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Old 08-26-2001, 05:41 PM
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Help 87300E Automatic Teperature Control Problems

Hi --

I just bought an 87300E with about 110K miles on it. I love the car and love reading the posts at this site. Also in an attempt to save funds I purchase most of my parts through Phil at Fastlane.

I would really appreciate any help you could give me with the following problem. When I set the pushbutton controler cabin temperature gauge to 70 degrees when it's 90 degrees outside I experice the following problems.
1. Sometimes everything works fine;
2. Sometimes when starting the car the system pumps cold air out of the center vents and heated air out of the side vents. (To fix this I have to set the temperature wheel to "min." and the system will eventually pump cold air out of all vents but will not maintain a temp. its works all A/C all the time or no A/C); and
3. Sometimes the system works fine and then, when a system change is required to maintain a set temperature, it will start pumping heated air out of the side vents and cold air out of the center vents.
After speaking to my mechanic he suggested that I check the internal cabin temperature sensor (I replaced it with a new one) and that I check the auxillary fan that pulls cabin air over the internal temperature sensor in the headliner courtesy light assembly. I did this -- all hoses were connected and the auxillary fan worked to pull a small amount of air over the sensor. I do not know if the fan works all the time, but it did when I checked it.
After replacing the sensor the system seemed to work a little better -- sometimes perfectly and pumping hot air out of the side vents a little less frequently. But the system still suffers from the same problem, just not as often.
Does this require that I purchase and install a new pushbutton controler unit? If so, can I safely purchase a rebuilt one from the "German Star" (as advertised in the Star) for $209? or should I buy a new one? or is there a less expensive solution to this problem?
I'm pretty handy but, I am no expert. I have successfully replaced the cruise contol amplifier; the rebuilt speedometer; and the fuel level sender myself. My mechanic has done the following: Replaced the overload protection relay; the fuel pump relay; the oxygen sensor; and the struts (Bilstein HD's are great); he has rebuilt the altenator; replaced the brake pads; changed all the fluids; replaced the rubber part of the brake lines; replaced the tranny hoses, the coolant hoses and replaced the rear differential bushings and the flex discs. I also had all the broken wires between the body and the driver's side rear door repaired.
Other than the A/C problem the car seems to eat/loose a lot of oil. It could be a head gasket or a stem seal problem. Or it could be from my using a thin synthetic oil [10w30]; I've now switched to 15w50 Mobile One. Any thoughts?

Thanks in advance for any help you can give me.
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Old 08-26-2001, 08:21 PM
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It had better be a Beauty

Brother of The Benz,MMCoupey
You must have found a beauty to have done so much to her.
With only 110,000 miles showing, she require repairs that mine has just required and some mine has yet to need.
Your Automatic Climate Control is a very complex system. There isn't anything you can't do if you have the talent.
In reading your problems, the foremost items that come too mind are the vaccum elements; there are six of them, mabe seven I can't recall. They are the controllers of all of the various doors/flaps in the evaporator case.
I am the original owner of my 1987 W124030 with 179,500 miles had the Automatic Climate Control rebuilt past June.
I had all of the vac elements, expansion valve, evaporator core, blower motor assembly, all the inside seals renewed, compressor/clutch, drier reciever replaced and converted to R-134A.
As I said opening this thread, It better be a beauty, for to have the A/C rebuilt as I, if you had a $4,000.00 dollar bill, you would need a few extra bucks.
This was the first time for any service other than freon and hoses performed.
When you have to go into the dash of your Benz, be sure you replace everything as it is so labor intensive to have to open it up again.
Whiether you buy rebuilt or new, let your conscience be your guide.
As too the oil problem, do some tests to determine why.
Mine uses a quart between 1500 and 2000 miles on Mobil I.
I would suggest you aquire a set of Mercedes Benz Manuals or the newer CD. Steer clear of the Clymer and Haynes Junk.
Happy Trails Beep Beep from The Spiderman in Houston!!!

