Swogee,

If your engine doesn't overheat to the point of boiling and loosing coolant, you have no problem. Notice where the red mark is on the temperature gage. As long as you stay below the red mark, your engine is not overheating.

P E H

Guys, let's differentiate between overheating/dangerous temps, and "normal". No, 110C isn't dangerous (assuming the system is holding 1.4 bar pressure like it should with a new cap). Is it normal? No, not even under heavy load. My car is the same as LRG's. I can climb a steep grade to Reno in 95F ambients, AC on max, luggage in the trunk, with my foot near the floor (75-80mph and accellerating), and the temp will stay at or below 100C on the gauge. That's with a good radiator, t-stat, fan clutch, new head, yadda yadda. Regular trips to 110C - outside of Death Valley in August - are NOT NORMAL.

And *please* don't anyone quote some idiot dealer, mechanic, or zone rep who chants the "go away" mantra of "If it's not in the red, it's perfectly normal." I went through that crap back in 1998 after I bought my 1987 300D and it was running at 110-115C all summer in Sacramento (100-110F ambient temps). They all said it was "normal" and I should ignore it. Funny thing was after I replaced the radiator (and fan clutch), under the SAME conditions (100-110F ambients), the car would NOT even touch 100C!!! Blithering idiots, all of them, who don't want to deal with a problem until it becomes a disaster (in the red zone). The only reason I pursued it was a sharp dealer parts counter guy who had the same year/model, who had recently installed a new radiator in his, and he looked at me like I was nuts when I said mine ran at 110-115C... and I looked at him like HE was nuts when he said his ran at 95C all summer! :p :p

Wouldn't hurt to replace the gauge temp sender in the head (below the #2 injector, approximately)... usually they read *low* when they fail, not high, but a new one is only $10 and IMO it's good preventive maintenance on a ~20 year old car...

I second GSXR's opinion. After having just spent nearly $3000 all together to replace the head on my 87 SDL, I would recommend being overly sensitive to any temperatures above normal with a 603 engine with a "14" head.

__________________
Keep everything as simple as possible-but no simpler--Albert Einstein

With these cars, is it not true that defrost only releases heat and does not engage the A/C compressor? I have not checked this lately, but this was a difficult adjustment compared to other species of cars. The Hi/Lo setting would be used to remove humidity (defrost) in the summer.

At least this is how my 3 work.

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Alan Hamm
'87 300SDL 277K Miles
'89 560 SL 68K Miles

Thanks for all of the posts so far. I have read them, and I have a few responses.

1) The overheating problem was occuring prior to the replacement of the radiator. The old radiator was leaking out of the driver side tank, so I thought (and a mechanic that I took the 300TDT thought) that a new radiator would fix the problem. I guess we were wrong.

2) I didn't think about the fact that turning on the defroster would click the A/C on as well. On my Passat, the A/C compressor turns on when I turn on the defroster, however on the 300TDT it is a moot point since the A/C doesn't work due to a lack of R-12 in the system. I have turned the heater on as well to reduce the temperature of the engine and it pretty much has the same effect as using the defroster.

3) I have not had the thermostat replaced, and that will be done by tomorrow.

4) The radiator cap is a "Stant" brand 20 psi cap. The mechanic checked the cap and it held 24 psi no problems. I don't think it is the cap, but I will replace the cap when I order some more parts.

5) The fan is the original aluminum unit. It could be causing the problem, so I will have to check it out. The engine only heats up during the hill climb, which is actually about 2.5 miles long. As soon as I turn around and go down the hill the temp drops to normal.

6) The water pump is also a possibility. I am pondering if on changing that out next. I suspect it will cost a lot to have a mechanic do it so I will most likely do that myself along with the fan/clutch, belt tensioner, and belt. I am also planning on replacing the temp. sender when I pull the intake manifold off.

