Overheating Solution?

[hitch02]

FWIW -

When I bought my '69 280SL about 2 years ago, the cooling system *didn't*.  I was able to get it home at a reasonable temperature by opening up the heater valves (in 90 degree heat!) and maintaining highway speeds.

I went through the entire process:

1 - new thermostat
2 - electric fan: MB part, thin, mounted in front of the condensor, black fan/painted black retaining nut.  Barely visible, but if you look for it through the star, it's there. It is wired to come on with the a/c, and does so very nicely.  Didn't solve the problem.
3 - High efficiency radiator (eBay, $250): Looks stock, car now *rarely* exceeds 180deg, even in this weather.

If anybody wants pictures of the electric fan install, I'm happy to share, but may take a day or two.

-Reed
'69 280SL Silver/Blue
'92 500E

[DavidBrough]

I do have to say that the more I look into this electric water pump idea the more intriguing it gets. Some more useful information at www.mawsolutions.com

I will give them a call when I have time for a good chat and see what they have to say.


David Brough
1969 280SL Auto with A/C

[jeffc280sl]

Interesting ideas from Mawsolutions.  Another thought to consider is installing a smaller diameter pully on the mechanical water pump.  A 20% decrease in pully diameter will create a 25% increase in shaft rpms.

example:

pump pully diameter       engine rpm           waterpump shaft rpm

5 inch                     750                  1200
4 inch                     750                  1500

I think the idea for cooling the engine at idle is to pump more water.  A smaller pully accomplished this.  It would also move more water at higher rpms which could be problematic I suppose.

Jeff C.
1970 280SL 4-speed

[Kenneth Gear]

I struggled with cooling issues for a while before sending my car up to Gernold.  He went through the entire system but the overheating issue was still not completely fixed but then what seemed to work was moving the temp sensor to a different location on the engine block.  

Normally the temp senor is near back, because the car would get warm when stopped at a light but instantly get cooler as soon the it started moving (before coolant from the radiator had a chance to make it to the block), Gernold surmised that perhaps the sensor was in a corner of the engine that was hotter than the rest.  Sure enough, when he moved the sensor to the front of the engine, the temp gauge is much slower to move into red.

If that didn' work his next endeavour was to install an electric pump to circulate coolant when at idle but the problem appears to be solved unless I am stopped for extended periods in very hot weather.

I understand from Gernold that the electric pump solution has worked well for another member of this forum who had been experiencing chronic overheating.



Ken G
1971 280 SL Silver/red
1969 BMW 2800 (sedan)

[waqas]

From the Mawsolutions website, it appears that installing the electrical pump in series with the mechanical pump is feasible (and recommended by them). However, they recommend placing the pump in one of the two radiator hoses (upper or lower). Questions:
 

• If placed in the upper or lower radiator hose, won't the fan be useless (and possibly under risk for burnout) when the thermostat is closed?  
• Of course, if the thermostat is close, additional cooling is not required, so perhaps the fan's cutoff switch should activate at the thermostat temperature?
• Would it not be more useful to attach the pump in series with the heater inlet hose, with a bypass hose fitted from heater inlet to outlet? (bypass courtesy of Jeffc280sl)  

In my car, placing the pump in the lower radiator hose is not really possible-- there's too much stuff there already! (A/C compressor, idle pulleys, belts, etc, etc). This is still a good idea for preventing the engine from heating too much after switch-off.

WAQAS in Austin, Texas

[RBurg]

Was chatting with retired MB mechanic about overheating on the 113's
and also 250 68 - (his personal car).

They (MB Mech) would drill 3 - 4 holes - 1/8 dia in the rim on the

theromstat and this would correct the overheating problem.

Ron - Minnesota
71 280SL Tobacco "O GIGI"
03 525 BMW BlACK/BLACk
97 E420 Silver Mist

[waqas]

Ron,
This would imply that the stock thermostat does not allow enough water flow. If this is true, I wonder why MB has not caught on after 40+ years of the same thermostat design for these cars... surely by now they should have modified the design to allow more flow?

WAQAS in Austin, Texas

[RBurg]

There are many things un said in the big blue book that are not

changed and should have been changed.