Last edited by dlswnfrd; 08-26-2001 at 08:30 PM.
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Old 08-26-2001, 09:05 PM
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Location: Evansville WI
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On a mono-valve (no seperate passenger and drivers side control) system like yours, it really sounds alot like the push button panel is going bad. The solder joints start to fail and cause intermittent problems like this. A bad vacuum element complaint is usually about one outlet not working at all.
You could try to save money and get a reman push button panel. I am unaware how much new ones are going for now, but a new one would be less of a "?" as far as the durability of the unit. Typically MB won't offer a particular item as a reman unit if rebuild isn't very feasable or the durability of a reman is questionable. I have replaced several push button panel in the shop that had "remanned by:" stickers on them, of course I have replaced many more original units, but the point is I don't believe the reman units were nearly as old as the original units I have replaced. It's a gamble is the long and short of it, but if it is junk immediately I am sure it is guaranteed at least for a while. The MB part I believe is guaranteed for 1 year/unlimited mileage.
The oil burning problem I really doubt is the head gasket. Usually the first sign of a blown head gasket is either external oil leakage or the introduction of oil into the coolant, so be alert for these developments. Could be the oil you're using. Do you see any signs of blueish exhaust smoke? At this mileage, valve stem seals are a distinct possibility. Usually when this is happening, you have cold start problems, what is usually described as a "false start". It seems like it started, but you stop cranking and it stalls right away, then starts OK on the second attempt. Pulling the spark plugs usually shows not an oily deposit, just kind of a normal-looking deposit, but rather heavy-kind of a grayish or yellowish looking deposit. If you think you are leaking the oil out, then check the front cylinder head cover "lip" seal, you will see oil on the right side of the engine, starting at the front between the head and block.
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Old 08-28-2001, 12:50 PM
Posts: n/a
Update on A/C & Oil troubles

Dear Spiderman and Gilly:

Thank-you very much for your help and replies. I will try to answer some of your questions and more fully describe my oil usage problem. I hope that you will be able to tell me whether its the head gasket, the valve stem seals or that my oil usage is normal.

Yes the car is a beauty, with a perfect interior and exterior (I bought it from the owner of an autobody shop, and know some of the guys who work for him). And I forgot to mention, I had the A/C compressor, suction hose, expansion valve and receiver dryer replaced (about $2,800 using parts from fast lane). A mechanic ex-friend of mine blew the system up when converting to 134a without knowing that 134a is under one third more pressure than freon. So when he filled the system to the pressure recommended for freon the system blew. The only other unecessary money I blew on the car was the custom installation of my MBQuart/Alpine head & CD Changer system -- the sound system is amazing.

In any case, re: the A/C problem, what I will do is purchase a new or rebuilt (haven't decided which yet) pushbutton controler unit and install it. I would appreciate any help on removing the old one and installing the new. I don't think my a/c problem is vacum or valve related -- the right vents work when directed to -- the only problem is heated air coming out of the side vents when is should be a/c.

Re: oil usage. I drive the 87 300E really hard, only use synthetic (15W50 Mobile One now) and go through about 1 quart for every 2,000 miles I drive when using 10W30 synthetic. Reading the posts this seems to be normal usage. Is it? Also, with synthetic can one safely go 5,000 to 7,000 between changes?

My mechanic saw something that looked like oil in the expansion tank -- but nobody was sure where this came from. The previous owner or some previous mechanic may have put a leak sealer in there. In any case the mechanic did a "blow-by" test and said that the results were negative (i.e.: no oil leaking into coolant). The plugs looked fine, and no bluish smoke was seen coming from the exhaust. We then concluded that replacing the valve cover gasket and the cam cover gasket would eliminate my oil use. It did not. I cleaned the engine and found only very little seepage out of the crank case cover gasket, and some fresh oil on the oil pan (but once cleaned off, it did not reappear).

Today the mechanic is replacing the water pump (it just started leaking like mad) will flush the system and perform another blow by test.

