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Old 07-23-2002, 09:00 AM
Posts: n/a
High running temps solved!

First of all, I am new to the list and this is my first post. I felt that I should offer my recent experience with a hot running engine after spending a lot of time researching the tech forum with other members experiences. The car was diagnosed by the dealer as needing a new radiator and one auxiliary fan. Both were replaced and the problem was still there - running 100+ c .
After reading a post (sorry I can't remember exactly who) I decided to replace the thermastat. A local parts guy had a German made 82 degree thermastat made by "Go-Rad". The parts person indicated that this was considered an oem type replacement. I understand Behr is original equipment, but I wanted to take advantage of a lower temp rating. He indicated that even though the thermastat in the car may seem good by checking the hose to the radiator to see if it is hot , sometimes the thermestat doesn't open fully and can be restrictive as they get older. Anyway, popped the newone in and immediately back to 82-85 degrees. To anyone else with a hot running engine, I would suggest starting here first.

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Old 07-23-2002, 10:44 AM
J.HIDALGO's Avatar
Registered User
Join Date: Jul 1999
Location: Jax, FL
Posts: 1,785
KISS method!

Keep It Simple Stupid! Sometimes we go for the more complicated stuff...
'86 300E
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Old 07-23-2002, 12:31 PM
Registered Diesel Burner
Join Date: Aug 2001
Location: Northern Virginia
Posts: 2,911
The impression I've gotten from reading posts over the past year is that there has been a bad production run of OEM thermostats.

Don't know exactly what to do about it - but probably would look for an aftermarket part here.

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Old 07-25-2002, 02:44 AM
Registered User
Join Date: Dec 2000
Location: Fairfax County, Virginia
Posts: 856
Way to Go!

I have been thinking about overheating (since mine did) for awhile and it comes down to some simple stuff that gets all mixed up ... the logic trail is pretty clear.

Try this on:

If the engine overheats while running at 50 mph in normal temps with air conditioning off, it probably isn't:
- viscous fan
- electric fan
- maybe not even a pressure leak

It may be:
- tstat
- radiator
- maybe a pressure leak

I have yet to read of someone with a bad waterpump that affected cooling - they may blow a seal or bearing, but I am not sure how they would pump less unless vanes were worn down (hard to imagine) or the housing or inlet/outlet were clogged.

If overheats at idle, it could be:
- viscous fan
- electric fan
- pressure leak
- tstat
- radiator

OK, so what is easiest thing to do?
- replace tstat
- check for pressure leak at cap (most likely)
- see if electric fan is running (pretty easy)
- check to see if viscous or mag fan clutch is locking up (easy)
- last thing - replace radiator (it is the most expensive)

I am finally beginning to think right about this overheating thing ... although, I could be wrong.
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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Old 07-25-2002, 03:24 AM
David C Klasse's Avatar
CheFrac is Back!
Join Date: Jan 2001
Location: Mission Hills in the City of San Diego
Posts: 2,352
What were your symptoms? Was the engine running really hot in traffic?
Is the temp now @ 85 ALL the time (even in traffic??) ??

2006 E350 w/ 155k miles (Daily Driver)

1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)
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Old 07-25-2002, 07:10 AM
renok7's Avatar
Registered User
Join Date: Nov 2001
Location: Montréal
Posts: 95
I can't believe that the dealer went ahead and replaced the rad & fan without first trying a new thermostat. Makes one wonder.

'93 300E 4Matic
'98 Nissan Altima
'00 Yamaha Road Star Silverado
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Old 07-25-2002, 10:42 AM
Registered User
Join Date: Nov 2000
Location: St. Petersburg, FL
Posts: 200
Agree to start with thermostat first. I had the water pump blow on me on my last vacation trip, in South Carolina while I was heading back to Maryland. I kept water in the car, but it never even came close to overheating. That was my original worry and I finally got to the point where I just stopped to put water in it, but the temp was fine the whole trip. I used a lot of water, though!

But when I got the car from my Father-in-Law, he indicated that the car had been running a bit warm for some time. I thought, sheesh, I'm just going to put a new thermostat in without doing any testing just because I don't know how long it's been in there. It has run cool ever since.
1987 300SDL 265,000 mi.
1982 300SD 325,000 mi. (and holding)
1956 Packard Clipper 150,000 mi.
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