Could it be the damn thermostat??

[Agron80]

I had my radiator replaced 2 months ago, and now since the weather has been getting warm and humid, my car tends to overheat at idle. The temperature will shoot up to 105, 110 while i'm idling in hot weather, heavy traffic, etc, and then the aux fan kicks in until the temp drops. Also, If i shut the car off when its hot and restart immediately, the temperature starts off at about 110 and the aux fan kicks in right away. Could this be the thermostat?? or something bigger? Im planning on changing it this weekend. Thanks


Agron
1989 300E (108k miles)

I would check the viscouse fan clutch. It should be locking on at those temperatures at idle. Especially if it cools when you travel around 30 mph or faster.

[Benzmac]

Yes, if the thermostat was not replaced with the radiator, replace it first. Be sure the auxillary fans are working on BOTH speeds.

When the A/C is on, you need low speed aux fans.

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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

[jeffsr]

Normal to have an overshoot after shutdown when hot. Follow Benzmac's advice, do change the thermostat. You may have to bleed trapped air out of the cooling system as well. You didn't say that was done when the radiator was changed.

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Jeff Lawrence
1987 300e
1989 300e
1987 BMW 325

[ncarter]

First, as Jeff mentioned, make sure your coolant level is correct and make sure there are no air bubbles trapped in there. I think if you search this forum you'll find instructions on purging air from the system.

Second, if you're certain your coolant level is right and you have no air bubbles trapped, go ahead and replace the thermostat. Failure of the thermostat is a relatively common occurrence; replacing the thermostat is a pretty cheap and easy do-it-yourself job.

- Nathan
'83 240D, 252k miles

[Ken C]

When you replace the thermostat, don't overlook an important but tiny detail -- important if your thermostat's bottom housing lies at an angle (i.e., is not horizontal).
On the MB thermostats, there is a little "ball" valve (or, on some models just a hole) -- so when you install the thermostat, it should be rotated and positioned so that this valve is at the highest point. The purpose is to help to quickly purge air out of the system.

[ctaylor738]

Put the 75 rather than the 80 degree thermostat in if you replace it.

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Chuck Taylor
Falls Church VA
'86 300E 5 speed
'95 C220 (wife's car)
'98 Porsche Boxster
Past: '79 280E, '82 300D (18 yrs), '77 240D,
4 250C's

[Agron80]

Thanks alot guys, Im gonna follow all of your advice, and hope i'll cool down soon..

Regards,

Agron
1989 300E (108k miles)

[jeffsr]

Stay with the recommended t-stat 88 degrees C. It is not a good idea to go low b/c if you have other problems with the cooling system, you may mask them. Also, the M103 motor likes to run on the warm side. If everything is OK, stay with OEM numbers. If not, find out what's wrong and get it repaired.

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Jeff Lawrence
1987 300e
1989 300e
1987 BMW 325

[This message has been edited by jeffsr (edited 06-27-2000).]