Fan Clutch, Fan and Radiator: Cooling Test Results

[Atazman]

My 250 SL is lacking on cooling capacity. 

Some pertinent information:
•   All testing done with A/C system set for max cooling.
•   I have a 6-blade metal fan and a fan clutch.
•   The fan clutch allows the fan blades to rotate freely after shutting the engine down when the coolant temperature is 220 Deg. F.  Seems to me the fan should not rotate freely when the engine is this hot.
•   With engine running, I could not stop the fan using a newspaper to slow it down; not sure how much resistance the newspaper had to stopping the fan though.
•   I never hear or feel anything to give a clue that the fan clutch is engaging.
•   At highway speeds of 70 mph on a 95 Deg. F. day, the temperature gauge read about 212 Deg. F. (at white dot) after just 15 miles. This makes me question whether the radiator is defective.
•   At idle with the A/C at max cooling on a 75 Deg. day., engine temperature will go above 212 Deg. F. (white dot) within 10-15 minutes.
•   At idle with A/C on max cooling, I saw only a 11 Deg. F. temperature difference between the top of the radiator and the lower quadrant of the radiator.  This suggests to me there is not enough air moving through the radiator due either to a defective clutch or an inadequate fan.

So here are my questions for possibly resolving my cooling problem:

1)  My fan clutch rotates freely even when the engine is "hot".  Is this a sufficient test to say the clutch needs replacement?  If not, what is a better test?

2)  My fan is 6-blade.  I know there are 9-blade plastic fans available.  Has anyone seen a difference in cooling when making a change to the 9-blade fan?

3)  Coolant temperature going too high on freeway drives suggests (to me) the radiator is either defective or undersized.  Do you agree?

4)  If the fan clutch is defective, would this add to my cooling problem at freeway speeds?

5)  I'm running about 38 Deg. BTDC on my timing at 3,000 rpm.  If I back off on the timing to something around 30-32 Deg. BTDC, will this timing change decrease engine temperature?

6)  If a radiator change is needed, are we able to fit a "3-row" or a "4-row"?

I know there are special “agents” for coolant.  I would prefer solving my problem with hardware changes if possible even if I change all three……. clutch, fan, and radiator.

Thanks to all for your patience on this long post. 

[kampala]

When my pagoda was running hot the first question the radiator shop asked was does it get hot at highway speeds?   If the answer is YES, they said 99% of the time it's the radiator.   The airflow at speed rules out the fan.  They said at that point they fix radiator and then if needed chase any other issues.   In my case they were 100% correct.   Click link to Movie of water-flow in their shop before they fixed the radiator - flow is lacking in the center.    Link is to Google photos. 

https://photos.app.goo.gl/1aL0M94z8dPhbbfY2

Note: Most will tell you otherwise, but this particular shop's opinion is that the two core is better than 3 core, but since my core needed replacement, vs rodding out, they could not locate a two core that would fit so they put a 3 core instead.  no issues. 

[rgafitanu@gmail.com]

I don't think your fan clutch is defective. If it is a viscous clutch, the fan will spin after shutting down the engine. If you cannot stop it with a newspaper may not be a bad thing. That means it is strong and provides good air flow. I changed my solid mounted 4 blades fan to viscous clutch 9 blades and I cannot say that I see a difference in temperature. I am sure it is a better option. However, I have a 230 engine which may be slightly cooler than a 250.

[Benz Dr.]

A 250SL has the largest rad in terms of actual size so in theory it should make your engine run coolest. 250SL's also have an oil cooler which should help in overall engine cooling. I tested mine once and the oil temperature going into the cooler was about 20 degrees higher than the oil on the return side so I believe it works as intended.

[lurtch]

Hi Don,

You have done an excellent job troubleshooting the problem, but I suggest you might have to dig a little deeper.

The series of pencil-sized coolant passages between the cylinders have a tendency to corrode. Admittedly, there were other problems with my original engine, but this might be starting to happen in yours.


Larry in CA

[Benz Dr.]

Very common problem caused by acidic coolant. This can be repaired by welding new aluminium into the holes after all of the corroded material is removed. Water diverters are available but you should carefully note which way they point before removing so they can be installed in the same direction. I've fixed quite a few heads like this one but some were not cost effective so I replaced some of them.

[Jordan]

Don, I would start with easy and simple first.  Check your rad.  Get yourself a laser temperature gun from your local hardward store if you don't have one.  Relatively inexpensive.  Take your car for a drive to get it good and hot, return home, and while the engine idles take temp reading across and up and down the rad to see what the temps are.  If there is a cold spot, you have found your blockage.  You can also use the laser on the engine and coolant hoses to see what the temperatures to see if and where you have hot and cold spots.

My engine use to run just below the white dot when highway driving.  On a hot day it would climb to the white dot.  I ended up replacing the 2 core with 3 and replaced the water pump while I was at it.  Temp now pegs at 80C (180F) consistently, even when highway driving.

[Atazman]

First, thanks to everyone who has commented (Kampala, Rau G, Benz Dr., Lurtch, and Jordan)!

I had my head re-built in 2009 with less than 15,000 miles on it, so I’m hopeful the corrosion bug is not eating away.

As suggested, I did a temperature profile across my radiator and I did find the passenger side of the radiator much cooler than the rest (maybe 30-40 deg.).  Just hope my temperature gun reads correctly.  Based on this test, my experience of overheating at freeway speeds, and your success with a 3-core radiator, I will move ahead with taking mine to a shop for inspection and testing.  It has had nothing done to it in the 35 years I have owned the car.

