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The auxiliary water pump is used in the ACCII and ACCIII climate control system which the '77 should not have. It has nothing to do with engine cooling.
 

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Thanks. I installed a BEHR thermostat. Would a WAHLER work better?
Also, I understand there may be an auxiliary water pump (https://www.autohausaz.com/pn/0008356964OE) - Where is this component located?
It could be as simple as tstat not quite being fitted as per service manual?

Can it be that a thermostat fitted is similar to original but still the wrong pn?
Perhaps try another make.

I believe that the poor radiator flow (as per above) would be indicated by cold bottom tank hose and extremely hot top hose.

Here's the link to the 107 Servic eManual.
It stopped working for some years manufacture but it works for similar years (e.g. 1980)
 

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Discussion Starter #24
Aux Water Pump

The auxiliary water pump is used in the ACCII and ACCIII climate control system which the '77 should not have. It has nothing to do with engine cooling.
Thank you for clarifying this for me. It certainly explains why I never found it.
 

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Discussion Starter #25
Thermostat

I'll risk repeating myself, above bold text confirms my thought on thermostat not doing its job of diverting sufficient coolant to the radiator (cabin heating runs on coolant straight from the engine, before thermostat). Thus increased airflow through the radiator will not help

see the coolant flow diagramme and it will make it easier to comprehend as to why thermostat can keep otherwise perfect engine hot - by not diverting enough coolant to the radiator making everything appear as functional but actually being faulty!

In depth:
https://www.startekinfo.com/StarTek/outside/11883/PROGRAM/Engine/107/M117_56/20-005.pdf

Thermostat change over (generic image):
Dlenka;

Thank you for these images. I will check the bottom radiator hose the next time I take the car for a spin.
I do know that the top hose gets hot as hell and becomes pressurized. Would this still be the case if the thermostat is only partially open? Just curious.

I do want to thank everyone for posting here. From everything you guys have contributed, I suspect my problem is either a thermostat that does not open all the way of a 42 year old CAT that has restricted airflow.

I am curious about one thing: Has anyone here taken IR Laser Gun temp readings of their exhaust manifolds when the car is at operating temperature or hotter? Mine are in the mid 400's F and I just wondered what NORMAL should be.
 

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Discussion Starter #26
Not sure if it applies to your year but on mine I was seeing the same thing (high temp related to high rpm).

Setting ignition timing from factory specs (can’t even remember what that is) to 5 BTDC helped mine.


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How high were the temps?
 

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Dlenka;

Thank you for these images. I will check the bottom radiator hose the next time I take the car for a spin.
I do know that the top hose gets hot as hell and becomes pressurized.
Check the bottom radiator hose... make sure it isn't collapsing under the vacuum created by the water pump. Lower radiator hoses generally have a coil or some type of internal reinforcement to prevent collapse under the vacuum created by the water pump. The lower radiator hose should be cooler (not cool, just cooler) than the upper radiator hose.
 

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Discussion Starter #29
Check the bottom radiator hose... make sure it isn't collapsing under the vacuum created by the water pump. Lower radiator hoses generally have a coil or some type of internal reinforcement to prevent collapse under the vacuum created by the water pump. The lower radiator hose should be cooler (not cool, just cooler) than the upper radiator hose.
The old bottom hose did not have a coil - neither doesthe new one I put in a few months ago. I never saw this in the parts list on AUTIHAUSAZ, FCPEURO, or anywhere else. Did these cars come with one?
 

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The only thing I did not hear you say was...did you compare the engine temp with your laser thermometer AT the engine temp sensor and compare to cluster temp gauge reading?
It is a single pin sensor at the drivers rear of the drivers cyl head. Almost the hottest part of the engine.
If that is good...I can make a suggestion but I hate that you have already replaced your radiator.
If your new radiator is a copper radiator A good radiator shop can re-core the radiator with a core that has larger cooling tubes.
It provides an additional 200 to 300 btu's of heat removal.
It is a good fix.
If this is a consideration you probably can get most of your new radiator money back on Ebay if it is a copper/OE radiator.
Michael
 

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I was having a similar problem. I replaced the fan clutch ( with the cheapest one I could find ), which helped some. But was still not quite where I would like it. I put on a new auxiliary fan and added a switch so I can turn it on when I want. But, as you noted the aux fan does not do a lot. At first I thought I was running lean but it turns out I was running a bit rich. After checking the timing and adjusting the mixture screw in the FD and the air valve just a little at a time,I've had a lot of improvement. I think getting the idle smoothed out and running where it should helped the heat rise while at idle in traffic. Being responsible I would say get your combustion gas analyzed, before adjusting. But, I didn't,just took baby steps. Adjust,drive a few days, adjust, etc. Small adjustments,Like 1/8of a turn or less.The new fan clutch took care of the problem at highway speeds. I may still tweak a bit more. But, I am in Maine and you are in Arizona so, I ( don't ) feel your pain....Not saying this your solution but you have tried a number of things and maybe this will help although it seems you may possibly need a radiator with more cooling capacity... I was going to do a coolant flush,but wanted to see if I could get improvement before opening another can of worms...
 

