Running warm on highway - PeachParts Mercedes-Benz Forum

chrisgt · #1 07-25-2016, 07:55 AM

Now that it's finally getting hot in Maine, my 84 300td has been running a bit warm.
I just took it for an 800 mile roadtrip through NY, average outside temp was probably 95F. On the highway engine time was probably 95C, going up long mountain passes in VT the temp would hit 100 and sometimes start to crest 100 a little bit, at which point I'd turn off the AC which would keep it from climbing. I have a 16" aux fan shoehorned in, sitting idle in traffic it doesn't go over 100 with the AC running.

Is this cause for concern? I was thinking maybe I should pull my radiator out, chemical clean and flush it. My water pump is brand new (replaced couple months ago because old one was leaking)

Rogviler · #2 07-25-2016, 10:35 AM

Have you checked for leaves and crud between the radiator and condenser, or crud plugging up the radiator fins? That's what it was on mine ('85 TD). Could be something more complex, but simple stuff first.

-Rog

chrisgt · #3 07-25-2016, 10:41 AM

Funny you mention that... I pulled the radiator out and.... yea this.

https://lh3.googleusercontent.com/-ES_JOn9ivc0/V5YlQc3E2lI/AAAAAAAAAhA/Km8nibEf0-My01TEFUA6uzXxtKEMvPyNgCCo/s2048/IMG_20160725_101207161.jpg

Pressure washed it from both sides a few times, doused it with brake cleaner, pressure washed again from both sides. Now it's shiny.
Right now it's sitting full of CLR for an hour, then I'll flush it out, give the whole thing a good wash, make sure I didn't get any water in the AT cooler lines (capped them, so hopefully not) and see how it goes.

oldsinner111 · #4 07-25-2016, 10:42 AM

original radiators do need replacement after years of scale.Get a lower T Stat too.

chrisgt · #5 07-25-2016, 10:57 AM

Lower thermostat? I only see one listed, I was just going to get the OEM mercedes one from pelican because it's only $28 and probably the best quality replacement.

Or do you mean lower temp. I'd rather get the stock 80 degree one, I do drive the car in cold weather and like my heat working.

t walgamuth · #6 07-25-2016, 01:32 PM

Yeah, Its probably better to fix the problem than install a lower temp stat.

dkveuro · #7 07-25-2016, 02:52 PM

Mercedes wrote about high coolant readings. They said that coolant rising to 100c is normal after a vehicle slows in traffic as long as it resumes 80c to 90c back on highway, or...does not puke coolant out of the system.

So...if your not loosing any coolant. this is within the limits Mercedes is comfortable with.

However...as has been said, you may need to invest in a new radiator.

The other thing you might check is to see if the engine is not getting more than 12 psi of boost. Higher boost will increase engine coolant temperatures although I have run a 123 at 20 plus psi but with a new radiator. Coolant did rise above 80c but never overheated....ie: Puked.

.

,

chrisgt · #8 07-25-2016, 03:40 PM

Well with the radiator flush and cleaning out the fins, the problem seems to be mitigated.
It will now sit idle with the AC on full just over 90 degrees, right around 90 with the AC off. Which also means I did a good job rebuilding the fan clutch a few weeks ago as the electric fan doesn't run when the AC is off. I still might have the radiator hot tanked because I know I didn't get all the crud out.
Also, probably wise to replace the thermostat as preventative maintenance.

Also, as an added benefit, the AC works better. I guess more airflow through the radiator and less heat build up helped that, too

Demothen · #9 07-25-2016, 04:22 PM

How did you rebuild the fan clutch?

yuke · #10 07-25-2016, 04:31 PM

On my 85 300sd with 617 motor I was always running about 100c. a little higher then what the normal 80c. I tried everything including letting vinegar sit in the radiator for 2 weeks probably too long because then it ate a hole in the trans. cooler compartment and I got coolant in my trans. not good so long story short after replaceing radiator I got it to run at normal 80c. They say you can run all day long at 100c. at no harm to engine I was for about a yr. till I replaced radiator.

chrisgt · #11 07-25-2016, 07:30 PM

I know I didn't get all the stuff out, but it did a pretty good job. The radiator itself is in really good shape so maybe this winter when it's off the road (don't want to rust it out) I'll have the rad tanked. New radiators are ungodly expensive, I'd rather not have to buy a new one.

Quote:

Originally Posted by Demothen

How did you rebuild the fan clutch?

I followed this fantastic post by jbaj007.
I used this viscus fluid off amazon.

vwnate1 · #12 07-25-2016, 08:00 PM

I had some cooling issues on my various MB's and used the citric acid cleaning to very good effect .

I didn't remove the radiator , I flushed the entire system with the heater on , this did the trick ~ there was scale every where in the system and the heater's matrix is designed to act as a sediment trap , it took long to clean that out than the rest of the system .

In the end I had to open the heater hoses and flush it back and forth , each time it'd puke out a little bit more rusty silty crud .

chrisgt · #13 07-25-2016, 09:15 PM

Since my heater core, aux water pump, and heat control valve all work properly, I didn't want to temp fate my flushing the entire system as a whole... Besides, the only way to clean all that disgusting crud off the fins was to remove the whole thing.

vwnate1 · #14 07-25-2016, 09:28 PM

Fair enough ~ it's true that the crud blocking the fins is often not visible before taking the radiator out .

Never the less , crud else where in the cooling system can still be a problem even with a new radiator .

Due diligence and time are are your friends here .

chrisgt · #15 07-25-2016, 10:03 PM

That is true, I'm just gonna run it as is for now, see how it does before moving deeper. I don't like to mess with more than one thing at once, otherwise when stuff goes wrong I don't know where I caused the problem.

I'm not worried about overheating and damaging anything, so I have some time to watch it and observe.