not-front-rule

Overheating

Welcome to the Mercedes-Benz Club of America Forums
Here, you'll find members en masse who can talk, guide, answer or listen to your Mercedes-Benz related questions and comments. Participation in the forums is free to Club members. If you're a guest of this site, you'll have access to our read-only discussions. Like what you see? Join the Club to get full Q&A privileges. If this is your first visit, be sure to check out our FAQ page.  To start viewing messages, select the forum that you want to visit from the selection below.

Forum Jump

9 replies [Last post]
Former Member
jblanc's picture
San Jose, CA
Offline
Joined: May 27th, 2008

Posts:
28

Vehicles
1991 300SE
1990 300SE

my 1990 300 SE is overheating when i stop in a stop light. It is very hot in san jose this week reaching 90 or so. When i drive, the temperature stays at around 80 but 5 minutes into the highway starting moving to 85 or even 90 and exiting freeway idling at a stop light reached almost 100. We checked the coolant and it was full so i wonder what else it could be. In the cool days it runs well.

Share this
__________________

jmb

Guest
raymo's picture
Offline

Posts:
48
Re: Overheating

There are a number of threads about overheating, but the first thing I'd check is thermostat not opening all the way. After that check for a partially blocked radiator.

Member
Cal Learner's picture
Marysville, CA
Offline
Joined: October 27th, 2008

Posts:
273

Vehicles
1988 260E
Re: Overheating

Welcome. Many threads on overheating generally, and of M103 motors like yours in the archives to search on. Are your auxiliary fans, the two at the front of the engine just behind the grille, coming on when it gets hot or when you run your A/C? They're supposed to create airflow over the A/C condenser and radiator when the car is stopped, so that the engine doesn't overheat. When you're moving, the flow of air takes care of that, but when you come to a prolonged stop, like at a traffic signal or drive-thru, there's no other airflow to keep the radiator cool without these auxiliary fans. Check that, along with the suggestion already made to see if there is debris (leaves, etc) between the condenser and the radiator, which would block good airflow through the condenser and rad. If you can't tell whether the aux fans come on or not, there are a couple of very simple tests to check whether they're still good or not. Try this thread:

http://mbca.cartama.net/showthread.php?t=30124

Post results and let us know how it goes.

__________________

Member
George Murphy's picture
Oak Ridge, TN
Offline
Joined: October 10th, 1978

Posts:
1695

Vehicles
1999 C43 AMG
Re: Overheating

Check your fan clutch - it may not be engaging at higher temps in traffic, but highway speed air flow cools radiator adequately . .

__________________

Regards,

George Murphy

MBCA Technical Director

865-482-9175

1999 C43 AMG

Former Member
jblanc's picture
San Jose, CA
Offline
Joined: May 27th, 2008

Posts:
28

Vehicles
1991 300SE
1990 300SE
Re: Overheating

the mechanic tells me that the 2 fans have nothing to do with the car temperature as mesasured by the indicator inside. He said those two fans only operate when i have the AC on and since it seems that there is not much freon the fan dont operate. So he said to fill up the freon first. Also he tells me not to worry if the temp goes up to 100 because until it goes closer to the 120 degrees which is where the red mark is, then the car is ok. In the winter i saw it runs at 80 or 82 so i worried when i saw it going to 100. Does ths make sense?

__________________

jmb

Member
Cal Learner's picture
Marysville, CA
Offline
Joined: October 27th, 2008

Posts:
273

Vehicles
1988 260E
Re: Overheating

jblanc;166592 wrote:
the mechanic tells me that the 2 fans have nothing to do with the car temperature as mesasured by the indicator inside. He said those two fans only operate when i have the AC on and since it seems that there is not much freon the fan dont operate. So he said to fill up the freon first. Also he tells me not to worry if the temp goes up to 100 because until it goes closer to the 120 degrees which is where the red mark is, then the car is ok. In the winter i saw it runs at 80 or 82 so i worried when i saw it going to 100. Does ths make sense?

