running hot in stop & go traffic - PeachParts Mercedes-Benz Forum

mjt2000 · #1 06-30-2003, 12:06 PM

Okay, I've read a thousand responses about the diesel engines running hot, but I'm still confused. I have an '86 300SDL that reaches close to the 120c (red mark) in hot weather with the a/c on, in stop & go traffic. It will lower when I start moving again. The Mercedes dealer says it should not reach that high and I need a new radiator. Another expert says i don't need a new radiator. The aux. fan is working.

HOWEVER, the owners manual says "During severe operating conditions and stop-and-go city traffic, the coolant temp may rise close to the red marking".

What is the real truth?

slowmoe · #2 06-30-2003, 12:18 PM

mjt2000,

Welcome to the forum!!

We didn't get all the post...

This is too high for my skin. First make sure your aux fans are working. If they are no comming on at 100C - this is the problem. Anyway, it would be on my 124. I do not know if the SDLs are set to funtion the same way... Anyone???

If they are fine and you know that your fan and fan clutch are okay, I would start with replacing the expansion tank cap(least expensive), then the t-stat and if the problem presists - the radiator (most expensive). If you do the raditor, I would do all hoses and the t-stat at the some time if it has been a while.

TX76513 · #3 06-30-2003, 12:44 PM

MJT - That is definately to hot. My 86 SDL never get's anywhere near the red mark. I think it may get a little warmer in TX than your home state. "Ever tried to go through Austin at about 5 PM?

Has your cooling system had a good flush? Thermostat been replaced lately? Have your degreased and presure washed the radiator fins?

sixto · #4 06-30-2003, 01:04 PM

When you get beyond 110C, do you hear the clutch fan and electric fan engage? The electric fan should be in high gear but it might be hard to distinguish from the low speed when the AC compressor is engaged.

If the clutch fan isn't engaging, do an archive search on variations and combinations of 'Toyota silicone fan clutch fluid'.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

mjt2000 · #5 06-30-2003, 05:00 PM

The thermostat has been replaced. Why does the manual state the the temp could hit the red mark when driving in stop-n-go situations?

sixto · #6 06-30-2003, 05:02 PM

MB wants to sell $2000 bare cylinder heads

Make sure your fans are working as they should before anything else.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

SSharma · #7 07-02-2003, 06:04 PM

This happened to me in my 300TD, turned out to be the water pump.

psfred · #8 07-02-2003, 06:51 PM

You won't get engine damage til you get up to the red zone, and I can see getting pretty hot stalled in, say Houston, with a slight following breeze at 4 pm in traffic.

However, you are running too hot. Do the quicky test for visco clutch operation (shut off when it is that hot while watching fan, it must stop within one revolution), and replace the thermostat (big PITA, it's on the side, in the lower radiator hose connection, you have to do it by feel). If the temp stays up, it's not the thermostat

If the visco fan and thermostat are OK, and the radiator cap holds pressure (check it, it's cheap) replace the radiator, it's MUCH cheaper than a new head. Flushing won't work if someone has been using green coolant in the past, the rad is full of insoluble crud, and you CANNOT remove the tanks and reinstall them leak free, no matte what anyone says. You are probably stuck with a plastic and aluminum replacement -- not enough demand for brass and copper ones (sadly, they last forever).

I'm fairly certain the techs have checked the temp across the rad -- easy to do these days with infared thermometers, and found cold spots indicating plugging. Rad is about $300 plus installation

My 300D had a new rad when I got it, but it has green coolant in it, to be changed this summer.

Peter

mjt2000 · #9 07-02-2003, 07:54 PM

Where can you get a radiator for $300. The dealer said it would be about $1500!!!!

P.E.Haiges · #10 07-02-2003, 09:07 PM

MJT2000,

$1500 for a radiator, he's not a dealer he's a stealer. Even $300 is on the high side. If you had a copper/brass radiator, you could get a new core installed for $200 or less and it would be good as new.

After you are on this site for a while, You will learn to stay away from stealers for most repairs. Replacing a radiator is a simple DIY project.

Before you buy a new radiator, take you radiator out and to a radiator shop. Have it flow tested and cleaned if necessary.

If you replace the radiator, I suggest you get an all metal brass/copper radiator instead of the aluminum plastic one like you now have. Do a search for where they are available.

P E H

PaulH · #11 07-02-2003, 09:26 PM

I had high temps with my '87 300SDL last summer. I had a bad fan clutch. Check it the way psfred suggested. Also, the aux fan comes on at 105. If you're cool on the open road, it probably isn't the water pump. Anyway , several people have given you some good information. Good luck.

#12 07-02-2003, 11:08 PM

I got a BRAND NEW rad here in FL that has brass conections to the tranny cooler VS the aluminum ones on the factory unit that managed to last 20 years and I only replaced because of a small crack in the plastic top part. Cost was well under $200.00 would have to check the invoice but this was just last fall I did the replacement so I'm sure of the price. VERY easy to replace. Don't see how a 86 model could be much more than what I paid.

#13 07-03-2003, 12:51 AM

I also removed the bimetalic bar that allows the clutch to engage on the visco fan. It took about ten minutes to do and now my fan is on all the time. I may replace the switch for the winter but I have not lost any gas milage to speak of so whay the heck I might leave it off.

Overall these cars are not that hard to work on and can be alot of fun.

good luck

bob