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380 SL 1983
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Discussion Starter #1
1983 380SL just back from garage. Mechanic wants $3000.00 to replace head gaskets. He explained engine heats up during idel which is his indication hot exhaust is entering the cooling system. I had radiator flushed and new themostat put in.

HOw hot should the engine run? Is there anyway I can determine if it is a leaking head gasket?

All help is greatly appreciated.
 

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jkoch said:
He explained engine heats up during idel which is his indication hot exhaust is entering the cooling system.
If this is what he told you - this exact explanation - then he's an idiot. Find another mechanic. Coolant leaking and contaminating the oil would be a problem. Coolant leaking into the cylinders and leading to low coolant levels would be a problem. Oil leaking into the coolant and sludging up your cooling system would be a problem. Exhaust gases radically heating up your coolant and leading to overheating isn't an issue.

My engine idles just above 175F on a cool day. If it's a warm day it might get up as high as 200. If I've been driving it quite a bit and I stop for a long idle, it might go above 212 unless I drop it into neutral and let the engine rev a bit higher.
 

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380 SL 1983
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Discussion Starter #3
Thank you.

One thought is I have never heard the front aux fan kick on. The AC was unhooked by prievious owner which may have made this fan inoperable, but not sure.

Can I test and if it is not operating should i be concerned?
 

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jkoch said:
1983 380SL just back from garage. Mechanic wants $3000.00 to replace head gaskets. He explained engine heats up during idel which is his indication hot exhaust is entering the cooling system. I had radiator flushed and new themostat put in.

HOw hot should the engine run? Is there anyway I can determine if it is a leaking head gasket?

All help is greatly appreciated.

You ask 'how hot should the engine run?', I ask, how hot DOES it run? Give us some parameters.

Did the mechanic check the coolant for the presence of combustion gases? It's a rather simple test and a standard check when head gasket integrity is in question. Doesn't speak well to his thoroughness. Dave
 

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380 SL 1983
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Discussion Starter #5
It tends to run up to 100C during idle and slow traffic. I like our idea on checking coolant for combustion gases. Is there a place I can send a sample to?

I am still wondering if the aux fan should be running at times? How do I test the aux fan and could this be part of the issue?

Thank for your help in advance!
 

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'80 450SLC Afro RHD Ikonengold
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jkoch said:
It tends to run up to 100C during idle and slow traffic.

Thats the way, aha, aha, you don't like it.
105°C in slow traffic and on hot day is normal but not a celsius above!
 

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1959 220S cabriolet, 1983 240D original owner, 1999 E300 turbo diesel, 1988 560SL, 2003 SLK320
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Mine is pretty much rock solid at about 85° under all conditions.

Len
 

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Outstanding Contributor , Bob's Your Uncle!
-----'83 280 SL----- 5 speed....The PIG
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sokoloff said:
Mine is pretty much rock solid at about 85° under all conditions.

Len
Mine too...but I have the much desirable six banger.
 

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Djenka018 said:
Thats the way, aha, aha, you don't like it.
105°C in slow traffic and on hot day is normal but not a celsius above!
And make sure your coolant is the correct type and ratio.
 

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jkoch said:
Thank you.

One thought is I have never heard the front aux fan kick on. The AC was unhooked by prievious owner which may have made this fan inoperable, but not sure.

Can I test and if it is not operating should i be concerned?
I read in another post recently that the aux fan engages standard at 80c, and a 100c (relay?) was available. (Don't quote me on this.) You should be able to test the fan like dugalds horn. Disconnect the aux. fan wiring and apply 12VDC to the electrical connectors. Watch your - & + or the fan might turn backwards.
Good luck.
 

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jkoch said:
It tends to run up to 100C during idle and slow traffic.
At what ambient temperature? What is the operating temp on an open road? And what was the original complaint?

jkoch said:
I like our idea on checking coolant for combustion gases. Is there a place I can send a sample to?
Any well equipped repair shop should be able to check that. Are you 'losing' coolant but have no apparent leaks? Do you seem to have excessive pressure in the radiator?

jkoch said:
How do I test the aux fan and could this be part of the issue?
The fan motor itself can be tested with a 12V supply and a ground. There is a fan wire disconnect plug on the right hand side of the radiator. As to what may have been removed or disconnected by the PO that's time for a pro.
 

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Discussion Starter #12
Ambient temperature varies with same results but have seen issues s low as 65F.
I do not believe I am losing coolant.

How do I determine if there is excessive pressure in the Radiator?

Thanks again for your help.
 

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jkoch said:
Ambient temperature varies with same results but have seen issues s low as 65F.
I do not believe I am losing coolant.

How do I determine if there is excessive pressure in the Radiator?

Thanks again for your help.
200F+ operating temps at 65F ambient means something is not right. My SLC will stay at 175F until the ambient passes 90F.

Combustion gases leaking into the cooling system can raise system pressure while the engine is running, causing coolant overflow, while the gauge may still show a 'normal' temp.