7) I may be overly concerned about a temperature of 110C when the 300TDT climbs hills, but after reading about all the cracked original heads with a "14" casting number I think I am justified since my head is original. The main thing that worries me is that if the car heats up with the outside temp only 85F, I wonder how hot it will get if the outside temp is 105F or if the A/C is actually turned on and functioning properly.

Side note: There is only anecodotal evidence that the Passat temp gauge is an "idiot" gauge. I have heard this story before, and I am not entirely convinced it is true. I have seen the gauge lower than 190 as the Passat was warming up. My Honda definitely has a regular temp. gauge since it moves up and down when I go over hills and into a hot areas, etc.

Thanks again for all of the responses. Keep the good ideas coming. I will keep everyone informed of what I find.


-Steve

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1987 300TDT smoke silver w/ burgundy leather interior
2000 VW Passat wagon indigo blue w/ beige leather interior
1985 Mustang SVO
1970 Chevrolet K10 fleetside, shortbed

Based on your post above, Steve, my #1 suspect is the fan clutch. Can't wait to hear what you find out...

Interesting that Dave pointed out that temp guage senders read on the low side when worn out.

This morning while getting coffee, I left the car running, A/C on, and when I came out 3 min later, the aux elec fan was on yet when I looked at the temp guage it read only halfway between 80c and the next bar line up which I assume is 100c since it is not numbered?

The last time I saw that fan come on by it's self, the temp gauge showed slightly above that 100c line!

Time to install a new sender!

Also, I should note that my temp guage runs normally between 80c and 90c + or - a few degrees.

Some quick notes:

1) Yes, the line between 80 and 120 is indeed 100C.

2) The electric fan has TWO speeds. Low speed is triggered only by A/C refrigerant pressure - when it exceeds a certain amount, a switch at the drier (either green or red) closes and turns the fan on low speed. You can short the wires together to test fan operation. (If you ever open up the AC system, swap the old green switch for a new red one, which triggers at a lower pressure and improves AC performance at low vehicle speeds.)

3) The electric fan high speed is only triggered by the 3-prong sender up at the water outlet on the cylinder head, near the upper radiator hose. The 603.960 switch is blue and rated 128/105, and costs about twice as much as the 603.961 switch (which is gray and rated 120/105). If you replace it, get the cheaper switch, which will also engage the AC safety shutoff at 120C instead of 128C, which IMO is ridiculously high.

4) The usual symptom of a bad gauge sender is plenty of heat in the winter, but the gauge showing 60-70C. It's harder to tell in summertime unless you know the t-stat is good and it still reads below 80C.

5) To explain #3... the 603.960 engine was used in the W124 in 1987, the 603.961 engine was used in the W126 in 1986-87. They are 99% identical, at least to date I have not been able to determine what the difference is between them...!

Dave, the SDL has a radiator that is very new (installed by the PO). It makes regular excursions up to 100C. on a maximum power grade for 45 seconds, no matter what the ambient temp. is.

So, based upon your comments, the likelihood is that the viscous coupling for the fan is not coupled at high temps.

Two questions:

1) At what temp should it be fully coupled?

2) Can any repair be done to the clutch, similar to the addition of fluid like the 617, or must it simply be replaced?

gsxr,
I am curious why you think it's the fan or the fan clutch when he said the overheating occurs at 75MPH, a speed at which the fan would be useless.

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Brian
87 300Dturbo 180K #14 head still running R-12 SOLD 12/2017
02 F350 Powerstroke 180K
05 Chevy Express 1 ton w/Royal Utility box 120K
08 Infiniti FX-35 40K
15 Golf Sportwagen TDI 35K
10 Sprinter 3500 chassis with a Class A Winnebago on it. 56K

Brian 1,

1) The coupling temp for the original 603 clutch with metal fan is described in the FSM. Basically, it should couple by about 90C coolant temp, but *definitely* by 100C. Make sure the airflow path directly in front of the clutch is clear or it won't couple! Bad radiators can have a small cold spot which can cause a similar problem, you can tell that by feel though.