Please let me know whatever you can -- at this point I'm a little mistrustful of my mechanic and am afraid that he is trying to suck me into an unecessary head gasket job.

Last edited by MMCoupey; 08-28-2001 at 01:00 PM.
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Old 08-28-2001, 11:06 PM
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That's not a great amount of oil loss, given 110K miles. Sounds like a typical amount for an engine with that amount of miles, plus maybe worn valve stem seals, so I would investigate that end of it. I would find out how long the previous owner had it and if he either had valve stem seals done, or a head gasket replaced. I would be a little concerned about traces of oil in the coolant, but if the previous owner had a head gasket blow out and then fixed it, I wouldn't be as concerned. There is a coolant overflow tank in the right fender that often doesn't get changed when it's contaminated by a head gasket failure. If it doesn't get replaced, it can cause continued coolant contamination after the gasket is fixed. Actually, many times the pressure tank isn't even replaced, although it should be, as cleaning it doesn't work very well, and it isn't extremely expensive, I usually recommend replacing both the pressure tank and the overflow container if the coolant has oil in it.
As I said before, the usual sign of valve stem seal wear is a "false cold start" complaint, deposits on the spark plugs, and also a slight oil consumption problem such as this.
I would say you are good to run the synthetic oil out to about 6 to 7000 miles between changes no problem.
Don't be too surprised if the mechanic recommends the belt tightener for the fan belt, this is quite common when doing the waterpump.
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Old 08-29-2001, 12:04 PM
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Join Date: Apr 2000
Location: Falls Church, VA
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Since there seems to be no shortage of funds, you might alos want to do the fan bearing/housing while the belt is off (if it has not been done).
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 08-29-2001, 12:21 PM
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Update on A/C & Oil Troubles

Dear Gilly:

Thanks for your reply. Re: the A/C problem I replaced the push button control unit with a reman from Phil ($178) compared with $400 new from MB. That did the trick. The system seems to work fine now (knock on woood), and maintains what ever temperature I set the temp wheel to.

Re: Oil -- my mechanic just replaced the waterpump and overflow hose -- he did not replace the overflow tank but he did clean it out well. He said that he did not find oil in the coolant hoses and that I should bring the car back in two weeks to see how much oil if any leaks into the overflow tank. With the blow by test coming out negative two months ago, I tend to agree with you that the oil may have gotten into the system when the previous owner serviced the car.

If one liter per 2000 miles is not alot then I think valve stem seals. The car does expreience false starts every so often. About 1 false start in 40 starts since the alternator has been rebuilt. Before that it experienced 1 false start in 10 -- mostly when it was cold.

But despite all this the mechanic seems convinced that it is a head gasket problem; so much so that he did not do another blow by test after replacing the water pump. I'll monitor my oil usage to see if it goes down since changing to 15W50Mobile1.

What a heart ache -- this old car has already cost me 50% more than what I estimated the car would cost. Original estimate: $12,000 with purchase and restoration; Current estimate: about $18,000 if I get the head redone; currently, however, I've dropped about $15,000 on the car.

Despite all of this -- the thing is great, a pleasure to drive -- runs perfectly and quitely with the original exhaust -- and I doubt I will ever get rid of it. I will simply buy a new or newer MB and keep the old 300E as a station car, etc. (The interior looks brand new, perfect beige MBTex, and I replaced the consol wood and the astray surround wood (about $150).

Thanks again for your help and any other advice that you think may be useful to me.
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Old 08-29-2001, 12:44 PM
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As a quick aside to this thread, where exactly is the overflow tank located? I recall Donald describing it being behind the front passenger side wheel well inspection panel. I saw about 8-10 screws in the entire wheel well -- do i need to remove all of those to gain access to the tank?

Reason I ask is I recently had ATF in my coolant and have yet to clean the expansion tank out. I'm still getting traces of oil in coolant after doing a *thorough* de-grease flush of the coolant system and believe that bugger tank is the culprit.