Further, I am concluding that my fan clutch is not as efficient as it should be.  Today, I held the fan stationary until my temperature got to the 212 Deg. F. mark.  I released the fan and it did bring the temperature down a few degrees……but not down to 180 Deg F.  I then drove the car on the freeway (w/o my A/C going) and the air moving across the radiator brought it down to 180 Deg. F.  This is on a 70 Deg. F. day.  Granted….. a poor radiator would cause cooling problems at idle too, but I cannot separate the effects from the fan and the radiator.  I’ll just replace the fan clutch at the same time.  Like the radiator, I believe it is the original.

So far, no one has quantified the benefits of going from a 6-blade to a 9-blade fan.  Maybe there is no benefit.  I’m still in a quandary as to whether I want to go for the 9-blade fan.

And lastly, I was hoping someone would give me an idea of whether running the timing at 38 Deg. BTDC will cause the engine to run hotter than if the timing is set at say 30-32 Deg. BTDC.  If it benefits the cooling aspect, I’m willing to lose a little performance and gas mileage by retarding the timing a few degrees.

Again….. I thank everyone for helping me out.

[WRe]

Hi,
did you ever flush your cooling system with citric acid, as described in MB WIS, here for W126: http://www.w126.kistinger.com/Kuehlsystem_reinigen.htm. It's a very cheap but effective method.
Remove your coolant and thermostat, open heater lever, flush the system with clear water to remove any coolant left, mix clear water with citric acid (1.5 kg/10l) and fill it in your cooling system, start your engine and bring it to temperature, leave it there for some hours, remove the mixture and flush again with clear water. During summer I would leave the clear water for some time in the system before I remove it again and refill it with anti-freeze.
Here a similar thread: https://www.sl113.org/forums/index.php?topic=6385.msg39768#msg39768.
...WRe

[Atazman]

WRe.....

I have never flushed with citric acid but will consider doing so.  Wish the article you referenced could be converted to English.

Right now my plan is to replace the fan clutch and convert to a 9-blade fan.  Then, I will re-evaluate the need for either flushing my radiator myself or taking it to a radiator shop for either rodding it out or replacing the core with more rows.

Thanks to everyone!

[WRe]

Hi Don,
try Google Translator or ...
...WRe

[Atazman]

I chose your "or" option, WRe.  Thank you for making the translation.

[Atazman]

Hi WRe...

I intended to let you know I never did the citric acid flush, but I forgot.  Sorry about that!

Anyway, my reason for not doing the flush along with all the other work I did was because I replaced the engine in 1983 and since that time it has been well maintained with regular antifreeze changes and regular flushes.  And the engine has relatively few miles on it.  That was my logic...right or wrong.

I did post elsewhere that my cooling problem has been solved with changing out radiator, viscous clutch, fan, and thermostat.

Thanks for your input along the way.

[Benz Dr.]

First, thanks to everyone who has commented (Kampala, Rau G, Benz Dr., Lurtch, and Jordan)!

I had my head re-built in 2009 with less than 15,000 miles on it, so I’m hopeful the corrosion bug is not eating away.

As suggested, I did a temperature profile across my radiator and I did find the passenger side of the radiator much cooler than the rest (maybe 30-40 deg.).  Just hope my temperature gun reads correctly.  Based on this test, my experience of overheating at freeway speeds, and your success with a 3-core radiator, I will move ahead with taking mine to a shop for inspection and testing.  It has had nothing done to it in the 35 years I have owned the car.

Further, I am concluding that my fan clutch is not as efficient as it should be.  Today, I held the fan stationary until my temperature got to the 212 Deg. F. mark.  I released the fan and it did bring the temperature down a few degrees……but not down to 180 Deg F.  I then drove the car on the freeway (w/o my A/C going) and the air moving across the radiator brought it down to 180 Deg. F.  This is on a 70 Deg. F. day.  Granted….. a poor radiator would cause cooling problems at idle too, but I cannot separate the effects from the fan and the radiator.  I’ll just replace the fan clutch at the same time.  Like the radiator, I believe it is the original.

So far, no one has quantified the benefits of going from a 6-blade to a 9-blade fan.  Maybe there is no benefit.  I’m still in a quandary as to whether I want to go for the 9-blade fan.

And lastly, I was hoping someone would give me an idea of whether running the timing at 38 Deg. BTDC will cause the engine to run hotter than if the timing is set at say 30-32 Deg. BTDC.  If it benefits the cooling aspect, I’m willing to lose a little performance and gas mileage by retarding the timing a few degrees.

Again….. I thank everyone for helping me out.

Run your ignition timing at 38 degrees BTDC with everything connected. Late ignition timing can cause overheating problems.

[Atazman]

Thank you, Benz Dr.

You answered my question ....... I needed confirmation 38 Deg. was not a little too far advanced for optimum cooling.

Appreciate your response.

[Atazman]

Several have suggested the importance of the viscous clutch working properly to achieve low-speed cooling.  Has anyone made an "adapter" to eliminate the viscous clutch and run the fan direct at water pump speed?  Should provide additional low-speed cooling, although at the expense of loosing some horsepower.

I understand...... many are totally against deviating from how the car left the factory.

[mbzse]

.../...run the fan direct at water pump speed.../...

This was the setup for the M127 engine (230SL)  No viscous clutch, four blade (plastic) fan

[Atazman]

Very interesting!  Looks like the viscous clutch could be eliminated very easily.

Thanks for confirming the question was not totally ridiculous.

[mbzse]

.../...the importance of the viscous clutch working properly to achieve low-speed cooling.../...

This is a useful explanation, it illustrates how the viscous clutch works in our Pagoda cars:
https://www.youtube.com/watch?v=UwM4OqsLek4

[Tyler S]

The viscus clutch is needed because the increased displacement of the m127 and m129 engines rendered the 4 blade fan obsolete for air flow capacity at idle. A 6 blade fan is used to overcome this. However a 6 blade fan is extremely noisy at higher rpm. It’ll sound like a garbage truck without the clutch/coupling