2) You can refill the original 603 clutch with silicone fluid - there are posts detailing this elsewhere on the forum. If you have the newer, replacement 606 clutch with the plastic fan, it's risky to refill (may bend/damage the bimetal spring) and also needs lighter weight silicone fluid. Someone posted their results with this - OldSouth, maybe?


Brian 2,

It's a common misconception that the fan does little or nothing at freeway speeds. Believe me, that is FALSE! It does a lot more than you think. If it's not coupled, it's just floating along and not pulling much air. Under heavy load the clutch must be coupled, even at high freeway speeds, or you won't get adequate airflow.

Hey guys, can't help but notice, I think I just killed 2 birds with one stone.

First off, late at night, 69 degrees outside, why not do some 0-60 runs?
1 - 13.6
2 - 10.9 slight downhill (maybe 1% ?)
3 - 12.7

After the runs, the temp gauge went to the 100 mark where it was in the middle of the 80 and 100 before. I understand that the engine is under heavy load but is it suppost to heat up that fast? The first run was held as i merged onto the freeway, a good 5-7 miles later, i did the 2 other runs back to back.


As for the overheating issue, I recall last year when i had a aluminum Nissens radiator and was driving around in Riverside (inland area) with the eng. temp smack in the middle between 80 and 100 and outside temps in the 90s-100s.
After a little incident with a trench, I bought a rebuilt Behr copper radiator and notice that 80-90 temps on a freeway commute can bring the eng. temp a lil north of 100. Aside from being stop and go traffic, which i've done before also, can the temps really fluxuate that much because its a copper radiator?


And I too, still have the original metal fan and probably clutch also.

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Jason

00 Subaru Legacy (fun wagon)
96 Nissan Sentra (disavowed)
82 300SD (garage queen, will run again hopefully)
87 300DT (Gone: 10/15/2010)

Last winter I went skiiing in West Virginia and with 0 degree outside temperature outside and the wind howling, my SDL still approached 100 degrees when climbing long steep grades. On downhill portions it would drop to below "normal" because it was so cold outside. "Normal" for me is 85-90 degrees.

Regular driving in hot, humid DC weather my gauge climbs to just under 100 degress in stop and go traffic.

I spent a really long time chasing what I thought was an overheating problem in my 300D. Replaced radiator, water pump, several thermostats etc. Then I did the smart thing. Let my son drive it and bought an SDL.

__________________
Alan Hamm
'87 300SDL 277K Miles
'89 560 SL 68K Miles

Please read my former reply...

Reading all those replies, I realised I had forgotten to mention some important details.
When talking about steep mountain roads in the French Pyrénées that means really steep. These roads climb from 7 untill 15% and even more on the inside of the sharp turns (allready touched the road with the rear under of my TD).
Worse yet, these roads are very narrow and turn follows after turn not leaving 20 yards straight. So the maximum speed in all safety is about 20 miles per hour (really the maximum). That gives allmost 3000 revs in second gear without any cooling by speed. Even with the A/C cut out, they will run hot al those 300D's, TD's, SDL's, 603's and 606's. Even with aux fan in perfect working order.
Once going downhill, it cools down in a minut or less to 85° C...
In normal everyday use there are no problems at all.
So I should say not to fast with all those replacements...
Keep it cool,

Danny

That's definitely normal. Remember that the t-stat doesn't fully open until about 94C! It's temps of 110C+ that are not normal, unless conditions are very extreme, like the low-speed 15% grade mentioned by Danny, etc. I think most of the people here are talking about relatively low grades on USA highways, 6-8%, at 65-75mph... and in those conditions the temps should 'normally' stay under 105C even with the AC on.

Here's a MB service doc (PDF file) discussing 'high coolant temps', which is defined as 110C+...
http://www.meimann.com/docs/mercedes/OM603_high_temps.pdf
(note that the test is for a cold spot in front of the fan clutch.)