129 500 SL engine operating temp. - PeachParts Mercedes-Benz Forum

MDE3 · #1 08-02-2008, 06:28 PM

My 1991 500 SL seems to run at about 100 - 105C most of the time regardless of ambient. I have never been in a stop and go traffic situation with it yet..so that makes me a bit nervous. Coolant appears normal in both level and appearance.

I did the search on here and found lots of posts about the 107 series cars, but not really anything definitive on the 129 when it comes to engine operating temps. The car has a hair under 80,000 miles at this point so I would be surprised if it has too much radiator build up/corrosion (it has been a garage queen for a couple of years with two previous owners)....but one never knows...I have only owned the car since May and put less than 400 miles on it at this point.

What are the normal suspects here..or is this to be expected?, Are there thermostat issues? Rad issues?

Thanks

plink49 · #2 08-04-2008, 09:27 PM

I would be extremely concerned about that high of a temp being "usual". Someone will surely correct me if I'm wrong, but I have quite a few years of experience with various models of MB, including the SL, and the "normal" operating temp of all of them is 80-85C, and that is running at highway speeds or sitting in traffic in 100F degree temps. I'm cetainly not a tech, but I would look at the thermostat first and then maybe the water pump. It's also possible that the gauge calibration is off. Whatever the cause it needs to be found because that is way to high of a normal running temp.

tecqboy · #3 08-05-2008, 09:52 AM

Check the thermal clutch on the main fan. Check when engine is hot, ( not running of course ); it should be engaged. I believe that at 105C the aux electric fans would also come on. Best thing to do is get one of those laser piro "point n' shoot" thermometers and check the actual temp of the engine at various points, especially around the temperature sensor which is connected to the VDO gauge.

http://www.maxtool.com/index/Digital_Infrared_Non-Contact_Thermometers.asp

ctaylor738 · #4 08-05-2008, 12:17 PM

I don't use the AC much, and my '96 generally runs a little over 80, and gets up to 100 in traffic.

On Saturday, though, the temperature was in the 90's and we had the AC on doing highway driving. I was suprised to see the temp sitting at 100.

If you are seeing 100-105 on the road with the AC off, then you should check out the radiator.

BRIAN123 · #5 08-05-2008, 05:15 PM

My 1990 500 SL had a high temp on the cluster, never overheated or lost fluid. I read that the resistors or some connection can go faulty. Once I replaced the whole cluster ( had some spedo problems also) the temp read normal.

I do notice the engine temp as a whole is VERY hot to the touch and heats up my entire garage when I park. Takes a while to cool down.

aam · #6 08-05-2008, 10:34 PM

Quote:

Originally Posted by MDE3

My 1991 500 SL seems to run at about 100 - 105C most of the time regardless of ambient. I have never been in a stop and go traffic situation with it yet..so that makes me a bit nervous. Coolant appears normal in both level and appearance.

I did the search on here and found lots of posts about the 107 series cars, but not really anything definitive on the 129 when it comes to engine operating temps. The car has a hair under 80,000 miles at this point so I would be surprised if it has too much radiator build up/corrosion (it has been a garage queen for a couple of years with two previous owners)....but one never knows...I have only owned the car since May and put less than 400 miles on it at this point.

What are the normal suspects here..or is this to be expected?, Are there thermostat issues? Rad issues?

Thanks

More info needed on what conditions.
But anyways.
I do have an 129.
I am getting a temp. 78 to 85

If you are on the freeway no a/c 100 is to high.

First start with a new thermostat 80 degrees.

To ck fan clutch, engine hot and running 2000 - 4000rpm clutch should be on
and fan roaring.

To ck Radiator, inlet / outlet should have at list 20 degree drop.

Regards.
aam.

MDE3 · #7 08-08-2008, 12:48 AM

All fans are working fine....when I first got the car a couple of months ago...I never noticed it going over 80C (but I also did not drive it much..purchased it for a friend who said he wanted it and it remained parked in the garage for most of the last 2 months..up until the past three weeks)....I just recently noticed it jumping up to the 100 - 105 C mark...same temp with or without ac, and as said the fans are all coming on with the ac on even at idle. Not losing fluids,...I did not put more than 400 miles on the car since acquiring, so the change happened sort of quickly...

JimF · #8 08-08-2008, 10:13 AM

Have you read the 6 items in MENU#17? Work your way through that list and see what happens. The first three (3) items are 'cheap'; the last two (2) are expensive.

If the radiator is original and it's not been flushed regurlarly or tap water was used instead of distilled water, the passages become partially plugged. So do a flush and see what happens. Can't hurt!