I would suggest you locate a repair shop that will perform a comprehensive cooling system check. This would include a system pressure test and gases in the coolant.
 

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Djenka018 said:


Thats the way, aha, aha, you don't like it.
105°C in slow traffic and on hot day is normal but not a celsius above!
This is correct. But on A/C cars Mercedes says it's even OK for them to approach the red zone.

So stop worrying, and put your wallet back in your pocket. :)
 

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page62 said:
This is correct. But on A/C cars Mercedes says it's even OK for them to approach the red zone.

So stop worrying, and put your wallet back in your pocket. :)
I'd like to see that part of manual my self too for more confidence as once, on a extra hot day and 2hrs in stopped traffic, I had mine approach red but it never entered red it self.
Just did not like it and I feel if there is money in the wallet, it would not feel sorry to spend it on aux fan
 

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There's an MB factory service bulletin floating around out there somewhere. Like the great urban legends, I've read its contents at one point or another...but I don't have it on hand.

This "running hot" thing is one of the great obesessions that R107 and C3 Corvette (68-82) owners have in common. We're always trying to fix a problem...that doesn't exist!!!
 

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ears said:
I see quite a few posts about the W107 running "too hot". Often times, it seems the reports are of the engine running above 100C at times, etc, etc. Also, I often see the results best described as the "shot-gun approach" when it comes to diagnosis, ie replace this, replace that, etc.

First, let me suggest it be determined IF overheating is actually occurring at all. The W107, and many other MB engines are designed to run "hot" compared to what us USA folk are used to from Detroit/Japan. It is not uncommon for these engines to run close to the 100C mark, with occasional excursions above also common. Anecdotally, this seems "hot" when compared to the iron I'm used to, but it is normal and by design. If the excursions above 100 are frequent, and near/into the red, then you have cause for concern. While its true a 560Sl has an 80C thermostat, it is not fully open until 94C. Realizing this, its easy to see how the gauge in the dash could rise above 100 while the thermostat is reacting, assuming the two react equally for a given temperature, and hover near 100 during normal operation.

If an engine is overheating (really, to be accurate, we should say the coolant temperature is above design criteria), the obvious question is WHY? Really, there are only two reasons... Either the engine/tranny is generating too much heat for the cooling system, or the cooling system is not functioning adequately. Often, the assumption (and more often than not, correctly), is that the cooling system is "faulty"; however, this may not always be the case. One should consider the state of tune of the engine among the lists of items to check. An engine that is out of optimum tune, ie running very lean, or otherwise compromised will be guilty of generating more heat than the cooling system was originally designed to accomodate. The engine timing is also critically important to the state of tune, and the heat thereby generated. The tranny's health must also be brought into the fray as it can contribute directly and indirectly to cooling system inadequacies: directly by tranny fluid running above normal, transferring heat directly to the cooling fluid, and indirectly by inducing strain on the engine if not coupling/shifting correctly. Given that we are considering vehicles around 18-30 years of age, there may be more heat in the system than originally designed due to mechanical weakness in the drivetrain. Another list of things to consider can be called extraneous causes and can be related to dragging brakes, missing/mal-adjusted fan shrouds, tire aspect ratio and inflation, ratio of antifreeze/water, etc. Even the type and grade of oil can contribute to an engine producing higher levels of heat than originally designed.

If one accepts the above postulates, then it becomes incumbent upon the examiner to consider many factors aside from only the cooling system parts, ie clutch fan, thermostat, radiator, etc. In reality, for equipment of the age and mileage we are concerned with here, the cause will likely be a combination of these factors. The holistic approach must therefore be utilized in ascertaining a solution.

I suggest the following:
1. reSEARCH to determine what "normal" should be (expect a range).

2. Test to be certain overheating of the cooling fluid is actually happening. By test, I mean, utilize measurement devices beyond the gauge in the dash.

3. Check for extraneous causes. Focus on anything that has been changed recently, or serviced, etc.

4. Examine the systems, heat generating (engine/drivetrain) and heat exchanging (cooling system).

Somewhere within, the answer lies...


Author's note: The opinions expressed here are belonging to the author, and have been developed from years of mechanical experience with engines from motorcycles to freight locomotives and are by no means all inclusive or solely limited to the items mentioned.
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RM Smith
Here is an old post by ears that hit the nail on the head
 

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Thanks for digging that up... I forgot about that post :)
 

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Discussion Starter #19
Ears said:
Thanks for digging that up... I forgot about that post :)
Back from Shop with new thermostat (90degree) and flush.

WORSE: Cools fine driving down road, running around 95 - 100 C. BUT idling the temp shoots up immediatley to red zone. Even as slow speeds like 30mph it stays around the 100C mark.

Clutch fan? how do i check?

Any suggestions are greatly appreciated.

Thanks,
 

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Someone can probably describe this better than me...

When your car is cool, your fan should freewheel somewhat when you give it a push with your hand. When it's warm, there should be some resistance to movement when you do this. If it's still freewheeling, you have a problem.
 
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