Sounds like you may not have an issue at all then. Note that the aux fan low speed is triggered ONLY by refrigerant pressure. The high speed is triggered ONLY by coolant temperature (above 105C). If you see temps over 105C and the fan isn't on high, you need a new switch (the 3-prong one at the head water outlet). If temps never reach 105C, the fan doesn't need to be on.

I tought I'd add my $.02 regarding the performance of the 603 in the SDL on the hottest day of the year, to date.

Ambient: 95°F.

At 60 mph and below, the engine would maintain a temperature of about 95°C. However, as soon as the speed was increased to 75 mph, the temp climbed to about 99° and, on occasion, touched 100°C. It never rose above this value.

The a/c with R-134 did an admirable job at these temps. It could not get the cabin down to 70°F. but, it was reasonable confortable at an estimated temp of 76°F. or so. This was in direct sunshine, as well.

In some bumper to bumper traffic, the temp actually dropped to about 95°C. The a/c, however, showed its limitations. The vent temps climbed accordingly, as would be typical with this refrigerant.

I'll add to this though in a not so favorable way I guess. I recently returned from a trip to Florida in my SDL. Without the A/C going through the mountains the temp stayed around 95°. When I turned the A/C on, with the ambient temp being around 90°F and my speed at 80+, the temp went up to about 119-120! It did that if I was heavy on the accelerator going up an incline with the A/C as I said earlier, and I don't think that's right. The thing is though, once I returned from there, I haven't had any problems at all so I don't know if it jut had to do with elevation or what? When I wanted the temp to drop (like when it was nearing 120°) I could just let off the throttle and you could just about watch the needle drop with your eyes.

Now, for my diagnosis, everything passed. With the car at ~110°C and the ambient temp still around 90° I shut the car off and the fan stopped within 1-2 turns of the engine stopping so that's good. Also, with the car idling with the A/C on the aux. fan was roaring and definitely moving air. The car actually would run cooler idling under the same conditions than if the car was traveling over 80mph. 80 seemed to be the magic spot because at speeds lower than that the temp would stay around 95-100 with maybe more of an increase going over smaller hills. I wonder why the 603 seems to fair so poorly climbling elevated ground? My car seems to be more drastic than the thread starter's, but they're still very similar in many ways. What gives? The radiator is 3 years old, all fans (electrical and mechanical) are functioning as they should, the radiator is clean and was flushed with a heavy dose of Prestone flushing agent 2 months before I left. I used Zerex and actually used about a 60/40 ratio of water to coolant. I would think the 60/40 would help even more than 50/50 since I've read that the water dissipates heat better than the coolant. Anyways, thanks for reading the long post.

Thanks
David

Thanks
David

__________________
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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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My thought is that the horsepower required to maintain 80 mph and simultaneously climb a hill with a decent load in the vehicle must closely match the available horsepower: 108 hp (estimated at 3500 rpm).

There is no possible way this cooling system can handle maximum power from this engine in 90°F. ambient temperatures. In fact, I don't even think it can handle it in 80°F. temeratures. If you keep you foot in the pedal for sufficient time, it will definitely overheat. It might take 10 minutes under this load, but, it can't survive forever this way. In fact, M/B knew this because they setup the Klima to dump the compressor when the coolant temperature reached 120°C.

But, that's why they give you a temperature gauge. At 110°C. it's time to back off the pedal if you want to keep the a/c going.

the difference is subtle, but i don't think that your statement about handling max power at 90 degrees is necessarily true.

the reason that the factory built in the safeguard, i believe, is simply to guard against system failures such as a bad fan, thermostat, radiator, etc. no matter what the operating conditions are. a reduction in the power being produced is a good way to limit damage and to give the driver a graphic sign that it is time to look at the guages.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Well, there is more than enough evidence from many members, including me, that the engine will easily climb up to 110°C. under heavy loads and high ambient conditions (95°F.).

So, what is you basis to conclude that it won't reach 120°C. if the load is maintained for sufficient time?

David has already confirmed that this occurred for his vehicle.

Others have backed off the power at 110°C. to prevent the engine from reaching 120°C.

Your only basis is to conclude that all of these cooling systems are not in acceptable operating condition. On that point, I don't agree.

a hard time believing that the factory didnt supply a system that will operate correctly with full power at 90 degrees. in fact i would think that they would have tested it to operate correctly at at least 100 degrees.

i think it is not logical to think otherwise.

these cars are twenty years old. are you saying that everrthing is perfect in them? it seems a stretch to me.

i still say the cutout feature that you mention is for system malfunctions rather than a designed feature to compensate for a cooling system that won't operate correctly at 90 degrees.

if you were talking about gm not mb i might agree.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I fully know that you have a hard time with it.

And you might think that M/B would have done the proper job.