The issues are getting confused here, and either your mechanic is giving you bad info or you're misunderstanding what he's telling you. You asked why your engine might be overheating, and you were given some possible causes, including bad airflow b/c of blocked condenser/radiator and inop aux and magnetic fans. Now, you're talking about temp gauge in the instrument cluster having nothing to do with the aux fans. Read the thread I gave you in post #3. Aux fans are controlled by a 2-wire temp sensor with blue base (identified in the MBz service CD as sensor B10/8). The temp gauge in the instrument cluster receives its signal from a 1-wire sensor (B13). These two sensors have nothing to do with one another, and B13 has nothing to do with your engine overheating or the operation of your aux fans. It is not true that the aux fans operate only if the A/C is engaged; they're supposed to operate on high speed whenever the engine is under a high thermal load (beginning at ~105C), regardless of what the A/C is doing at that moment. The A/C could be disengaged, and the high fan should still come on. As far as low refrigerant levels affecting the fans, that's also not true. Low refrig level will keep the A/C compressor from coming on, but it won't prevent the aux fans (or, for that matter, the magnetic fan) from running whenever the temp sensor (B10/8) measures engine temps of at least 105C.

Your engine temp will always rise slightly with high ambient temps and slow, city driving, particularly while operating the A/C. That's why it's so important that both the magnetic fan and the aux fans work correctly, b/c their job is to provide airflow over the radiator to compensate for the fact that the car is not moving fast enough to create its own air flow. Does that make sense? On a very hot day, it could reach 100C with prolonged stops for traffic signals or drive-thrus, etc. Mine normally doesn't reach 100C, even with the South Florida heat, but I suppose it might in summertime Phoenix. The obvious, easy, inexpensive things to do about overheating are: (1) ensure that the radiator and condenser are not blocked, (2) ensure that the magnetic fan clutch engages at higher temps, (3) ensure that you have a good thermostat, (4) ensure that you're using the proper coolant mixed 50:50, and (5) ensure that your aux fans come on when they're supposed to.

P5185577x.jpg
__________________

Member
signifer's picture
Ashburn, VA
Offline
Joined: August 30th, 1994

Posts:
148

Vehicles
1987 190E
1990 300E
2006 E350
Re: Overheating

Maybe I'm missing something, but as far as I know the temp gauge getting to 100 when sitting in traffic with an outside temp in the 90s is perfectly normal; you only need to worry if it gets into the red zone. Does it have any other signs of overhearing? (I would still check all the things mentioned to be sure everything is working but I'm not sure you have a problem.)

Best regards,
Richard

__________________

Former Member
jblanc's picture
San Jose, CA
Offline
Joined: May 27th, 2008

Posts:
28

Vehicles
1991 300SE
1990 300SE
Re: Overheating

Tks so much Cal Learner. Just to summarize, the magnetic fan is the big one in front of the radiator and has nothing to do with engine overheating so i wonder what it is for. It tells you how it works by checking the gage in the instrument cluster (B13). I thought the instrument cluster was actually what measured the temperature of the engine

THe 2 aux fans are smaller and in the front. THese are controled by the B10/8 wire tem sensors and those are the ones which turn of if the car overheats or when you have the AC on.

__________________

jmb

Member
Ferdman's picture
Chester Springs, PA
Offline
Joined: October 15th, 1998

Posts:
1883

Vehicles
1998 E320 Sedan
1995 E320 Sedan
1991 300CE
Re: Overheating

Jose, some fluctuation of the needle on the temperature gauge is normal. The various fans keep the engine from overheating and activate at different set points. What's important is that the engine doesn't overheat. From your description it would appear that your engine's cooling system and auxiliary fans are operating normally.

__________________

Fred Hoelzle

Member
zalsaigh's picture
Grand Island, NY
Offline
Joined: November 20th, 1991

Posts:
37

Vehicles
2004 SLK320
2004 ML350
1991 300SE
1974 280SL
1972 250C
1967 230SL
Re: Overheating

I had a smilar problem with my 91 300 SE. I replaced the fan clucth and that solved the problem. Good Luck.

__________________

Al-Chemist
Niagara Section, NY
04 ML350
04 Crossfire/SLK
91 300SE
74 280 SL
72 250 C
67 230 SL

Forum Jump

Share this