 Some methods in the BB make it hard than it really is ex.

change the front coil spring. Follow the book they say remove the 4

bolts on the lower arm.  Much easier - remove the lower bolt from

the king pin.

It's those BULL HEADED GERMANS ( and I am one of them)

Ron - Minnesota
71 280SL Tobacco "O GIGI"
03 525 BMW BlACK/BLACk
97 E420 Silver Mist

[Benz Dr.]

It should be noted that the standard thermostat is 87C for most aplications as I believe this thermostat is used on quite a few different cars in cluding Diesels. The correct thermostat for our cars is 79C which will give you a running temp of about 180F. 87C will get you up into the 195 - 200F range on a hot day while just driving along at a speed of 60 MPH. I had to special order the 79C thermostat and now I have 180F and picked up about 10 PSI oil pressure at idle. Don't let your car run hot for any reason - it WILL warp the head over time.

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

[DavidBrough]

Well, my new engine fan has now arrived and been fitted in place of the standard viscous unit and first impressions are very favorable.

I thought it best to post the results here rather than in the A/C thread even though the change was occasioned by the fitting of A/C.

For a little bit of history, I had been experiencing problems as originally posted here in that my cooling system worked very well until I stopped, at which point things started to get very hot until meaningful progress was again possible.

My original solution was the fitting of a 13inch blower fan to the front of the radiator which solved the problem completely (at least at UK temperatures).

I then had the notion that I wanted to fit A/C which I duly did but had to remove the pusher fan in order to fit the condenser. As a result I was back to square one with an extra heat source to cope with on top. When I purchased the A/C I had already decided to replace the standard engine fan with an electric one but, as the one I needed was not available in the UK I had to wait until yesterday for it to arrive from Italy. In the meantime I tried the heater bypass modification used by jeffc280sl but whilst that did keep the engine cooler on the move it made little difference when stationary on a hot day with temperatures still rising quickly towards the red. So, the electric fan had to work or I was in trouble.

So, I removed the radiator (I’m getting quite good at this now) and sent it to the local radiator shop to have mounting sleeves braised in and a thermostatic switch fitted. At that stage I also decided to source a small fan for the A/C condenser and found an 8 inch blower fan than would just fit. In the end I had to bend the back of some of the grill fins to get it to fit but in it went. I mounted this on a small piece of wood as a spacer on the front cross member to take the weight with the top mounted through the condenser fins on plastic ties which seem to be standard mounts for electric fans. Sorting out the wiring was more trouble than I thought but I made things work in the end with a couple of relays.

The A/C fan now switches on when the A/C is in use and the engine fan cycles in and out when necessary. I currently have a 92/82 thermostatic switch and 79deg engine stat fitted and so far that works OK (26degs today) with the fan staying off whilst on the move and cycling on/off when stationary or in traffic. Need to do a bit more testing in more arduous conditions but my car in standard trim would have overheated today in about 15 minutes if stationary and the fan was able to keep things cool on its own and with the A/C on.

The fans fitted were SPAL units as follows:-

Engine puller fan 16”/385mm part VA18-AP10/C41A

A/C pusher fan 7.5”/190mm part VA14-AP7/C-34S

The A/C fan would only fit directly behind the star with the engine fan having to go high and right on the radiator due to the power steering pump.

I enclose some photos of the installation which may be of interest.

David Brough
1969 280SL Auto with A/C


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[bpossel]

Hi David,

  Your installation looks very neat and clean and well thought out.
Please keep us posted as you drive in stop & go traffic and summer heat.  

  fyi... Memphis heat has been tipping the 100's for the past 2 weeks and looking on Yahoo weather channel, they are predicting 107 by Wed.

  Bring your car here and we can really test it out...

Regards,
Bob

bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

[waqas]

David, nice setup!  I have to say, in my case the heating problem has practically disappeared since I had my radiator re-cored (three row).

