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Old 07-03-2002, 02:31 PM
Registered User
Join Date: Jun 2002
Location: Monrovia, CA
Posts: 490
300E Running Hot?


I recently bought my first Mercedes, an '86 300E with 93,000 miles on it. I'm trying to get it ready to take the family on vacation in August from L.A. to Washington/Canada. Driving in So. Calif., the AC is on quite often and it seems to run a bit hot. I'm assuming the line on the temp gauge between 80 and 120 is 100 C, and when I'm stuck in traffic or driving at low speeds through town the needle sometimes gets up almost halfway between 100 and 120. Is this too hot? With the AC off, the temp stays usually around 80 - 85. With the AC on, the electric fan comes on at some point, but doesn't seem to be pushing a lot of air. Will these fans slow down with age or use? Any easy way to test if it's running up to speed? Also, what's the best way to test the viscous fan clutch to make sure it's working as efficiently as possible.

I plan on replacing the original radiator before the neck snaps off, and the PO said the thermostat was replaced about 2 mos. ago, but I'll probably check it while I'm in there. What's the proper temp for hot weather use?

The water pump looks like it was maybe replaced, as there is silicone seal squeezed out of the joint, so I'm assuming it's probably good (no obvious leaks).

Where is the thermo switch that kicks on the fan? Can I test it with an ohmeter in hot water? What temp should trigger it?

Thanks for any help

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Old 07-03-2002, 04:43 PM
Join Date: Jan 2000
Location: Out on the old Santa Fe Trail
Posts: 232
Thumbs up "Hot" 300E

FWIW: My '86 300E w/152,000 on the "clock" exhibits the same behavior. My trusted mechanic says that this engine is noted for running on the hot side and not to worry about it as long as it doesn't get up into the red zone. Still, at 100f ambient, in slow traffic, it gives one pause. I stopped worrying about it.
62 220sb
67 250S
72 280SE 4.5
74 280C
77 300D
82 240D
85 190E 2.3
86 300E RIP 12/28/09
85 300SD
92 300D 2.5
00 E320 Current
Over 1,000,000 miles in Benzes, Since66

....and a whole passel of BMW 2002 and Tii
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Old 07-03-2002, 05:23 PM
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Join Date: Jun 2002
Location: maryland
Posts: 4
Cool hot 300e

I have a 92 300E and 93 400E that both seem to run a little on the warm side, especially at idle. They both have radiators that are less than a year old. Neck snapped off on the 300e and the fan clutch went on the 400e and threw the fan into the radiator (you should have heard how that sounded!!)

I haven't had any overheating problems yet but I do keep a concerned eye on them. The 300E did fine at idle in the heat today and it is 100+ here. The thermostat reading usually never goes above 100 on the console. I guess it is up to you but just keep an eye on it.
1991 190E (decommissioned)
1992 300E
1993 400E
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Old 07-03-2002, 06:54 PM
Posts: n/a
I really tested my cooling system over the last couple of days when the temperature went up to 36-38degC (over 100degF)
I got stuck in trafic for close to 1 1/2 hour, bumper to bumper.
After a while, the A/C, pushing nice cold air settles down from high speed fan to a nice breeze.
My temp. gauge never touched the halfway mark between 80 and 120.
I had my radiator, thermostat, cap, hoses replaced last spring after a good flush/cleaning of the cooling system.
Contrary to what some believe, these cars are not designed to run hot (at least, from my experience)
With everything in order, these cars can support extreme heat without suffering.
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Old 07-04-2002, 01:07 AM
Registered User
Join Date: Jul 2001
Location: Mexico
Posts: 550
I notice the same thing..when the car is at idle or slow..the engine temp raises..but when u start moving drops.cause of the cold air getting into the engine..

solution.....dont drive in traffic...take the bus..subway.....

reduce the earth!
87' 300E champagne - Euro headlights and corners, 8-hole rims, 140,000miles/220,00km.
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Old 07-04-2002, 01:08 AM
Registered User
Join Date: Jul 2001
Location: Mexico
Posts: 550
why is it so hot in toronto...
its like 35.celcius...

I cant take it anymore..
i want to move north in the summer.......LOL!!!!!
87' 300E champagne - Euro headlights and corners, 8-hole rims, 140,000miles/220,00km.
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Old 07-04-2002, 08:53 AM
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Join Date: Feb 2002
Location: Bulgaria, Sofia
Posts: 584
My 190e 2.5-16v does exactly the same thing. To be honest I feel a little uneasy when I see the temp gauge going to 100 when I'm stack in traffic.
190E 3.0-24v (M104 980) turbo @ 0.8 bar
1/4 mile: 2.483 / 13.540 / 175.17 km/h (street tires)
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Old 07-04-2002, 11:01 AM
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Join Date: Mar 2002
Location: Las Vegas
Posts: 9
I have an '84 500SEL Euro with 191,000 miles on it. I love the car but an overheating problem has plagued it for years......only, however, in stop-and-go traffic on a hot day. Driving in Atlanta in the summer is an adventure. I've only been in the red once (and luckily reacted quickly enough), but the temp always gets to 110 during the summer months. 110, by the way, is what the factory manual states as a perfectly normal operating temperature in hot weather. The problem is that if I am stuck in traffic for very long the auxillary fan will eventually lack capacity to hold that temp and it will head to 120 (red). To date every possible component has been replaced, every check has been made, and every additive has been no avail (please take my word for it). Experts have repeatedly tried and failed to find a "solution". All I can do is rationalize that I would have put all that repair money into the market and lost it anyway. I have always referred those very experts to the factory service manual which contains a statement suggesting the car be shifted into neutral in stop-and-go traffic on hot days in order to preven the transmission from causing a build-up of heat. It is obvious to me that even mercedes recognized that cooling may be marginal in these models under certain conditions, or why would they even suggest such a thing.

I've heard that replacing the engine fan with an after-market electric fan, which obviously produces more air across the radiator at idle, can fix the problem. I've also heard that a custom, more efficient radiator can be made. I would greatly appreciate any help, if anyone has any ideas. Maybe someone out there can find a solution for all of us.

Thanks so much.
Don's 500SEL Euro
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Old 07-04-2002, 01:09 PM
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Moderating, Eh?
Join Date: Feb 2000
Location: Canada
Posts: 1,774
Mine sometimes hits 100 when idling in traffic on hot summer days like we've been having the past week up north here. 34 C and 45 C with the humidex! I thought Canada was supposed to be cold? :

I miss January...
2007 E550 4Matic - 61,000 Km - Iridium Silver, black leather, Sport package, Premium 2 package
2007 GL450 4Matic - 62,000 Km - Obsidian Black Metallic, black leather, all options
1998 E430 - sold
1989 300E - 333,000 Km - sold
1977 280E - sold
1971 250 - retired

"And a frign hat. They gave me a hat at the annual benefits meeting. I said. how does this benefit me. I dont have anything from the company.. So they gave me a hat." - TheDon
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Old 07-04-2002, 01:32 PM
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,508
This might be one of the bast threads about heating and cooling and temperatures.

Take notice of the posting by tkamiya where he lists the temperatures that the thermostats start to open at (85-89) and is only fully open at 102 degrees.

Also interesting is the electronic fan cuts in at 107, and turns off at 100 degrees.

He also lists the maximum allowable temperature at 130 degrees.

LOGIC REQUIRED -Engine Temp What Is Normal??????
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".
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