Thanks for any info you might have!


'91 300E 198k
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Old 08-29-2001, 09:21 PM
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Paul and especially Marc:
The overflow tank is located in the right fender behind the wheel. Yes, the inner fender trim is removed to get to it.
Marc, you or your mechanic keep referring to the pressure tank as the overflow tank. It's important to keep this straight. The part you can see under the hood is the pressure tank, it has a pressure cap (or under common terms is referred to as a "radiator" cap). Under the pressure cap is a fabric wrapped hose which attaches to a nipple on the filler neck of the pressure tank, kind of leads off into la-la land, looks like it probably leads to the ground eventually, right? Nope. THAT hose is going to the "overflow" tank, the one everyone forgets about, out of sight, out of mind.
If you get a bad case of blown head gasket, you can get quite a bit of oil into the cooling system. The extra oil fouled coolant will eventually make it into BOTH tanks. If the problem is fixed with the head gasket and everything cleaned up and the PRESSURE tank cleaned or hopefully replaced, but no one removes and cleans or replaces the "overflow" tank, then the cruddy oil will eventually be introduced into your nice, clean cooling system through the normal way of the coolant contraction during cool-down periods, as it is intended to work.
Marc, I am not suggesting that the oil got into the cooling system through any normal "servicing", maybe this is just a mis-statement. I would be more curious if the head gasket had failed and was repaired, or even more curious if the previous owner also felt that the head gasket repair was imminent and he bailed on the car. If it were mine I think I would REPLACE the pressure tank, it is too complex inside to do any real good cleaning, and remove and pressure wash the overflow tank, it is pretty simple, although you may consider getting a price on a new overflow tank as well. Usually if the head gasket is "really" blown, you'll know it, the coolant will really look bad, not just the inside of the pressure tank either, you'll have "beige" looking coolant, kinda like butterscotch pudding, "without all the calories!".
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Old 08-29-2001, 11:42 PM
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Join Date: Jun 1999
Location: Los Angeles, Calif, USA
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If the radiator is original, it is time to replace it with the updated version (with a metal tube insert inside the radiator neck) before the neck breaks.

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Old 08-30-2001, 10:41 PM
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Rebuilt or Restored?

Brother of The Benz,
You've been given enough informatiom to build a 300E.
I'm cxoncerned about your oil consumption. 1LTR per 2000 miles?
110,000 miles?
You have a very nice engine!
Excessive oil consumption according to MB Tech Data Book is 1 ltr per 650 miles.
If it were me, I wouldn't touch the engine.
My 103983 engine with 179,500 miles uses 1 qt per 15-1700 miles.
Her cylinder head has yet to be removed.
When finished you will be driving a $45,000 auto.
Accord to Automobile Magazine, the 300E is the best used car, bar now, on the market.
Happy Trails Beep Beep from the Spiderman in Houston!!!
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Old 08-31-2001, 08:17 AM
Posts: n/a

Glad to hear that the pushbutton control unit fixed your problem. It was no surprise.

To ensure that you don't blow the new unit, you need to check your auxiliary water pump current draw. It should be no more than 1.3 amps. If it is over this amount, flush, clean or replace to reduce the current draw. If you don't this will blow the new PB control unit.

Good luck,
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Old 09-26-2001, 06:01 PM
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Aux water pump per L.Bible

Brother of the Benz
As Larry suggested about the current draw of the aux water pump; my M/B tech suggested when that little rascal acts up, remove him and throw him into the darkest hole in Calcutta.
Happy Trails Beep Beep from The Spiderman in Houston!!!
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Old 09-26-2001, 08:20 PM
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Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 11,246
Welcome back Donald.
Are you saying just remove it from the system and leave the connector hanging? I don't think the one in my 300D works becaues when I turn the heat on high - it gets real hot in the car but I do not feel the heater water pump running.
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Old 09-26-2001, 09:10 PM
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where exactly is that aux. water pump located?
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