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Discussion Starter #32
The only thing I did not hear you say was...did you compare the engine temp with your laser thermometer AT the engine temp sensor and compare to cluster temp gauge reading?
It is a single pin sensor at the drivers rear of the drivers cyl head. Almost the hottest part of the engine.
If that is good...I can make a suggestion but I hate that you have already replaced your radiator.
If your new radiator is a copper radiator A good radiator shop can re-core the radiator with a core that has larger cooling tubes.
It provides an additional 200 to 300 btu's of heat removal.
It is a good fix.
If this is a consideration you probably can get most of your new radiator money back on Ebay if it is a copper/OE radiator.
Michael
Hello Silver.
I have not pointed the laser at the temp sender. I have pointed it at the thermostat housing and compared that to the top of the radiator. If the top of the radiator is close to 220F, the thermostat housing is close to 212F. Seeing that and observing the aux fan kicks in around those readings convinced me that the gauge readings were "close enough"to being accurate. Besides, the HEAT coming out of the engine compartment is hard to ignore.

I have the old radiator and could go that route, but I am apprehensive about spending the money without knowing if that will alleviate the problem. Besides, I really suspect that what I have is an engine generating more heat than it is supposed to as opposed to a malfunctioning cooling system. I would really like to identify the cause.

The problem I am facing is that shops here like to tell you they don't touch cars manufactured before 1996. Goody's Automotive will work on them but they tell me that the needle at 212F is "Perfect", "Normal", and "Running Cool".

All I accomplished by questioning Goody on this and telling him these forums say NORMAL is a bit above 175F was piss him off.
 

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Discussion Starter #33
About the same as your describing at high speed, high revs. Then at 55 mph, temp was just above 175. Here is my thread on it-look at MBGrahams comments about ignition timing.

How hot does yours run?
https://r.tapatalk.com/shareLink?share_fid=13657&share_tid=2960826&url=https://www.benzworld.org/forums/showthread.php?t=2960826&share_type=t


Sent from my iPhone using Tapatalk
I can get a timing light and verify. He mentioned 27 degrees at 3000 RPM. Should both vacuum lines be connected or disconnected?
 

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Thank you for the responses.
Goody's Automotive in Scottsdale set the ignition timing as well as the air/fuel mixture. They appear to be the GO TO shop for the 450SL in Arizona, so I have to assume those factors are in check.

The condenser fins are straight and so are the radiator fins.

Motor oil is 0W40. I'll check if it coasts well to determine if there is excessive drag.

I am not an engine mechanic but I think that the issue may not be a lack of cooling but one of generating more heat that what the cooling system is meant to handle (if that makes sense). Not sure if this relevant of not, but if I open the hood when the engine is hot and running, the exhaust manifolds read mid 400's F (cylinder 4 reads mid 500's).

Goody's mentioned that 212 F was "PERFECT" and "Normal" but now that we have triple digit days in AZ I find the temp readings of 220/225 ALARMINGLY high.

I just don't want to make the mistake I made earlier of replacing good parts blindly.
Measuring temperatures with IR remotes is handy for checking radiators for cold (blocked) spots.
Drilling a few small holes through the thermostat plate was quite common for hot climates when I lived in Africa and later the Middle East.
Old Mercedes diesel hands should be familiar with it too.

Re de oiling, I used to see detergent in Porsche shops close to 50 years ago. A separate citric acid flush should be done before new cooling system parts (in contact with coolant) are installed. Otherwise, if a water pump is getting close to the end of its cycle, the citric acid flush could be the kiss of death. The bare post C A flush minimum required would be a new thermostat imo.

Anyone who ever removed the heads, has seen how full of gunk the coolant channels there and in the block are.
The blocks coolant channels end at the head.
My friend and oldtime Mercedes mechanic Jerry (RIP) told me, for hot climates the old Mercedes hands would continue the blocks coolant channels by slightly drilling into the heads.

Your coolant system was pressure tested, and held pressure. It would be interesting to know the pressure measured, and whether it was within Mercedes spec operating pressure?

