The oiginal 113 was designed to be a 230SL and everything after that was a further modification on some sort of after thought. By the time the 280SL arrived the cooling capacity was right on the edge and anything like AC was never really going to be a good idea. When do you use AC? When it's hot outside, right?

I remove every AC system from 280SL's that I do a rebuild on if I can talk the owner ino it. Almost everyone says yes citing the fact that once the engine starts to overheat, they have to shut it off which makes AC basically useless.

In short, you will warp the head if you run the engine hot over repeated cylcles, or one very long one. Run your engine ouside of its design paremeters, and you will pay for it.

[webmig]

Joe,

You were right, the fan clutch is not working properly,

It's kind of strange that it would stop running properly during a tune-up procedure, I think it has been going bad day by day, that I did not notice it maybe because of the cold weather we had on the past months.   Also some tune-up missadjustment just made bad things work alltoghether.

I didn't mention but I also had the air cond serviced with new gas that same day.   Overheating was obtained without usng the air cond.

Cees,
Yes, white -light Ivory with tan interiors

Mig