There is plenty of evidence on the forum that the engines cannot maintain maximum power for an indefinite period without getting up to 120°C. Now, if you accept that you can run at 120°C. with an aluminum head and not get into a problem, then, I can't be certain that it will climb above this value.
But, it will surely get there.

Are all the cooling systems brand new? Of course not. But, what's the average degradation in performance? Maybe 15%? So, the cooling systems that are marginal will simply get to the limit faster than the one's that are not.

Just about everyone has easily seen 100-105°C. temperatures without too much effort. All it takes is a hot day and a heavy load. Getting to 120°C. is certainly more difficult, but, I'm fairly convinced that most of them will get there, given sufficient time.

Remember, that your premise by M/B is probably true. They probably figured that the longest possible stretch at maximum power would be 15 minutes. If they could get the engine to make it for 15 minutes, then they would be all set. Who would have one of these engines running at maximum power for more than 15 minutes? It's almost impossible.

I'm saying that the engine cannot stay below 120°C. if you ran it at maximum continuous power for 30 minutes.

Before changing any more parts, or assuming the worst, buy or borrow a laser temperature probe, and measure the coolant/engine temperature yourself. Alternatively, have a garage with one of these things do it for you.

This will determine if your coolant temperature gauge is accurate or not. It may turn out to be an inaccurate coolant temperature gauge. Has happened many, many times before.

Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]

If you have trouble believing, than why did MB redesign their heads for these engines several times? The whole reason, or subject, for this thread is staying out of the overheat danger zone for the weak and fragile, highly prone to crack, and poorly designed 603 #14 aluminum head! MB did screw up!

Getting up towards 120c for the redesigned #22 head is probably not an issue, although I doubt anyone here would want to test to see, but is supposed be able to sustain higher temps longer without cracking rendering this issue all here are talking about, moot!

The head redesign has NOTHING to do with the cooling system. It was a flawed casting, they adjusted it several times. End of story.

About the cooling problems, David, I think you have something wrong with your car. I would strongly suspect the radiator, assuming your thermostat is OE and fairly new, and you have a good radiator cap. Someone else had similar problems recently with an 18 month old radiator, and installing a new one cured it. Don't think that a 3-year old radiator is "good". I assumed that when I bought my car in 1997 with a 4-year old radiator and I was seeing temps of 110-115C in the summer. A new radiator cured that.

FWIW, after I replaced the radiator, I could climb I-80 to Reno up steep grades with my foot to the floor (near full power) with the A/C on in approx 95F ambients and my temp would NOT go over 100°C. I think that kind of poo-poo's the theory you guys are coming up with about inadequate cooling capacity. When new, or functioning as new, there is NOT a problem with the 124/603 cooling. However they seem to be very prone to plugging up the radiators internally (the core turbulator fins probably catch more crud than they improve cooling ) and that's my theory why the radiators may need replacement.

Note in this factory PDF document that "high temps" are considered to be over 110°C, and that the solution (after ruling out other causes) is to do a citric acid flush with the OLD radiator in place (to catch the crud), then replace the radiator!

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Dave
Boise, ID
Check out my website photos, documents, and movies!

Well, Dave, it's certainly possible that the radiator is the culprit, but this one has a "relatively" new radiator and it has no problem climbing up to 105°C. under heavy load for about six minutes.

I wonder how much the radiators degrade with time. Would most radiators that are older than five years of age degrade to the point where "inadequate cooling" becomes apparent?

One other question regarding your test: Did the temp stabilize at 100°? Did this test continue for a long enough period to ensure that the temp. was not climbing? Maybe the hill ended before the temp. stabilized??

I will second this statement. I do this drive 4-5 times a summer and, with my ORIGINAL radiator, my temp is always at or slightly below 100°C. The last two times have been with the ambient temps well into the 100s.

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Chris

'04 ML500 - 53k, Inspiration Edition, Desert Silver
'11 Audi A4 Avant - Brilliant Black
'87 300SDL sold
'99 C280 Sport sold
'85 190E 2.3 sold

Up to 105°C after extended full load is normal, IMO. However I stil think 115°C or more (except under highly unusual conditions!) indicates a problem that needs fixing.

About radiator degradation, I haven't been able to determine a cause. Some people (like Chris) have original radiators working fine, others have radiators that require replacement in 1.5-5.0 years, well short of a normal/expected life span. I believe it's due to deposits internally but don't have a clue as to why that happens or where the deposits come from.

As to the hill climb up I-80, it's usually 3-6 minutes at a time... enough for temps to mostly stabilize. The only place I know of that's more of a torture test is the Grapevine.

Brian, did you catch my recent thread about A/C performance on the email list? What are your minimum vent temps in the morning before it gets hot out? If not in the low 40's, adding the resistor shunt to the ETS (evap temp sensor) may help drastically. I just did this to my 300E with R-12 and it dropped vent temps from low 50's to high 30's!!! Talk about a major improvement...