The fan coupling swap to 380 sound worth a try. No self service wrecking yards in your area to get a cheap working one to try before ordering more new parts?

If radiator, water pump. thermostat, hoses (incl those behind the firewall) and clamps are good (no leaks) it shouldn't be that difficult a problem to solve.

I seem to recall a AZ or S Texas member having a higher cooling capacity radiator made at a quite reasonable price, but he installed a electric fan as well.
Cheers
 

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...
Besides, I really suspect that what I have is an engine generating more heat than it is supposed to as opposed to a malfunctioning cooling system. I would really like to identify the cause.
...
What you choose to do is your prerogative. I am confident the radiator and system (when functioning correctly as intended) is more than capable of cooling the engine at highway speed and at idle in any climate. My car sat idling at >50°C outside temp ('bout 120F) for 1.5hrs with aircon on a hot summer day being stuck at Sun City gates (South Africa) and temp needle did not venture above ~105°C (220F). As soon as we moved, the temp came below 100°C mark. Engine was running on the lean side at that time (CO was set for 1600m low air pressure altitude of Johannesburg). Fan at that time was visco-flex (full flow from about 1000rpm to approx 3500rpm, at idle provides a tiny bit more air than the thermo coupled)

If you want to pinpoint the culprit and rule out the thermostat changeover (as per my suggestion), take the old thermostat and modify it to be fully open at the front end and modify back plate to close the coolant re-circulation shut.
This should force all the coolant through the rad (and none to recirculate) and it should take forever for the engine to warm up, if it will indeed warmup.
If this is not the case than you'll have a perfect setup to chase the next bottleneck in heat dissipation.

My twopence...
Not that I was never wrong before and I may be wrong on this, the suggested route is where/how I'd tackle the issue.
 

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Discussion Starter #36
If you want to pinpoint the culprit and rule out the thermostat changeover (as per my suggestion), take the old thermostat and modify it to be fully open at the front end and modify back plate to close the coolant re-circulation shut.
This should force all the coolant through the rad (and none to recirculate) and it should take forever for the engine to warm up, if it will indeed warmup..
Would you please explain what you mean by THERMOSTAT CHANGEOVER?
 

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I'm just throwing this idea out there. While not specific to the 450SL, being that the car is 42 years old the cooling passages in the block may be a bit clogged despite the chemical flush. So it might be worth the handful of sheckles to invest in a custom, larger aluminum radiator core. In my race cars a free flow four core rad is ordered before I finish building the motor. Perhaps that investment would bring you peace of mind.
 

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Discussion Starter #38
What you choose to do is your prerogative. I am confident the radiator and system (when functioning correctly as intended) is more than capable of cooling the engine at highway speed and at idle in any climate. My car sat idling at >50°C outside temp ('bout 120F) for 1.5hrs with aircon on a hot summer day being stuck at Sun City gates (South Africa) and temp needle did not venture above ~105°C (220F). As soon as we moved, the temp came below 100°C mark. Engine was running on the lean side at that time (CO was set for 1600m low air pressure altitude of Johannesburg). Fan at that time was visco-flex (full flow from about 1000rpm to approx 3500rpm, at idle provides a tiny bit more air than the thermo coupled)

If you want to pinpoint the culprit and rule out the thermostat changeover (as per my suggestion), take the old thermostat and modify it to be fully open at the front end and modify back plate to close the coolant re-circulation shut.
This should force all the coolant through the rad (and none to recirculate) and it should take forever for the engine to warm up, if it will indeed warmup.
If this is not the case than you'll have a perfect setup to chase the next bottleneck in heat dissipation.

My twopence...
Not that I was never wrong before and I may be wrong on this, the suggested route is where/how I'd tackle the issue.

Djenka;
Please explain what a Thermostat Changeover is? Does Changeover mean REPLACEMENT?
 

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I would check to see if cooler thermostats are available for those cars. Also if the thermostat housing will seal without a stat then remove it to verify coolant circulation. Also the change of oil to 20/50w would be a good idea.
 

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Djenka;
Please explain what a Thermostat Changeover is? Does Changeover mean REPLACEMENT?
I believe what he is talking about is the duality of the thermostat. When the coolant is cold, the front of the thermostat (coolant to the rad) is closed and the rear (bypass) is open to allow re-circulation of the coolant. As the coolant heats the rear of the thermostat closes and the front (coolant to the rad) opens. Unless I am mistaken, he is referring to the point at which the rear closes and the front opens, as the changeover. :thumbsup:
 
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