The temperatures in Austin are now in the high 90's daily, so I'm getting to drive the car with A/C almost everyday. Without A/C the temp holds at 180, and with A/C, it hovers between 185 and 195 (estimated) in stop and go traffic. When I turn on the heater bypass (with the A/C running), the temp stays between 180 and 185. Of course, the A/C is a bit less effective with the heater bypass enabled...

Sometime this winter, I plan to install Jeff Clute's nifty heater bypass hose solution within the engine compartment (using a couple tee fittings between the heater core inlet and outlet hoses).

Waqas ('Wa-kaas') in Austin, Texas

[DavidBrough]

OK so its summer again and I’m still getting a bit hot and bothered so I decided to try an electric water pump from Davis Craig. www.mawsolutions.com   

I purchased the EWP80 which was a bit of a tight fit but went in eventually and I’ve just wired it to come on with the electric fan, not had a heat wave to properly test it but so far it seems OK.

I think if you wanted to fit one with the standard fan it may take a bit more plumbing but as I have an electric one it slots straight into the bottom hose. Will let you know how I get on when it gets a bit hotter.



David Brough
1969 280SL Auto with A/C & 3.46 Axle




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[waqas]

Looks great.  Did you mount the pump to something, or is it simply 'floating' between the two ends of the cooling hose?

Please keep us posted as to performance.

[DavidBrough]

It sort of floats in the bottom hose but rests quite firmly on the air filter inner panel due to space constraints. At this stage I have put some rubber in between to stop vibration damage and will have to keep an eye on it.


David Brough
1969 280SL Auto with A/C and 3.46 Axle

[Benz Dr.]

The best car is the 250SL. Lots of cooling room in the block and the largest rad of all 3 cars.
Try using a 79C thermostat. My car runs at or below 180F even on the hottest day. Excessive heat is VERY bad for these engines.

[DavidBrough]

Hi Dan,

I have the 79 deg thermostat and whilst I have never actually overheated I’m not comfortable about heavy traffic on hot days.

Only real test at this stage has been to let the engine get nice and hot then switch it off which usually then adds a good few extra degrees and puts the gauge almost onto the mark above 180 and just below the red, but 10/15 seconds of the electric fan and pump together has it straight back to 180.

David Brough
1969 280SL Auto with A/C & 3.46 Axle

[Q45Denver]

How much power are the two fans drawing?  Did you have to upgrade your alternator?

[Longtooth]

Is this stationary in warm weather "overheating" problem particular to the 280SL?  

My 250SL with 14k miles since rebuild, plus recoring radiator, doesn't have an overheating problem and this is in 100F+ weather and after high speed (80mph) driving and coming to a stop right off the freeway.  Fan clutch engages sometimes after coming to stop after high speed freeway driving in 100F+ weather... but temperature gage never even comes close to the red area.  

Since 250SL and 280SL engine blocks differ only in bore/stroke, and if bore's larger on the 280SL then cylinder cooling efficiency is better than the 250SL anyway (thinner walls means faster and more efficient tranfer to heat to water passages).

I submit therefore that any overheating problems means something's broke ---- pump wear causing insufficient coolant flow, or scale build-up in water passages in block or radiator increasing resistance to coolant flow... hence reduction in coolant flow volume, or oil pump efficiency loss (even if oil pressure gage says all's ok).  

If overheating's a particular problem on 280SL's then what is the design difference that pushes the 280SL over the edge compared to a 250SL?  Recall that MB shipped a ton of the W113's to climates much hotter than Germany... not insignificantly a higher proportion geographically to US SoCal area where summer time temps are relatively high all the time.  If overheating was an issue with reliability or function MB would have had to change designs to fix this by the time the 250SL and 280SL especially started rolling off the lines.

All the work/effort/modifications to improve coolant volume or air volume over radiator seems to me to be masking some other problem(s) that need to be corrected anyway.  If engine's producing more heat than it should be for the designed water pump volume flow and radiator (heat exchange), then it means engine's frictional heat sources are exceeding the design limits... i.e. bearing wear and/or cylinder wall wear.

[DavidBrough]

Hi Werner,

I’m not actually sure what the amps are for each fan but I do have three. The main fan a slimline Spal must be about 10/15 with the small condenser fan being about 5/10 and the evaporator fan about 10/15 perhaps. I do have an uprated alternator fitted but don’t know its rating off hand but I do tend to plug in a trickle charger when the car’s not in use.

Longtooth,

I agree with your sentiments but it does seem that the early 280’s were quite susceptible to getting a bit hot and bothered and MB changed the head design on later cars which seemed to cure the problem, they did bring out a kit for the early cars but those that have tried it say it’s not much good and very expensive. I have replaced everything possible in mine and added numerous upgrades but all to little avail. As I don’t think MB changed the pump design it seems to be more a circulation problem which, so far at least, the electric pump seems to have resolved. Having said that it also seems unlikely that my car behaved this way when new and I do know that the problem is not A/C related as I had the same issue before it was fitted so something must have changed over the years but quite what, apart from fuel, I don’t know.


David Brough
1969 280SL Auto with A/C & 3.46 Axle

[Q45Denver]

quote:Originally posted by Benz Dr.

The best car is the 250SL. Lots of cooling room in the block and the largest rad of all 3 cars.
Try using a 79C thermostat. My car runs at or below 180F even on the hottest day. Excessive heat is VERY bad for these engines.

Does the 250SL have an oil cooler?  Is the cooler controlled thermostatically?  Maybe the bigger radiator is the answer?

[Q45Denver]

quote:Originally posted by DavidBrough

Hi Werner,

I’m not actually sure what the amps are for each fan but I do have three. The main fan a slimline Spal must be about 10/15 with the small condenser fan being about 5/10 and the evaporator fan about 10/15 perhaps. I do have an uprated alternator fitted but don’t know its rating off hand but I do tend to plug in a trickle charger when the car’s not in use.

David Brough
1969 280SL Auto with A/C & 3.46 Axle

Curious about the evaporator fan.  You have that inside under the dash?

[Dick M]

The heater bypass isn't pretty but works well on my 280SL.. keeps the temp right around the 180 deg. mark, even on hot days in traffic or mountains.  

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I think I got the idea from Jeff C.  

[DavidBrough]

Dick,

When I fitted my A/C I also fitted a heater bypass, exactly the same as yours, and the Spal fan on the radiator in place of the viscous unit on the basis that together they would solve the problem but still no joy. What I don’t know however is if they would cure my problem without A/C. I did take a bit of a punt when fitting the A/C knowing I had an issue but felt the problem must be curable.

It has been a bit warmer over here today and I left the car ticking over long enough to overcome the electric fan and start to get gradually hotter up to the middle of the two marks on and above 180 then switched on the pump and bingo down to 180 again, I just hope it continues to do the same when temperatures get a even hotter. For the time being I have wired the electric pump to a manual switch so I can monitor what is happening and if all proves OK I will link it back into the automatic switch for the fan.

Werner,

The evaporator fan is the standard blower that came with the Buds underdash unit and I think oil coolers were only fitted as standard on 280’s. At one stage I did think about looking at either a larger or an additional oil cooler as they can make a lot of difference, hopefull I won't need to go that far.



David Brough
1969 280 SL Auto with A/C & 3.46 Axle

[Q45Denver]

Thanks for the info. I think a larger oil cooler might work but it gets pretty cold here winters so I would need to install a thermostat. Its been pretty hot here recently and I over heated my M130 engine.  Now it smokes badly (oil smoke) when first started after sitting awhile. I just had a valve job a couple thousand miles ago. Don't want to fix it until I determine what caused the problem and don't want to drive it while smoking. I already had the radiator rodded out and that didn't seem to make much difference. The car does not have a condenser fan so that will be the next step. Also I might go with a rotary AC compressor instead of the stock York compressor.  Wouldn't the heater bypass cause the cabin temperature to get uncomfortable?

 

quote:Originally posted by DavidBrough

Werner,

The evaporator fan is the standard blower that came with the Buds underdash unit and I think oil coolers were only fitted as standard on 280’s. At one stage I did think about looking at either a larger or an additional oil cooler as they can make a lot of difference, hopefull I won't need to go that far.



David Brough
1969 280 SL Auto with A/C & 3.46 Axle